The "Plane on a Treadmill" Question
The riddle/question is on every other forum. I figure I should bring the torture here, as well.
A plane is standing on a runway that can move, like a giant treadmill. When the plane's engines throttle up, it begins to move forward, but the treadmill is made to match the forward speed of the plane, only in the opposite direction. So, as the plane moves forward, it moves backwards beneath the aircraft.
As the engines throttle up, does the plane take off?
I've never heard this before. But no, a plane takes off because its wings generate lift, which it can only do when moving forward.
Why would the plane not move forward?
no, unless the engine thrust > wt. of plane... but that's a lot of thrust for your average puddle jumper.
edit: the Harrier could 'jump' off a moving runway ;)
The engines of the plane push against the air, so the runway doesn't matter. The wheels will rotate as much as they have to as the plane pushes against the air. The runway is not relevant once the plane's engines start.
No. No lift, as UT said. Planes do not take off from a stationary position. What would you expect it to do, suddently leap in the air? At what speed? From zero to what, in how many seconds? Same question: if you drop a paper airplane on the ground, will it suddenly leap in to the air and fly for no apparent reason? Same answer: No. The end.
The plane will move forward but not enough to gain enough lift. The wheels on the ground fight the force of gravity, until the plane has enough forward momentum for the wings to produce lift. Now the wheels are not fighting the force of gravity as hard so the engines have to fight it harder. That's my story and I'm stickin to it, until someone posts something that makes it look bad.
The plane will move forward but not enough to gain enough lift. The wheels on the ground fight the force of gravity, until the plane has enough forward momentum for the wings to produce lift. Now the wheels are not fighting the force of gravity as hard so the engines have to fight it harder. That's my story and I'm stickin to it, until someone posts something that makes it look bad.
The friction of the wheels in this question and, even in the real world, is pretty much of no consequence. The engines, being as powerful as they are, should easily be able to overcome it.
Hearing people explain this question and their answer has made me drop this into my "interview pool", alongside the "explain why manhole covers are round" question. I love it. :)
Of course there is lift. The plane will move forward against the air, and twice as fast against the runway. It will take off just like it normally would. A plane's wheels are not powered. They spin freely as the engines push against the air. The air is stationary, only the runway is moving.
No! The engines (normally) move the plane forward to make air go across the wings and produce lift. No going forward, no lift, no take off.
If it were a car and depended on the friction between the tires and the ground to move forward, that would be another thing. But in this case, the backward thrust of the engine is what's moving the plane forward. I don't think the treadmill would have much of an effect on the outcome, if any.
Think of it this way. A plane already in the air flies just over the treadmill. Does the movement of the treadmill affect the movement of the plane?
It's not already in the air, and it will never get there from a staionary position. The engines DO NOT "push" the plane into the air.
It's not already in the air, and it will never get there from a staionary position. The engines DO NOT "push" the plane into the air.
Sure they do. What, you think the wheels do it?
No. The movement of air over the wings does it. No movement = no lift = it will not take off.
It's not already in the air, and it will never get there from a staionary position. The engines DO NOT "push" the plane into the air.
The engines push the plane through the air until lift is achieved. When a plane taxis on a runway, it uses its engines pushing against the air to make it move. The wheels just follow the plane along.
The plane will move forward but not enough to gain enough lift.
Of course there is lift. The plane will move forward against the air, and twice as fast against the runway.
No, read the question:
When the plane's engines throttle up, it begins to move forward, but the treadmill is made to match the forward speed of the plane, only in the opposite direction. So, as the plane moves forward, it moves backwards beneath the aircraft.
The plane cannot move against the air, at all.
The wheels just follow the plane along.
Forget the wheels. The plane needs to move against the air to generate lift, to take off. It can't move against the air, so it can't take off.
OK, OK I'm convinced.
Which makes me a worse job candidate, except that I have the ideal answer to all such interview questions:
Oh, I've already heard that one.
That is, unless you want to use a constructed answer. The answer to why manholes are round? Because men are round. Duh.
"What would you do for a Klondike bar?"
I'm sorry, but I can't discuss salary during a first interview.
Sure, all it would need is a wind blowing at the front of the plane, that is strong enough to create lift.
Sure, all it would need is a wind blowing at the front of the plane, that is strong enough to create lift.
The plane pushes against the air, right?
Picture a different scene. You are in a canoe in a raging river, but you have a pole, and you are using it to push your way up the river. The water is going past the canoe at a very high speed, but since you aren't pushing against the water, this doesn't matter. You push against the ground with a pole.
Here, the plane isn't pushing against the runway, it's pushing against the air. The runway doesn't matter.
It would not take off.
the treadmill is made to match the forward speed of the plane
not the speed that the tries rotate. The plane will not move forward, cannot take off.
Picture a different scene.
No, picture the scene we're talking about: a plane hopping right into the air, straight off the ground. (Commercial jetliners are not designed to do this!) And then say to yourself "oh, gee, what an incredible dumbass I was for even entertaining the fact that this might be possible" . . .
Here, the plane isn't pushing against the runway, it's pushing against the air. The runway doesn't matter.
And the "pushing" doesn't matter, either. Only the forward motion does. There is no forward motion
according to the question.
You're messing with me now, aren't you? You know it takes off, but you are playing devil's advocate just to keep the argument going.
IM ON UR RUNWAY SPINNIN UR TIREZ
There is no forward motion according to the question.
The question doesn't say that.;)
:D
ok... the pilot 'spins' up the runway to about 150 mph, quickly turns around 180 deg. and 'rides' the runway with enough speed for lift!
The question doesn't say that.
Yes it does:
A plane is standing on a runway that can move, like a giant treadmill. When the plane's engines throttle up, it begins to move forward, but the treadmill is made to match the forward speed of the plane, only in the opposite direction. So, as the plane moves forward, it moves backwards beneath the aircraft.
It matches the forward speed,
cancelling all forward motion. UT's animation repeatedly says "as the plane moves forward" but that is not the scope of what we are discussing.
We are discussing a stationary plane.
Fuck the wheels, fuck the treadmill, fuck the thrust. Lift is produced by air
moving across the wings. [SIZE="4"]Moving.[/SIZE]
I found it after googling for the problem... turns out it was fought over by folks on a physics board, so I feel a little less foolish...
Flint. The wheels don't matter as far as forward motion is concerned. As the graphic that UT says, the wheels will just spin twice as fast. It doesn't matter how fast the treadmill is going backward, because the plane's pushing against the air, not the ground.
:corn:
(Not being sarcastic...I find this debate fascinating)
Flint. The wheels don't matter as far as forward motion is concerned. As the graphic that UT says, the wheels will just spin twice as fast. It doesn't matter how fast the treadmill is going backward, because the plane's pushing against the air, not the ground.
Fuck how fast the wheels are spinning. No forward motion = no lift.
The only item of discussion here is how you read the question. Stationary planes (commercial jetliners) do not jump into the air. Ever.
So, as the plane moves forward, it moves backwards beneath the aircraft.
If I understand you, the above part of the problem set means "no forward motion" to you. I don't think it does. It would for a car. It doesn't for a plane.
If I understand you, the above part of the problem set means "no forward motion" to you.
It doesn't mean that to me. I would say there is most certainly forward motion in the way I described it. The wheels are free spinning despite the treadmill.
If I understand you, the above part of the problem set means "no forward motion" to you.
No, this part does:
...the treadmill is made to match the forward speed of the plane, only in the opposite direction.
There aren't
two different reasons for the wheels to spin. They only ever spun because the plane was trying to move forward, and the treadmill matches the forward speed, cancelling it. If the plane thrusts harder, the treadmill continues to cancel it's motion. There is no tip-over point, here. The treadmill prevents the plane from moving. The plane cannot take off from a stationary position.
If the plane thrusts harder, the treadmill continues to cancel it's motion. There is no tip-over point, here.
Get a motorized treadmill and a bicycle. Hold the bicycle in place and turn the treadmill up as high as it will go. Are you having to fight very much to keep the bike stationary? No -- the friction between the bike frame and wheels is very low. Now, push the bike forward. Is it taking much effort? Not at all.
Now, push the bike forward. Is it taking much effort? Not at all.
...the treadmill is made to match the forward speed of the plane, only in the opposite direction.
It doesn't matter how "hard" it is. In
this scenario, you
can't do that.
The plane will move forward, no matter how fast the treadmill is going. The treadmill can't cancel the forward motion of the plane, because the plane's speed is not determined by the wheels. If you hold a hotwheel car in your hand, and put it on a treadmill, you can move it forward no matter how fast the treadmill is going. Likewise, the jet engine will move the plane forward no matter what the treadmill and wheels are doing.
Now, if it were in a wind tunnel, and air was blown to cancel the jet engines, that would be a different story.
You're right: if you ignore the question you can get whatever answer you want.
Nothing in the question says the plane is stationary. Just that the treadmill moves. But the treadmill can not stop the plane! The assumption that the plane is made stationary by the treadmill is something that you are bringing in, and is the trick part of this trick question.
The thrust of the engines pushes the plane and axles the wheels are spinning on forward (as stated in the problem). Once the plane begins to move, then the treadmill turns on. The treadmill accounts for and this forward motion, speeds up, and causes the wheels to spin around the axle. The friction holding the still plane in one place is gravity, a downward force. Once the treadmill is going, the thrusters create a vector of force in the forward direction enough to overcome the downward force of gravity. The plane continues to move forward faster and faster and the treadmill/wheels continue to spin also, but again, only around the axle. Eventually the plane will gain enough forward speed to create lift under it's wings as it would on a stationary runway.
My initial response was no take off, until I tried to explain why, then I had to change it to damn, I think it will take off.
...the treadmill is made to match the forward speed of the plane, only in the opposite direction.
It doesn't say "wheel motion" - it says forward speed. No forward speed. Forward speed cancelled. No motion. No lift.
I'm confused. If the treadmill does not negate the forward motion of the plane caused by the jet engines, the entire question seems moot and pointless in its quest to be clever. If it DOES, as it seems the question meant to intend, then I agree with Flint.
But I'm not a scientist and I don't even play one on TV.
If the treadmill does not negate the forward motion of the plane caused by the jet engines...
There aren't two different reasons for the wheels to spin.
Sorry I'm late to this discussion, but I'm with Flint. The problem, as stated, does not allow for the plane to develop any velocity relative to the air. Only this relative velocity (wing vs. air) can give you lift. (All aeronautics engineers: No Lift Without Drag!)
Doesn't matter what happens "in real life," this statement
the treadmill is made to match the forward speed of the plane
makes it moot.
Hey, that's what I said, Pie...and now I feel really intelligent because you ARE a scientist-type. :)
In fact, a plane that's stationary with respect to the runway can take off -- if there is a strong enough headwind. Don't believe me? Try holding on to a kite on a windy day.
Eventually the plane will gain enough forward speed...
No, it won't:
...the treadmill is made to match the forward speed of the plane, only in the opposite direction.
Again: not "wheel motion" but
forward speed. The specific scanario we are discussing involves a
stationary plane.
The plane will move forward, no matter how fast the treadmill is going. The treadmill can't cancel the forward motion of the plane...
Yes it can, because the question says it can, and does. That is what we are discussing:
...the treadmill is made to match the forward speed of the plane, only in the opposite direction.
Flint, the wheels are in contact with the runway. The wheels are spinning around the planes axle. The forward thrust of the plane moves the axle forward, while the wheels keep spinning around the now moving axle.
After thinking for a bit, it seems pretty clear to me that the plane will not move forward, and hence will not take off. I have written a cogent, well-argued, absolutely devastating post to explain to all you fucking idiots who think the plane will take off, that it will not.
As is my habit, I then reread the post and went about editing it to make it more organized, introduce additional supporting points, and just generally kick rhetorical ass. (Anybody who thinks my posts are incoherent should see my first drafts.)
In the process of doing so, I became convinced that the plane would indeed take off.
It's all about the wheels. What forces are at play here? We've got the engine pushing forward. We have the treadmill furiously spinning backward. Since this is physics word problem land, we don't have to worry about friction, and we're ignoring considerations of the plane changing speeds. It's true that the engines are pushing against the air, not the ground--but they're also pushing against the plane. The treadmill is also exerting a considerable force of identical magnitude in the opposite direction. However, this force has no purchase on the body of the plane. Because the wheels are spinning freely, none of the reverse force from the treadmill is applied to the plane.
I think we can all agree that we'd like to see it tried, preferably with a 747 or a Concorde.
Picture a bike on one of those moving things in the airport. If you stand off of the moving tread, and hold on to the bike while walking forward at the same speed the tread is moving backward, the bike will move forward. The wheels will now be spinning twice as fast, but the bike will be moving as fast in the opposite dirsction as the tread. In the plane example, the forward thrust of the engines = you holding onto the bike. The plane will move forward, ever faster.
Right steve!! because they are spinning around an axle.
The treadmill will have some backwards force, but not enough to prevent the plane from moving forward.
The treadmill is moving 140 mph backwards while the plane is moving 140 forwards. In order to prevent the plane from moving, the treadmill has to accelerate to the point where it produces more drag on the wheels and axles than the jet engines do. Not 140 MPH, more like 14000.
The stated scanario is that all forward motion is cancelled. As to "how" the treadmill does this, that's a different question.
You sound like you're itching to re-do the problem with accurate friction coefficients included!
The stated scenario is that the treadmill moves the same speed as the plane. According to your (flint's) take (faulty) on the question, the plane doesn't move and therefore the treadmill doesn't move.
Re-do whatever you want, but the answer to
this question is: a stationary plane will not take off spontaneously.
According to your (flint's) take (faulty) on the question, the plane doesn't move and therefore the treadmill doesn't move.
No, the stated (post #1) take (this thread) is that the plane and the treadmill move at equal speeds, in the opposite direction.
Another way to look at it: can a sea plane take off if it's floating down a current faster than its takeoff speed? Sure, the minute its props spin, it will be generating enough force to overcome the friction of the moving water.
Just look at it the way is is, as stated.
You've got velocity and acceleration. The engines are applying force to the plane and therefore accelerating it. The treadmill has velocity, but it cannot impart any acceleration to the plane.
blah blah blah
The plane cannot move forward because the question tells you that. It doesn't matter "how" . . . [SIZE="4"]READ THE QUESTION.[/SIZE]
The riddle/question is on every other forum. I figure I should bring the torture here, as well.
A plane is standing on a runway that can move, like a giant treadmill. When the plane's engines throttle up, it begins to move forward, but the treadmill is made to match the forward speed of the plane, only in the opposite direction. So, as the plane moves forward, [COLOR="Red"]it[/COLOR] moves backwards beneath the aircraft.
As the engines throttle up, does the plane take off?
My bolding.
No labrat posts without going back to the butt! :)
Flint, I totally agree with you. The question says the motion is cancelled. No motion...doesn't matter how.
Ya, we know about your butt, okay. It's so awesome, etc.
If you read the red [COLOR="Red"]it[/COLOR] in my quote as referring to the plane, then the answer would seem to be no, the plane can't take off. I read it as referring to the treadmill, thus the plane will take off.
The problem doesn't. It says the speed of the treadmill equals the speed of the airplane. It doesn't say the airplane is prevented from moving forward.
It says the speed of the treadmill equals the speed of the airplane. It doesn't say the airplane is prevented from moving forward.
If the plane moves at a given speed in one direction, and the treadmill moves at that same speed in the opposite direction, what is the net speed of the plane? The debate is not: "how does the treadmill know what speed the plane is going?" it simply says the speed is matched, thus cancelled.
You're assuming that, in rotating, the treadmill exerts a backward force on the body of the plane. It's only interacting with the wheels.
Flint, when the treadmill moves, what part of the plane is it moving?
The wheels.
The wheels are free-spinning around their axles.
So, as the plane moves forward (which i thought you said it couldn't do ;)) the wheels end up spinning faster and faster as the treadmill matches the forward motion of the plane.
If the plane is moving forward at X mph, and the treadmill is moving backwards at X mph, then the net forward speed of the plane is X mph, but the wheels are spinning at 2X mph. The treadmill is matching the speed of the plane, not the speed that the wheels are turning.
another way to look at this is to consider the aircraft carrier: the planes are 'launched' with a catapult. But the wheels are on the deck, and the catapult moves much faster than the deck. The deck could be moving backwards and still the catapult could launch the plane.
Did my bike example make sense to you?
A plane is standing on a runway that can move, like a giant treadmill. When the plane's engines throttle up, it begins to move forward, but the treadmill is made to match the forward speed of the plane, only in the opposite direction. So, as the plane moves forward, it moves backwards beneath the aircraft.
In order for the question not to contradict itself, you have to assume that the plane "moving forward" is only
relative to the treadmill. It cannot "begin" to move forward, in
any other sense, if the treadmill is moving backward at the same speed, as stated. What the wheels are doing doesn't matter. How the treadmill works doesn't matter. The stated scenario is that the plane cannot ever move forward because the treadmill moves backward at the same speed -
not the same speed as the wheels, the same speed (realtive to the treadmill) as the whole plane.
You're assuming that, in rotating, the treadmill exerts a backward force on the body of the plane. It's only interacting with the wheels.
No, I'm taking the question literally and establishing the parameters of discussion, to prevent going on irrelevant tangents.
Did my bike example make sense to you?
Yes it makes perfect sense to me, as a description of a bike, a person, and a treadmill.
another way to look at this...
We don't need "another" way. We need to read the question and not add anything to it.
The treadmill is matching the speed of the plane, not the speed that the wheels are turning.
Right. The treadmill is preventing the plane from moving forward because it matches it's forward speed.
Right. The treadmill is preventing the plane from moving forward because it matches it's forward speed.
Why does the treadmill moving backward prevent the plane from moving forward?
Why does the treadmill moving backward prevent the plane from moving forward?
Because it matches its forward speed, as stated. X minus X is zero.
In order for the question not to contradict itself, you have to assume that the plane "moving forward" is only relative to the treadmill.
Nope. That is one interpretation, but that interpretation requires you to assume that planes don't work the way they do. It is not possible for the speed of a treadmill to affect the speed of the plane (short of mechanical failure in the wheels). Therefore, your interpretation is incorrect. You must assume that the plane is moving forward relative to the ground, and the treadmill is moving backward at the same speed, relative to the ground. That is the only physically possible interpretation.
Right. The treadmill is preventing the plane from moving forward because it matches it's forward speed.
Nope, the plane keeps going forward, the treadmill moves backward, and the wheels do double duty.
It is not possible for the speed of a treadmill to affect the speed of the plane (short of mechanical failure in the wheels).
It doesn't have to, and I never said it did. Where did you get that?
You must assume that the plane is moving forward relative to the ground, and the treadmill is moving backward at the same speed, relative to the ground.
If the treadmill matches the forward speed of the plane, the plane cannot "begin" to move forward, except relative to the treadmill.
Because it matches its forward speed, as stated. X minus X is zero.
But the treadmill X can't subtract from the plane's X. The plane still goes X, but the wheels go 2X.
But the treadmill X can't subtract from the plane's X.
It can, because
this question says it can. Start by establishing what is being discussed.
It doesn't have to, and I never said it did. Where did you get that?
When you said that they could cancel each other out. That is not physically possible.
If the treadmill matches the forward speed of the plane, the plane cannot "begin" to move forward, except relative to the treadmill.
The treadmill is moving backward relative to the ground at speed X. The plane is moving forward, relative to the ground, at speed X. The plane is moving at speed 2X relative to the treadmill. Your interpretation is not physically possible.
It can, because this question says it can.
No, it doesn't. We interpret the question differently. Your interpretation is not physically possible, and mine is.
A plane is standing on a runway that can move, like a giant treadmill. When the plane's engines throttle up, it begins to move forward, but the treadmill is made to match the forward speed of the plane, only in the opposite direction. So, as the plane moves forward, it moves backwards beneath the aircraft.
No. It doesn't. All it says is that the treadmill moves backward as fast as the plane moves forward.
Hope this comes through. Never thought I'd see such excitement about a physics problem! :D
That's a nice drawing, but the belt force arrow is in the wrong spot. It applies force to the surface of the weel's tire, not the axle.
Never thought I'd see such excitement about a physics problem!
All the excitement, in this thread, is regarding a
semantics problem.
That's a nice drawing, but the belt force arrow is in the wrong spot.
Which doesn't matter, because the question states what the
result is, not "how" it works.
And the stated result is that the plane moves forward.
Which doesn't matter, because the question states what the result is, not "how" it works.
What? Is this the line you're having problems with?
So, as the plane moves forward, it moves backwards beneath the aircraft.
Because it absolutely does not mean "...as the plane moves forward, the plane moves backwards beneath the aircraft", if that is what you're thinking. Context, man, context.
The question does NOT ask if the belt can move fast enough to keep the plane stationary.
It just says that the belt moves backwards at the same speed as the plane moves forwards. I interpret speed as the movement of something relative to a stationary object, namely the ground.
So if the plane is MOVING (key word folks) forward at 100mph, the belt is moving backwards at 100 miles an hour. The wheels are spinning as if the plane where traveling at 200 miles per hour.
In this interpretation, the plane takes off.
All the excitement, in this thread, is regarding a semantics problem.
OK. If I change the original question to:
"A plane is standing on a runway that can move, like a giant treadmill. When the engines throttle up, the plane begins to move forward, but the treadmill runs at the same speed as the forward speed of the plane, only in the opposite direction. So, as the plane moves forward, the treadmill moves backwards beneath the aircraft.
As the engines throttle up, does the plane take off?"
What would your answer be?
OK. If I change the original question to:
:::stops reading::: I'm discussing the original question.
[SIZE="1"]A plane is standing on a runway that can move, like a giant treadmill. When the plane's engines throttle up, it begins to move forward, but the treadmill is made to match the forward speed of the plane, only in the opposite direction. So, as the plane moves forward, it moves backwards beneath the aircraft.[/SIZE]
Interpretation #1: The plane “begins to move forward” relative to the treadmill, “but” because the treadmill, by whatever mechanism (not stated) moves the same speed, in the opposite direction, the net forward speed of the plane is zero.
Interpretation #2: The plane “begins to move forward” relative to the ground, and the treadmill “match[es] the forward speed of the plane” (relative to the ground) and moves this speed in the opposite direction, causing the wheels to spin faster.
Your interpretation is not physically possible, and mine is.
Can you (or anyone) please elaborate on the reasons why interpretation #1 is not “physically possible”
???
So if the plane is MOVING (key word folks) forward at 100mph, the belt is moving backwards at 100 miles an hour. The wheels are spinning as if the plane where traveling at 200 miles per hour..
The plane is
not moving ith respect to the
AIR, the only substance that matters in this question. No air movement over the wings, no lift, no takeoff. QED.
The question does NOT ask if the belt can move fast enough to keep the plane stationary.
And it doesn’t have to. It states “the treadmill is made to match the forward speed of the plane, only in the opposite direction” so, based on whether you are considering the speed of the plane to be relative to the surface it is on, or relative to the surface
next to the surface it is on, you get either #1 the exact speed needed to keep the plane stationary or #2 a speed completely irrelevant to whether or not the plane is stationary.
This is a wind-up thread based on an unstated distinction which produces two different results.
Can you (or anyone) please elaborate on the reasons why interpretation #1 is not “physically possible” ???
Because the speed of the plane is not determined by its wheels. If you had a treadmill set up according to interpretation one, and the plane was being towed by a truck that was not on the treadmill, as soon as the truck started pulling, no matter how fast the treadmill went, the plane would be pulled forward, because the wheels would just move at the towing speed plus the treadmill speed. And then the magic treadmill would speed up to match that, and the wheels would speed up to match that, etc, etc, and it would rocket up to infinity.
The wheels are unpowered, so they will always spin at the speed of the treadmill (re ground) plus the speed of the plane (re ground). If you then set the speed of the treadmill to match the speed of the wheel rotation, you get a recursive equation. They can't both rely on each other.
Is it the word "but" that confuses? Drop the word "but" in the original question and replace it with the word "and". The conjunction does not change the meaning of the question.
The plane is not moving ith respect to the AIR,
Yes it is. The plane is moving with respect to the air at the speed that its engines propel it. The treadmill is irrelevant. The speed of the treadmill does not affect the forward motion of the plane relative to the air or the ground.
OK, let's try this one. The engine is not on at all. The plane is just sitting there. Now the treadmill/runway starts to turn, let's say at 10 MPH. What happens to the plane?
OK, let's try this one. The engine is not on at all. The plane is just sitting there. Now the treadmill/runway starts to turn, let's say at 10 MPH. What happens to the plane?
Friction or no friction?
OK, let's try this one. The engine is not on at all. The plane is just sitting there. Now the treadmill/runway starts to turn, let's say at 10 MPH. What happens to the plane?
It moves backwards because of friction. The important aspect here is that it takes very little force to overcome this friction because the wheels
roll.
In Steve's scenario, the plane moves along with the runway if there is friction, and it stays stationary if there is no friction.
It's physics class so let's ignore friction. :angel:
It's the old pull-the-tablecloth-out-from-under-the-dishes trick.
Because the speed of the plane is not determined by its wheels.
Forget the wheels.
Wheel speed is not a factor in the original question, so you must assume that it is accounted for, or you are adding extra information.
The conjunction does not change the meaning of the question.
We need to leave the original question alone. But, if we did do what you said, I agree.
The speed of the treadmill does not affect the forward motion of the plane relative to the air or the ground.
But it does, necessarily, affect the speed of the plane relative to
the treadmill (see: Interpretation #1).
OK, let's try this one.
Or, let's just stick to the original question, as stated.
Flint, you make about as much sense as Pie's diagram.
This scientific model is proof it works.From the straight dope:
An airplane taxies in one direction on a moving conveyor belt going the opposite direction. Can the plane take off?
03-Feb-2006
--------------------------------------------------------------------------------
Dear Cecil:
Please, please, please settle this question. The discussion has been going on for ages, and any time someone mentions the words "airplane" or "conveyor belt" everyone starts right back up. Here's the original problem essentially as it was posed to us: "A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?"
There are some difficulties with the wording of the problem, specifically regarding how we define speed, but the spirit of the situation is clear. The solution is also clear to me (and many others), but a staunch group of unbelievers won't accept it. My conclusion is that the plane does take off. Planes, whether jet or propeller, work by pulling themselves through the air. The rotation of their tires results from this forward movement, and has no bearing on the behavior of a plane during takeoff. I claim the only difference between a regular plane and one on a conveyor belt is that the conveyor belt plane's wheels will spin twice as fast during takeoff. Please, Cecil, show us that it's not only theoretically possible (with frictionless wheels) but it's actually possible too. --Berj A. Doudian, via e-mail
Cecil replies:
Excuse me--did I hear somebody say Monty Hall?
On first encounter this question, which has been showing up all over the Net, seems inane because the answer seems so obvious. However, as with the infamous Monty-Hall-three-doors-and-one-prize-problem (see The Straight Dope: "On Let's Make a Deal" you pick Door #1, 02-Nov-1990), the obvious answer is wrong, and you, Berj, are right--the plane takes off normally, with no need to specify frictionless wheels or any other such foolishness. You're also right that the question is often worded badly, leading to confusion, arguments, etc. In short, we've got a topic screaming for the Straight Dope.
First the obvious-but-wrong answer. The unwary tend to reason by analogy to a car on a conveyor belt--if the conveyor moves backward at the same rate that the car's wheels rotate forward, the net result is that the car remains stationary. An aircraft in the same situation, they figure, would stay planted on the ground, since there'd be no air rushing over the wings to give it lift. But of course cars and planes don't work the same way. A car's wheels are its means of propulsion--they push the road backwards (relatively speaking), and the car moves forward. In contrast, a plane's wheels aren't motorized; their purpose is to reduce friction during takeoff (and add it, by braking, when landing). What gets a plane moving are its propellers or jet turbines, which shove the air backward and thereby impel the plane forward. What the wheels, conveyor belt, etc, are up to is largely irrelevant. Let me repeat: Once the pilot fires up the engines, the plane moves forward at pretty much the usual speed relative to the ground--and more importantly the air--regardless of how fast the conveyor belt is moving backward. This generates lift on the wings, and the plane takes off. All the conveyor belt does is, as you correctly conclude, make the plane's wheels spin madly.
A thought experiment commonly cited in discussions of this question is to imagine you're standing on a health-club treadmill in rollerblades while holding a rope attached to the wall in front of you. The treadmill starts; simultaneously you begin to haul in the rope. Although you'll have to overcome some initial friction tugging you backward, in short order you'll be able to pull yourself forward easily.
As you point out, one problem here is the wording of the question. Your version straightforwardly states that the conveyor moves backward at the same rate that the plane moves forward. If the plane's forward speed is 100 miles per hour, the conveyor rolls 100 MPH backward, and the wheels rotate at 200 MPH. Assuming you've got Indy-car-quality tires and wheel bearings, no problem. However, some versions put matters this way: "The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation." This language leads to a paradox: If the plane moves forward at 5 MPH, then its wheels will do likewise, and the treadmill will go 5 MPH backward. But if the treadmill is going 5 MPH backward, then the wheels are really turning 10 MPH forward. But if the wheels are going 10 MPH forward . . . Soon the foolish have persuaded themselves that the treadmill must operate at infinite speed. Nonsense. The question thus stated asks the impossible -- simply put, that A = A + 5 -- and so cannot be framed in this way. Everything clear now? Maybe not. But believe this: The plane takes off.
--CECIL ADAMS
Forget the wheels. Wheel speed is not a factor in the original question, so you must assume that it is accounted for, or you are adding extra information.
No, because wheel speed is identical to the speed of the plane relative to the treadmill. They are the same thing.
But it does, necessarily, affect the speed of the plane relative to the treadmill (see: Interpretation #1).
But the speed of the plane relative to the treadmill does not affect the speed of the plane relative to the ground. The plane's engine does. If the engine is going, then the plane moves forward relative to the ground.
My God I can't believe this problem generated 6 pages of posts.
THE PLANE TAKES OFF!!!!
Flint, you are saying we need to forget HOW a plane works and just assume that because of the word 'but' the plane cannot move forward, even though the question then goes on to say that all the treadmill is doing is matching its speed with the forward motion of the aircraft. Flint, you are correct if this was a car with wings, but because the speed of the ground has no effect on the speed of the AIR around the plane, it will take off normally.
Asking to forget everything about how the objects in question work and make an assumption based on a conjunction in one of the sentences is rediculous, there's no point to even making it a plane at that point then, we can't even assume the wings generate lift because the problem doesn't say that they do.
Flint knows the plane takes off from a "normal" runway treadmill. He's saying this is a special treadmill that somehow holds the plane back. He's deliberately looking for a way to misinterpret the meaning of the question just so he can argue. I don't know if it's face-saving on his part or just bullshitting on the internet. I assume it's the latter.
Pie, compare your diagram to mine in post 67. See the difference? This is critical. The treadmill does not move the axle, it moves the wheel around the axle. Thus, the planes forward thrust has no opposite force, and moves the plane (attached to the axle) forward until lift overcomes gravity and the plane takes off.
This has been fun, but I didn't get a damn thing done this afternoon. We need to add a NSFP* warning on these.
[SIZE="1"]
*Not Safe For Productivity.[/SIZE]
This has been fun, but I didn't get a damn thing done this afternoon.
Alright, mission accomplished! :thumbsup:
Another way to explain it:
There are two sources of force in the system. The plane engine, and the treadmill. The plane engine pushes forward, and the treadmill pushes backward. The wheels of the plane are the interaction between the two forces, and by rotating they allow the engines to move the plane forward and the treadmill to move itself backward without canceling, by rotating at the sum of the two speeds.
Under interpretation #1, the speed of the treadmill is automatically set to equal the speed of the wheels. This is only true if the engines supply no force to the system, but the question precludes that.
This has been fun, but I didn't get a damn thing done this afternoon. We need to add a NSFP* warning on these.
[SIZE="1"]
*Not Safe For Productivity.[/SIZE]
hehehee...I was in meetings most of the day but I checked on this thread a few times. I must say, my head exploded a long time ago. You people be too damn smart for me! :p
It can, because this question says it can. Start by establishing what is being discussed.
This has ceased being a physics discussion and become a semantics issue, hasn't it?
No, because wheel speed is identical to the speed of the plane relative to the treadmill. They are the same thing.
The question does not reference wheel speed, but plane speed. The question is what the plane speed is measured relative to. You can get two different answers, depending on what plane speed is measure relative to.
But the speed of the plane relative to the treadmill does not affect the speed of the plane relative to the ground.
The speed of the plane can be desribed two different ways. They aren't exchangable.
If the engine is going, then the plane moves forward relative to the ground.
The plane isn't on the ground. It's on the treadmill. The treadmill either cancels it’s relative motion, or has no effect whatsoever. See above.
Flint, you are saying we need to forget HOW a plane works and just assume that because of the word 'but' the plane cannot move forward, even though the question then goes on to say that all the treadmill is doing is matching its speed with the forward motion of the aircraft.
No, I’m not saying that. (The forward motion of the aircraft relative to what?)
Asking to forget everything about how the objects in question work and make an assumption based on a conjunction in one of the sentences is ridiculous [sic]…
I'm not asking you to do that.
He's saying this is a special treadmill that somehow holds the plane back.
It doesn't hold the plane back, the plane is moving at exactly the speed the treadmill is moving, in the opposite direction.
The treadmill does not move the axle, it moves the wheel around the axle. Thus, the planes forward thrust has no opposite force, and moves the plane (attached to the axle) forward until lift overcomes gravity and the plane takes off.
The question doesn’t include wheel speed as a variable, only plane speed and treadmill speed.
We need to add a NSFP* warning on these.
[SIZE="1"]
*Not Safe For Productivity.[/SIZE]
No kidding.
Alright, mission accomplished!
The wheels of the plane are the interaction between the two forces, and by rotating they allow the engines to move the plane forward and the treadmill to move itself backward without canceling, by rotating at the sum of the two speeds.
The question doesn’t include wheel speed as a variable, only plane speed and treadmill speed.
Under interpretation #1, the speed of the treadmill is automatically set to equal the speed of the wheels. This is only true if the engines supply no force to the system, but the question precludes that.
No, the treadmill stated in the question only cares about the plane speed, never the wheel speed.
…the treadmill is made to match the forward speed of the plane, only in the opposite direction.
Flint, think about the rotation of the Earth being the same as a giant treadmill, can a plane taking off to the west leave the ground?
Flint, think about the rotation of the Earth being the same as a giant treadmill, can a plane taking off to the west leave the ground?
Q: Does the treadmill have it's own atmosphere?
A: Not as stated in this question.
Good point. The question doesn't clearly state that there is an atmosphere, so a plane wouldn't work anyway. No lift in a vacuum.
The Earth has an atmosphere, the treadmill doesn't, IE, the atmosphere isn't relative to the treadmill, as in 9ths "Earth treadmill" question.
Yes, but the question doesn't state this treadmill is on the Earth, does it?
Umm ... isn't this solely about the action of the plane's engines and the fact that they push air through at great speed (science pushes, but it never, ever sucks:D ), creating air flow over and under the wings, and then the whole Bernoulli effect thing happens, and you get lift? So the treadmill plane should lift off ...
Am I remembering Physics 100 correctly?
otoh, will just the movement of air through the engines provide enough airflow to create sufficient lift for the plane to take off? Normally there's the engine push-through of air plus air passing over/under the wings because the plane is moving relative to the atmosphere - on the treadmill it's not. Will there be enough air moving over the wings to create the needed lift? :confused:
Now if we could just get planes to land on little bitty treadmills, we wouldn't have to build long runways anymore!
Of course not... the air moving across the wing gives lift (a very simplistic description, at-best). The treadmill negates that.
We all have been assuming that the air does not accelerate with the treadmill, which is correct. It is also why the treadmill has no effect. The jet engines push against the AIR, nothing else, so if the air does not accelerate with the treatmill then there must be a constant force pushing back on the aircraft (basic physics). Since the treadmill is only in contact with the wheels, and the wheels cannot transmit a force back onto the aircraft (no brakes being applied), there is an unballenced force acting on the body of the plain. Therefore, the plane must accelerate.
Originally Posted by Happy Monkey
No, because wheel speed is identical to the speed of the plane relative to the treadmill. They are the same thing.
The question does not reference wheel speed, but plane speed. The question is what the plane speed is measured relative to. You can get two different answers, depending on what plane speed is measure relative to.
I didn't say it did. I said that wheel speed is identical to the speed of the plane relative to the treadmill.
[quote]
Originally Posted by Happy Monkey
But the speed of the plane relative to the treadmill does not affect the speed of the plane relative to the ground.
The speed of the plane can be desribed two different ways. They aren't exchangable. [/quote]Again, I didn't say they were. I said that they were different, and that the latter doesn't affect the former.
[quote]
Originally Posted by Happy Monkey
If the engine is going, then the plane moves forward relative to the ground.
The plane isn't on the ground. It's on the treadmill. The treadmill either cancels it’s relative motion, or has no effect whatsoever. [/quote]It cannot cancel the relative motion, because it doesn't apply any force to the plane, just the wheel. The only force pushing the plane is the engine, the engine acts relative to the air, which is not affected by the treadmill. Therefore the plane moves forward relative to the ground.
The question doesn’t include wheel speed as a variable, only plane speed and treadmill speed. No kidding.
...
The question doesn’t include wheel speed as a variable, only plane speed and treadmill speed.
...
No, the treadmill stated in the question only cares about the plane speed, never the wheel speed.
You say that a lot, but it is irrelevant. Wheel speed is equal to the speed of the plane relative to the treadmill. They are identical.
Of course not... the air moving across the wing gives lift (a very simplistic description, at-best). The treadmill negates that.
It would if it kept the plane stationary relative to the ground, which it can't.
Jet engines don't push against the air, they push against the plane. The plane will be pushed forward until it reaches takeoff velocity, no matter what speed the wheels are turning. All they do is keep the plane from dragging on the ground. Planes take off from runways that are moving at 1000 mph, under them, every day. ;)
The answer to why manholes are round? Because men are round. Duh
So a man can tip open a lid that would be to heavy to lift.
9 pages on topic, impressive. Unless the runway is moving air, you've got nothing but a over-powered paper weight.
I changed my mind. Bruce is right; the jet engines aren't pulling air over and under the wings; in fact, the engine doesn't even have to be on the wing. The engines are pushing the plane to achieve atmospheric air flow over and under the wings. Since the treadmill plane isn't moving relative to the atmosphere, the needed air flow around the wings doesn't happen and there's no lift; just a lot of engine revving and wheel-spinning. It doesn't matter what 'ground speed' the instruments record, the plane has no velocity relative to the air around it. The thing won't fly, any more than a kite will fly if you hold its string while running on a treadmill.
That's my story, and I'm stickin' to it. :p
and it keeps the covers from falling down into the sewers
*pokes head into room.....realises is totally out of depth and retreats*
But the engines still exert a force against the body of the aircraft, and since the runway can't exert any force in the absence of friction, their is a net acting force on the aircraft
and it keeps the covers from falling down into the sewers
Yes, I forgot that important part. :thumb:
snip~ Since the treadmill plane isn't moving relative to the atmosphere, the needed air flow around the wings doesn't happen and there's no lift; just a lot of engine revving and wheel-spinning.
~snip :p
Nope, the engines push the plane through the atmosphere (air), and what the ground and wheels are doing under it has absolutely no bearing on the plane moving through the air. Up she goes, into the wild blue yonder. Flying high, into the sky. :cool:
Nope, the engines push the plane through the atmosphere (air):
That's just what the engines
don't do in the case of the treadmill plane. They aren't moving it through the atmosphere. It's stationary with respect to the air around it, therefore no flow, therefore no lift.
If you run on a treadmill, does air flow past your face (assuming no fan!)?
The riddle/question is on every other forum. I figure I should bring the torture here, as well.
A plane is standing on a runway that can move, like a giant treadmill. When the plane's engines throttle up, it begins to move forward, but the treadmill is made to match the forward speed of the plane, only in the opposite direction. So, as the plane moves forward, it moves backwards beneath the aircraft.
As the engines throttle up, does the plane take off?
Oh, Kay....but where in the original post does it say that this hypothetical plane...has wings?
The plane isn't running on a treadmill, that's not how it moves. It moves by pushing through the air...the treadmill has no bearing on the plane. :headshake
Good point. The question doesn't clearly state that there is an atmosphere, so a plane wouldn't work anyway. No lift in a vacuum.
Nor combustion w/o supplied oxygen.
Another example of the unimportance of wheels relative to a plane's taking off.
Ski planes and water planes have no wheels, hell, if a plane were lying on its belly on a greased treadmill it would take off.
...but the treadmill is made to match the forward speed of the plane, only in the opposite direction. So, as the plane moves forward, it moves backwards beneath the aircraft.
There are two interpretations for this. Both are possible, but neither is specified by the provided information.
#1: If the "forward speed" is defined as relative to the treadmill then the plane is stationary relative to the air.
#2: If the "forward speed" is defined as relative to the ground, then it is possible for the plane to be in motion relative to the air.
Nothing in the question rules out either of these interpretations, and no amount of blustery hoopla or physics masturbation can change that.
The question is unanswerable as stated. It's designed that way on purpose.Pie, compare your diagram to mine in post 67. See the difference? This is critical. The treadmill does not move the axle, it moves the wheel around the axle. Thus, the planes forward thrust has no opposite force, and moves the plane (attached to the axle) forward until lift overcomes gravity and the plane takes off.
Okay, this is the absolute last post I'm going to make on this subject. (promise!) If the wheel experiences a force, that force
must be transmitted to the axle. (The other alternative is that the wheel goes that-a-way while the rest of the plane stays put.) The free body diagram holds.
The straight dope misses this point:
A thought experiment commonly cited in discussions of this question is to imagine you're standing on a health-club treadmill in rollerblades while holding a rope attached to the wall in front of you. The treadmill starts; simultaneously you begin to haul in the rope. Although you'll have to overcome some initial friction tugging you backward, in short order you'll be able to pull yourself forward easily.
That "pull yourself forward easily" is impossible. To move yourself forward at all (even a micron per hour) still necessitates a net imbalance in the forces acting on the axle of the wheel; this is patently impossible, given the wording of the problem. F1 == F2
by the very statement of the scenario, so no net motion.
Newton would be scratching his head.
I'm with Flint and Pie. I wholeheartedly agree that, IF THE PROBLEM WAS REALISTIC AND SAID WHEEL SPEED, NOT PLANE SPEED, it would definitely take off. But the problem doesnt say that. It's unanswerable, because plane design + physics =/= the actual problem.
The answer to the original question is no.
I took aerodynamics in high school and even though I squeeked by with a D due to a terrific Huey camofluage model I made I did learn something and that is a plane needs lift to fly.
Since ditching my flying career I have forgoten the little I did learn so
I went and made sure so I found proof.
Straight and Level Flight
In order for an airplane to fly straight and level, the following relationships must be true:
Thrust = Drag
Lift = Weight
If, for any reason, the amount of drag becomes larger than the amount of thrust, the plane will slow down. If the thrust is increased so that it is greater than the drag, the plane will speed up.
Similarly, if the amount of lift drops below the weight of the airplane, the plane will descend. By increasing the lift, the pilot can make the airplane climb.
http://travel.howstuffworks.com/airplane1.htmA plane is standing on a runway that can move, like a giant treadmill. When the plane's engines throttle up, it begins to move forward, but the treadmill is made to match the forward speed of the plane, only in the opposite direction. So, as the plane moves forward, [treadmill] moves backwards beneath the aircraft.
First - what is the purpose of wheels (landing gear)? So that velocity of a plane is totally irrelevant to ground. Wheels will spin as slow or as fast as necessary so that velocity of the runway and velocity of plane stay totally independent.
Second - plane's velocity is determined by a force applied between plane and air. As engine force increases, then airplane acceleration (and therefore velocity) is according to the well known F=ma equation. Engine force determines airspeed - a relationship between plane and air.
Meanwhile, what do wheels do? See point first. They spin as fast as necessary so that plane's velocity is irrelevant to (independent of) earth.
Since air and runway remain at same location, then plane's velocity to air is same as plane's velocity relative to runway. Therefore wheels spin at plane's airspeed which is same as runway speed.
In this problem, we have added something unique. Runway is replaced by a treadmill. As plane moves forward 1 MPH (relative to air as in point second) then treadmill moves 1 MPH in reverse. Again, wheel's job is to keep airplane and runway completely separate (point first). Therefore wheels must now spin at 2 MPH to keep treadmill and plane independent of each other.
If wheels applied the "F=ma" between plane and runway (as in a car or bicycle), then wheels and ground would not be independent. But wheels do not move this plane. Motion is created completely by a relationship between air and plane - its jet engine. No matter how fast ground moves, plane's velocity (and acceleration) is only based upon F=ma between plane and air. No matter how fast ground moves, wheels will spin as necessary to keep treadmill and plane completely independent of each other.
Now we address other possible (and unstated) references.
Since treadmill will always move backwards (relative to air) at the same speed that plane moves forward (relative to air), then wheels will spin at twice the airspeed.
Treadmill is set to match forward airspeed. Relative to what? If treadmill's speed is relative to air and plane's speed is relative to air, then wheels spin at twice airspeed. But if treadmill's speed is relative to plane, then treadmill never moves relative to air. Now we have wheels only moving at one times airspeed.
One fact we do know. Airplane's speed is always relative to air because those engines create a relationship only between air and the plane. Treadmill's speed (in this problem) could be relative to air or relative to plane. But again, point first - those wheels always make ground independent of the plane. Wheels will always spin as slow or fast as necessary so that plane and earth velocities do not affect each other.
The initial premise is flawed, implying that moving the surface the plane rests on can keep the plane from moving forward or have some kind of influence over the lift achieved by the lifting surface of the plane.
As we have seen ad nauseum, the resting surface has no effect on the forward motion of the plane. Rather, the moving treadmill will make the wheels turn faster while the plane will move forward as it would normally at any given engine setting. If the forward motion of the plane where to be inhibitted (sp?) or restrained somehow so as to prevent adequate airflow over the lifting surfaces then the plane will not fly. If the plane is stationary, yet somehow adequate airflow is achieved over the lifting surfaces then the plane will fly.
Both sides of the discussion so far seem to me to have made these points but without noting the flaw in the initial premise.
If you could use this logic to launch a plane, then tell me why the navy hasn't exploited it yet?
I posted this after the hall of fame post. Maybe I should now delete that one...or maybe I just can't be arsed in the end.
They usually do. Only occasionally does the Navy launch planes illogically.
Oh, wait... Bush..... um.... nevermind. :o
If you could use this logic to launch a plane, then tell me why the navy hasn't exploited it yet?
I posted this after the hall of fame post. Maybe I should now delete that one...or maybe I just can't be arsed in the end.
I believe that the navy's catapult system is an application of this logic: a very short takeoff that achieves adequate airflow over the wings so as to allow the plane to fly.
Now i must look for hall of fame post referenced above,,,
The question is unanswerable as stated. It's designed that way on purpose.
Yes, the person that wrote the question (not necessarily the OP) Is either brilliant, or a total idiot.
I still interpret it to scenario #2. Wherein movement means movement relative to an outside observer of the equation, i.e. someone standing on the ground off the treadmill and not in the plane.
Was that what the question asked? Hard to say. We all (or at least 99% of us) know that a plane will not take off if it does not move through the air. The jets or prop do not provide the lift, they only provide the forward momentum.
Yes, the person that wrote the question (not necessarily the OP) Is either brilliant, or a total idiot.
I'm voting for "brilliant idiot".
My opinon of a lot of posters' intelligence has been confirmed by some of the posts on this thread.
Perhaps some folks will find it enlightening to hear about the time I did an engine run-up before departure on an ice-covered runway at Hazelton, PA. (The ice serving as a pretty fair analog of the aformentioned conveyor.) Engine run up involves locking the brakes and applying something close to crusing power to make sure the engine is running OK...and also involves testing other things that need to work when the engine is at cruise, like making sure both sets of magnetos are firing plugs, that the auxiliary fuel pump pumps fuel, that the prop pitch control controls the prop pitch, the vaccum pump pumps vacuum...I mean air...etc.
Anyway, usually you lock the brakes and apply power, engine revs up and various needles move as appropriate...and nothing else happens. In this case, the tire s had very little friction on the runway (well, taxiway, this was) and started moving forward, much to my chagrin, as I was not quite ready to get out on the runway yet.
So that day I took off without a runup...since I couldn't actually do one.
If I'd been lined up with the runway, had advance the thrust to full power, and had used a little bit of extra runway length to allow for the small amount of friction there was, I woudl have ended up flying without ever releasing the brakes.
It's all about the air moving past the wings...and the engine thrust will most assuredly move the airplane through the air quite handily unless something prevents it...like friction in the brakes and of wheels against dry pavement.
I still want to see experiments with a real treadmill... Bruce, surely your employer has some facilities? At least they could supply a couple spare planes they don't need anymore for testing purposes! :rolleyes:
I've never heard this before. But no, a plane takes off because its wings generate lift, which it can only do when moving forward.
UT got it right first.
http://travel.howstuffworks.com/airplane4.htm
A Few Words About FluidAs we mentioned, a principal concept in aerodynamics is the idea that air is a fluid. Like all gases, air flows and behaves in a similar manner to water and other liquids. Even though air, water and pancake syrup may seem like very different substances, they all conform to the same set of mathematical relationships. In fact, basic aerodynamic tests are sometimes performed underwater.
Another important concept is the fact that lift can exist only in the presence of a moving fluid. This is also true for drag. It doesn't matter if the object is stationary and the fluid is moving, or if the fluid is still and the object is moving through it. What really matters is the relative difference in speeds between the object and the fluid
There are two interpretations for this. Both are possible, but neither is specified by the provided information.
#1: If the "forward speed" is defined as relative to the treadmill then the plane is stationary relative to the air.
#2: If the "forward speed" is defined as relative to the ground, then it is possible for the plane to be in motion relative to the air.
Nothing in the question rules out either of these interpretations, and no amount of blustery hoopla or physics masturbation can change that.
The question was written from the point of view of an observer, right? That observer is the one doing the measuring of the forward speed. It's forward speed relative to the observer.
That observer could be:
1. standing on the ground,
2. floating in the air,
3. standing on the treadmill, or
4. sitting in the plane
1&2: If the "forward speed" observer were in situation 1 or 2, the question would be written as it is, and the forward speed of the plane would be measured relative the the observer, which is the same as the ground. This would be your interpretation #2. It's how I and most here read the question.
3: If the observer is standing on the treadmill (3), he/she would have the perspective of the treadmill. If the treadmill starts moving, the observer won't feel motion because they are attached to the treadmill, They will feel a tailwind. Since the observer is writing the question, the question would be about planes taxiing in tailwinds, not about moving runways. The question doesn't mention winds anywhere, so the question is not from the point of view of the treadmill, and the plane's forward speed is not measured from that reference. Your interpretation #1 above is not a credible interpretation of the question as written, because nowhere does the question mention wind. Wind is not a part of the question, and the question does not mention wind. While this post may contain wind, there is none in the question.
4:Finally, if the observer is in the plane, he/she will see both the ground move and the runway move even faster. I don't think anyone believes this is written from the point of view of the plane, so I won't go into it further.
The question does not define "forward speed" in a way that makes the question answerable.
The question does not define "forward speed" in a way that makes the question answerable.
Maybe not for you, but it's clearly written from the point of view of an observer standing on the ground, otherwise it would talk about wind.
What has Occam's Razor got to do with this situation?
There is no wind in the question, so it's written by an observer on the ground.
Uh guys, there's no point in debating it. That plane is long gone.:rolleyes:
What has Occam's Razor got to do with this situation?
Not making unwarranted assumptions or adding extra information.
The question does not define "forward speed" in a way that makes the question answerable, and you can't make it so, without going outside of what is stated. (See: most of this thread.) Step #1, often overlooked, is to read the question and establish what is being discussed. In this case, you can't - the question does not contain the information. Any attempt to re-write the question means you are not answering the original question.
I owe you an apology. You did note the flaw in the original premise and i missed it. Please excuse me.
I used to be friends with this guy, Scott. He was always right, no matter what, and if it looked like he was wrong he'd press the issue until he was right, in some sense. Any sense.
One day we're driving through Atlantic City and we realize we need to turn right to get to where we wanted to go.
Scott: Turn here!
UT: No, it's one-way.
Scott: No, that's two-way.
UT: I saw the sign.
Scott: That couldn't be.
UT: And there was no turning lane.
Scott: Maybe it was taken up by a double-parked car.
UT: Dude, I'm sure of it. I'm driving. I'm paying more attention to all the signs and the road.
Scott: But maybe I'm paying more attention because I don't have to drive!
UT: OK, here's the next crossing street, I'll turn right here, and then I'll turn right again and we can take a look at the street.
Scott: Done!
UT: OK... yep, there's the sign.
Scott: Oh. Hrm. Hmmm. But look - that doesn't look one-way there. You see, don't you, how I could have made that mistake? There's a solid line down the middle of the street. And the whole thing is not very clearly marked. They use terrible signs here. In fact, I think it used to be a two-way street and they just made it one-way. It looks like that car is parked in reverse. You see, don't you? Anyone would have thought that was two-way.
The question states the plane moves forward and the ground(treadmill)moves backwards. When you throttle up the plane will take off. The only assumption is the plane is capable of flying in the first place. :eyebrow:
I'm gonna guess this former friend was/is single:D
"moves forward"
Relative to what? Not stated.
The former friend who was so certain of everything, became uncertain that he was male. He had a sex-change operation and yes, remains single, although she dropped the personality trait of certainty somewhere along the way.
Many of us find humility at some point in our lives. Some of us find it harder than others.
Relative to what? Not stated.
Relative to the same observer who sees the treadmill moving. If the observer sees the treadmill moving, he isn't on it.
Many of us find humility at some point in our lives. Some of us find it harder than others.
I'll try to remember this.
Now I'm sorry I made a joke about that friend. :blush:
Relative to the same observer who sees the treadmill moving.
This isn't a first person account of an actual event, it's a hypothetical. It could just as likely be written from an omniscient perspective, as the events described are not actual events. The question doesn't make this distinction, so you can't. If you re-write the question, you're no longer answering the question.
You mentioned Occam's razor before. Is it simpler to have one point of view of both the plane and treadmill, or is it simpler to have a point of view that is jumping all over the place?
Consider that the one point of view keeps the question clear, and the multiple points of view or omniscient point of view muddies the meaning of the question.
How does Occam's Razor apply here?
Relative to what? Not stated.
If it's not stated, then it's relative to where it was and nothing else.:cool:
Is it simpler to have one point of view of both the plane and treadmill, or is it simpler to have a point of view that is jumping all over the place?
It is simpler to have one point-of-view. But the question doesn't state which one. It's unanswerable.
"forward speed"
Relative to what? Not stated.
If it's not stated, then it's relative to where it was and nothing else.
The surface it's on, or the surface
next to the surface it's on? Not stated.
It is simpler to have one point-of-view. But the question doesn't state which one. It's unanswerable.
OK. It's simpler to have one point of view.
Are you saying the question is written from one single point of view?
No, if it's not stated you can't chose what to relate it to, that's adding to the question. It can only be relative to where it was if it moved, which the question states it did. :litebulb:
"where it was"
It was on the treadmill.
Are you saying the question is written from one single point of view?
Ask the question. The point is: The question can only be what it is, nothing more.
It dosn't matter what the speed is because it is 'matched' by the treadmill. There is an equal and opposite momentum.
That's what the question said.
...> It the treadmill is made to match the forward speed of the plane, only in the opposite direction.
The question does not define "forward speed" in a way that makes the question answerable.
It doesn't have to. Only one of the interpretations is physically possible. Reality isn't an additional assumption.
Only one of the interpretations is physically possible.
The question doesn't ask you to explain how the hypothetical treadmill accomplishes what is stated.
Occam's razor.
I choose not to include a magic treadmill.
As Flint is saying, there are two different ways to look at the problem. I think that scenario #1 is difficult to achieve in the real world.
Scenario #1 is not possible. That is something that you have to factor in to the question. Like a math proof, if you follow one assumption, and it leads to a contradiction, you can eliminate that possibility.
I choose not to include a magic treadmill.
...Dear Cecil:
...
Ok, first of all, don't ask Cecil. Beanie may know the answer, but Cecil won't
Now, concerning Labrat's ass ... I mean bicycle analogy, one thing is missing. The airport moving walkway would speed up to counteract the push that you give the bike.
I'm so out of this thread once it passes the 200th post. mark my words.
I'm so tempted to make six consecutive posts, but I'll be nice and leave it at one.
Now, concerning Labrat's ass ... I mean bicycle analogy, one thing is missing. The airport moving walkway would speed up to counteract the push that you give the bike.
No it can't. The only thing the runway can do is speed up the wheels. A push will still move the bicycle forward.
I'm so tempted to make six consecutive posts, but I'll be nice and leave it at one.
I was expecting someone to do that. You surprised me, Mr. Dallas, with your restraint. Unlike the treadmill, which provides no restraint for the plane.
Unlike the treadmill, which provides no restraint for the plane.
Now, concerning Labrat's bicycle analogy, one thing is missing. The airport moving walkway would speed up to counteract the push that you give the bike.
Yeah, and in doing so, make the wheels turn faster. But the bike would keep on keepin' on with you pushing it.
Here is something you
can test--if you're near a large airport.
If you are pulling one of your airport bags with the wheels on it down the airport terminal, then walk onto (or next to with the bag still on the thingie) a moving walkway thingie, and continue to walk at the same speed what happens? The bag does not stop moving because the tread underneath it is going in the opposite direction. It continues forward because YOU are pulling it, while the wheels spin faster than they were when they were on solid ground. You=the plane's thrusters. the bag = the plane on wheels.
TRY IT!!!!!!!
And with that, this thread is finished :)
Can the treadmill possibly exert enough force on the plane to counteract the force of the thrust?
1) Pie is correct that any force exerted on the wheels is subsequently exerted on the plane (although LabRat's drawing is better).
2) By SteveDallas' example, we know that
Fthrust => Ftreadmill
otherwise the plane would be pushed backwards. If Fthrust > Ftreadmill, the plane must accelerate forward and then eventually take off.
3) The force exerted by the treadmill on the wheels is a friction force, and therefore limited to:
Ftreadmill <= μR * Weight of plane
Where μR is the coefficient of rolling friction.
There are three different coefficients of friction that we could use: static, rolling, and kinetic. Static means that the plane is not moving at all w/r to the treadmill. With kinetic friction, the plane and the wheels are sliding forward, as in Maggie's story of brakes on ice.
μK < μR < μS
I'm not sure what the coefficient of rolling friction is for a 747, but the
largest μR listed on Wikipedia is 0.03, and that's for a bus on asphalt. I assume that μR for a plane would be much smaller, but I'll use 0.03 for effect. According to
Boeing's site, for a 747-400, the maximum takeoff weight of the plane is 3886 kN. Each of the 4 engines produces a maximum of 281 kN of thrust, for a total of 1124 kN of thrust.
So
Ftreadmill <= 3886 kN * 0.03 = 116.6 kN
Fthrust = 1124 kN
1124 kN > 116.6 kN
I'm not entirely sure, but it looks like this plane is going to move forward, and the treadmill can't go fast enough to stop it, because the plane will just start sliding. Since the plane is moving forward, air goes over the wings, and the plane takes off.
Can anyone get μR for a plane wheel?
No it can't. The only thing the runway can do is speed up the wheels. A push will still move the bicycle forward.
Nuh-uh.:p
And with that, this thread is finished :)
/me didn't get the memo in time
...TRY IT!!!!!!!
Woops! The walkway doesn't speed up. :redface:
The wheels effectively disconnect the plane from the treadmill. the movement of the plane is relative to the planet they are both sitting on. the treadmill can spin any direction and rate you want it to and will have _no_ effect on the airplane or it's ability to move forward at an increasing rate and eventually generate enough lift to fly.
TRY IT!!!!!!!
Interpretation #1: The question doesn't allow you to move forward, relative to the treadmill.
Interpretation #2: The question does allow you to move forward, relative to the treadmill.
Interpretation #3: In this variation of Interpretation #1, you
slide forward, relative to the treadmill.
...the treadmill can spin any direction and rate you want it to and will have _no_ effect on the airplane or it's ability to move forward...
It has exactly that effect, if you interpret the question as stating that the plane's forward motion is relative to the treadmill.
But now aren't we back to the flaw in the premise?
aren't we back on the treadmill?
aren't we back on the treadmill?
Nope -- landing is an entirely different problem.
aren't we back on the treadmill?
We're running a rat race on a treadmill with a LabRat
By the way, the question doesn't say it's a jet.
Just as it doesn't say the planes movement is relative to any thing.:p
I believe that the navy's catapult system is an application of this logic: a very short takeoff that achieves adequate airflow over the wings so as to allow the plane to fly.
Airplane on a catapult has zero relation to his problem. F=ma . Plane must have sufficient "a" to achieve airspeed on a short runway. Planes engines do not provide enough '"F" . So catapult adds more "F" . Carrier planes are catapulted on a runway (not a treadmill) as defined by numbers in
post 152 .
The question was written from the point of view of an observer, right? That observer is the one doing the measuring of the forward speed. It's forward speed relative to the observer.
That observer could be:
1. standing on the ground,
2. floating in the air,
3. standing on the treadmill, or
4. sitting in the plane
We simply do the answer as demonstrated in
post 152 and then change the answer to that 'observers' reference.
We do same thing with electricity. Which is ground? Earth? Breaker box? Computer motherboard? Any one can be ground. We can define any point as the reference point. We select any reference point only to make the problem easier to solve. Same applies to this problem.
We have three possible 'grounds' - points of reference. Four if we complicate the problem by considering an observer. The observer is completely unnecessary to the question - airspeed - velocity between airplane and air.
Air is a perfect reference point because a clearly defined relationship exists between air and the plane.
When the plane's engines throttle up, ...
And we have a known relationship between air and the runway or treadmill. Break a problem into parts. We do all numbers relative to air AND therefore have a simple answer.
Obviously - and this is just too simple for all the speculation - obviously -As the engines throttle up, the plane does take off whether it is on a runway or on a treadmill. Obviously because what the treadmill does is completely irrelevant to (independent of) airplane and air. Obviously plane's airspeed only involves a relationship between air and airplane. Obviously observer’s location and what treadmill does are completely irrelevant. Obviously wheels make that treadmill movement completely separate of (independent - not connected to) airplane and air. Obviously location of observer is completely separate from (independent of) airplane and air.
It is quite scary that so many cannot grasp these obvious and simple relationships. Some of these replies are making me feel like a genius. That scares me.
The question does not define "forward speed" in a way that makes the question answerable.
J Just because they did not tell you which to use as the reference point, then you cannot arbitrarily choose one? Nonsense. See the previous post. Choose air as the reference point. As engines throttle up, velocity of air to airplane increases until takeoff speed is achieved. All this occurs regardless of runway, treadmill, or catapult.
Engine defines a relationship between airplane and air. That makes the problem simple and completely solvable (once we include numbers for engine force, plane mass, and minimum speed for takeoff). It's just not that complex. This is a trivial high school physics problem where a runway / treadmill is completely irrelevant.
So many unable to grasp this so simple problem is scary.
The question does not define "forward speed" in a way that makes the question answerable, ...
Of course it does.
When the plane's engines throttle up, it begins to move forward,
The classic F=ma relationship and the classic v=ma . Foreward speed is defined once we have numbers for these simple equations. And again, treadmill and observer will only confuse one with irrelevant parameters.
Clearly this problem has so confused so many and yet no one has yet asked about landing. Are there terrorists among us?
Just another reference point to keep us confused.
Of course it does. The classic F=ma relationship and the classic v=ma .
the classic v = ma? I'm not familiar with that one. Are you confusing yourself with v=at or p=mv?
Just because they did not tell you which to use as the reference point, then you cannot arbitrarily choose one? Nonsense. See the previous post. Choose air as the reference point.
The problem is not explicit, therefore you must do whatever tw tells you to do.:right:
Airplane on a catapult has zero relation to his problem. F=ma . Plane must have sufficient "a" to achieve airspeed on a short runway. Planes engines do not provide enough '"F" . So catapult adds more "F" . Carrier planes are catapulted on a runway (not a treadmill) as defined by numbers in post 152 .
But the force here is relevant only so far as it contributes to air moving over the airfoil, no? So the movement of the treadmill, not contributing any positive or negative to getting air moving about the airfoil, contributes nothing, either positive or negative to the ability of the plane to fly.
I think.
Just because they did not tell you which to use as the reference point, then you cannot arbitrarily choose one?
Depending on what you interpret the plane's forward motion as being relative to, you get a different answer.
Some of these replies are making me feel like a genius.
The question is designed to make you feel like a genius. But, I'm sure you're the one who finally found the "right" answer, huh?
I used to be friends with this guy, Scott. He was always right, no matter what, and if it looked like he was wrong he'd press the issue until he was right, in some sense. Any sense.
Oh, my dear Ghod...and you know what? That person's not much different today. :-)
At least in that respect. :-)
[SIZE="1"]What TW Meantto say[/SIZE]
It's George Jr's fault...mental midget....seven seconds... top management... limbaugh disciples... no WMD...
The original question says the treadmill matches the planes speed. It cancels out. The plane isn't moving forward to create airflow over and under the wings so it isn't going to fly.
That is actually good to hear. I always felt like she lost some of her personality through the transition. Like Scott would push back, but Lisa wouldn't. I liked that push back sometimes.
As long as the "it won't fly" people are continuing to be maroons, let me point out that an airplane sitting on the runway with the engine *off* (or with no engine at all) will take off all by itself if the wind speed exceeds the stall speed. This is why we tie aircraft down: wheel chocks aren't sufficient in the case of a lightly wing-loaded aircraft in the presence of a stiff breeze.
With sufficient wind speed, an airplane can take off (or be landed) with *zero* forward motion relative to the ground. There's a standard airshow demo that's done in STOL-type airplanes (Piper Cub, or maybe a Maule or Zenith CH-701) that involves hovering and even flying backwards when the wind speed is high enough.
Any attempt to re-write the question means you are not answering the original question.
[SIZE="1"]What TW Meantto say[/SIZE]
It's George Jr's fault...mental midget....seven seconds... top management... limbaugh disciples... no WMD...
Ya forgot MBAs that ordered that stupid treadmill. ;)
Maggie, The original question dosn't say the wind speed exceeds the stall speed.
i read the question....thought about it..decided that the rotation of the wheels nullified the movement of the treadmill..then i decided to wait to see what Happy Monkey would say, and knew i was right when he agreed.
the only way this scenario works out to no forward movement, and thence no lift is if the wheels are locked, and fastened tight to the surface.
as happy monkey said. it's a trick question
That is actually good to hear. I always felt like she lost some of her personality through the transition. Like Scott would push back, but Lisa wouldn't. I liked that push back sometimes.
Oh, Lisa's still the same person, no question about it. I think it's natural to lose some assertiveness during transition--especially male to female--because that power is being consumed elsewhere. But then begins the process of integrating core motivations with a new set of social expectations and norms. The strategy is largely unchanged, but often the tactics are different. Learning the new tactics isn't instantaneous.
One of the cruelest things that happens to a transitioning transsexual is the important people in your life who find it easier to cope with your transition by behaving as if the person they knew is now dead; taken over zombie fashion by some other entity. In the cases I know, t'aint so.
you said taint
NOW the plane/treadmill debate is OVER!
Maggie, The original question dosn't say the wind speed exceeds the stall speed.
No, it doesn't. But I'm trying to shed light on the fact that lift is a function only of airspeed (and angle of attack). Groundspeed is irrelevant, and airspeed and groundspeed are two different things.
The other thing that some folks are missing is that airspeed is created by thrust...and that the operation of thrust has nothing to do with the ground or how the airplane is supported before takeoff (wheels, treadmills, skis, skids, floats, etc.) at all.
If thrust had anything to do with the ground, it wouldn't work while flying. Duh.
you said taint
"taint" != "t'aint", just as "wont" != "won't"
The original question says the treadmill matches the planes speed. It cancels out. The plane isn't moving forward to create airflow over and under the wings so it isn't going to fly.
it doesn't matter that the treadmill matches the planes speed. The wheels aren't driving the plane. The treadmill will only affect the rotation of the wheels, which will only affect the movement of the plane if the brakes are applied and the surface of the treadmills won't allow a skid. In which case the tires will eventually blow and the plane will skid on it's rims.
The treadmill can make the wheels be still by matching the forward movement of the plane. it can make the wheels roll backward while the plane moves forward by moving faster than the speed of the plane. it can make the wheels move forward by moving slower than the speed of the plane. But until the plane becomes a car with a drive shaft mechanicallly linked to the engines the movement of the wheels will have no effect on the movement of the plane.
I guess I am just too stupid to get it then. Thanks hideouse. You tried. :)
I guess I am just too stupid to get it then. Thanks hideouse. You tried. :)
It's very counterintuitive if the only wheeled vehicles you've ever been in moved by applying power to the wheels. But imagine an airboat in a swift current...the propellor operates on the air, not on the water.
Someday come along with me for a ride in the Cardinal...feeling it happen makes a difference.
I used to be friends with this guy, Scott. He was always right, no matter what, and if it looked like he was wrong he'd press the issue until he was right, in some sense. Any sense.
...
Is his name now MaggieL?:p ;) :D
Is his name now MaggieL?:p ;) :D
Nope. Read your Cellar history.
Eppur si muove.I guess I am just too stupid to get it then. Thanks hideouse. You tried. :)
You are a good sport Sky.:)
it doesn't matter that the treadmill matches the planes speed. The wheels aren't driving the plane.
The question states that the treadmill matches the plane's speed. Wheels be damned. If you believe the question, you believe the treadmill matches the plane's speed, regardless of what the wheels are doing. The question is: what is the plane's speed relative to? And this information is not provided. It's only a trick question in the sense that it tricks you into thinking there is any determinable answer. As it is stated, there isn't.
It's very counterintuitive if the only wheeled vehicles you've ever been in moved by applying power to the wheels.
I don't think anyone in the history of this question has ever thought that the wheels are the source of propulsion for the plane. Also, I don't think anyone has ever thought that a plane can take off without air moving over the wings. The question is designed to get groups of people arguing about two completely different scenarios, and these non-points are inherent in the comparison between the two. Based on what you believe the question is stating as the premise (which isn't specified), there are two different outcomes. There is no "right" answer.
yes there is.
dude.
if the plane is going 100 mph, and the track of the treadmill is also going 100mph.....then the plans'e wheels are going 100 mph......but they have no effect on the plane's speed because they rotate
Uh, wheels = 200, Jim.;)
The question was written to lead people into the wrong logic, rather than discarding superfluous information. It is a trick question, but there still is one right answer..... and many wrong answers.
"forward speed" relative to what? Not stated.
Of course, in #3 the plane can slide into forward motion, but that isn't necessary unless in addition to #1. In #2 it just takes off.
Uh, wheels = 200, Jim.;)
The question was written to lead people into the wrong logic, rather than discarding superfluous information. It is a trick question, but there still is one right answer..... and many wrong answers.
rotating 200 mph, yes. moving 100 mph as the plane carries them
relative to the earth, flint, as everything is.
I don't think anyone in the history of this question has ever thought that the wheels are the source of propulsion for the plane.
Nor did I say that. I said that if you'd only been in powered-wheel vehicles the situation was counterintuitive.
Oh, by the way:
an airplane that generates some lift in an unorthdox wayNOW the plane/treadmill debate is OVER!
This is the internet. It's not over until somebody says something about Hitler and you know it.
Oh, crap. I just blew my nomination for the Hall of Fame. Is a non-productive contribution to the thread still counted as a contribution?
wow, maggie.
here's more
why aren't these designs being applied to other aircraft?
It's George Jr's fault...mental midget....seven seconds... top management... limbaugh disciples... no WMD...
George Jr is the observer? No wonder an accurate answer is not possible!
This is the internet. It's not over until somebody says something about Hitler and you know it.
Oh, crap. I just blew my nomination for the Hall of Fame. Is a non-productive contribution to the thread still counted as a contribution?
And you mentioned Hitler in the same post! Double whammy.
"forward speed" relative to what? Not stated.
The speed is obviously defined by this:
When the plane's engines throttle up, it begins to move forward,
Again, a reference to the equations F=ma and v=at . Speed does not exist on its own. Speed is a relationship between two references. Force (the "F") defines those two refeneces. Engine creates a force between airplane and air. Therefore speed is also created / measured between airplane and air. "Forward speed" is defined by that phrase
When the plane's engines throttle up, it begins to move forward,
Previously posted are the numbers to stick into those equations so that we know how long (t time) that engine (F force) must push the plane (m mass) to obtain minimum takeoff speed (v speed).
how fast would a standard jet have to turn it's engines in order to pull enough wind over its wings to generate lift? assuming it stood still relative to the ground?
They are mounted under the wing, so they couldn't do what you describe. The airflow has to be above the wing.
the air has to go faster above than below, so the engine position below the wing prevents that from ever happening. right on
why aren't these designs being applied to other aircraft?
Well...it looks gooofy, and aviators can be surprisingly conservative. The engineering of it is tricky...I suspect the wing shape has a weight penalty. And once you're airborne there's usually plenty of lift available, as long as you're willing to trade it for induced drag.
It's a rockin' performer on takeoff, but I bet the efficiency blows dead goats in cruise. Nonetheless, Custer apparently sued Fairchild claiming the A-10 Warthog violated his patent.
By the way,
The MidAtlantic Air Museum at the Reading Airport has a Channelwing...not currently flyable.
..not currently flyable.
... as it was mistakenly parked on a treadmill.
I'm still trying to envision a treadmill that applies as much force to an aircraft through friction at the wheel bearings as the engines do grabbing at the air.
Without setting fire to the wheelbearings.
Especially interesting in the case of a rocketplane like the Bell X-1, which not many people know was capable of a runway takeoff.
I wonder how fast the treadmill would have to go...:-)
... as it was mistakenly parked on a treadmill.
Nah, it was just left out in the weather for like forever.
i read the question....thought about it..decided that the rotation of the wheels nullified the movement of the treadmill..then i decided to wait to see what Happy Monkey would say, and knew i was right when he agreed.
Heh, thanks.
There is no "right" answer.
The right answer is the one that requires no magic treadmill. The plane takes off.
You are a good sport Sky.:)
;) :)
I think I'm getting a clearer picture of the car / plane confusion. The wheels on a car rotate, grab the road (with friction), and 'push the road back'. Since the road doesn't move, the car moves forward instead. So, you could change the speed of the car relative to the earth by moving the road like a treadmill.
With a plane, however, the the only purpose of the wheels is to keep the plane above the ground and reduce friction. The plane pushes itself forward by pushing the air back (hence it is easier to take off in a headwind).
Probably the only way to keep the plane from flying would be to immerse it in a tailwind that matched the plane's velocity, or to lash it down and prevent it from rolling.
I also think that people might be confusing velocity and force. Only force can keep the plane from moving, and the treadmill cannot apply enough force.
If you replace the word "force" with "Chuck Norris" you may be on to something.
rotating 200 mph, yes. moving 100 mph as the plane carries them
Oh, gotcha. :redface: Yes, of course.
That channel wing would be very difficult and expensive to build, although with composites it might be feasible. But, like Maggie said, heavy.
With a plane, however, the the only purpose of the wheels is to keep the plane above the ground and reduce friction. The plane pushes itself forward by pushing the air back.
Probably the only way to keep the plane from flying would be to immerse it in a tailwind that matched the plane's velocity,
As was
posted previously:
So that velocity of a plane is totally irrelevant to ground. Wheels will spin as slow or as fast as necessary so that velocity of the runway and velocity of plane stay totally independent.
Posting by Torrere is that airplane wheels make that plane 'separate from' (independent of) both runway and treadmill. Treadmill only affects how fast those wheels spin. As MaggieL
posted, otherwise those wheels would burn up; function instead like brakes.
Meanwhile, tailwind does not change the problem. Remember the two items that a force - the engine - applies between. Engine force pushes between airplane and air. Tailwind or headwind - still that engine applies same force causing the airplane to have a same velocity relative to air (also called airspeed). Still that same F=ma equation applies. No matter how fast the tailwind is blowing, F=ma makes the plane move a defined speed faster than air because same force (F) is remains between air and the airplane.
Airplane speed relative to runway is speed of airplane created by its engine plus speed of air created by tailwind.
Headwind/tailwind changes the airspeed by the velocity of the wind. A tailwind will make it harder for the plane to reach the airspeed necessary to lift off. And a headwind will make it easier. ;)
It only took us 18 pages, but lookout123 has solved the problem. The giant supernatural treadmill is irrelevant; only Chuck Norris prevent the airplane's movement. Since the problem did not specify that Chuck Norris was holding it back, the airplane flies.
Imagine the treadmill is powered by a jet engine. One thrust cancels out the other one. Nothing flys.
Imagine the treadmill is powered by a jet engine. One thrust cancels out the other one. Nothing flys.
wrong, and misspelled. (flies)
the runway could be powered by chuck norris and clint eastwood and labrat's ass put together. the rotation of the wheels nullifies it's effect. up up and away.
Treadmill only affects how fast those wheels spin. As MaggieL posted, otherwise those wheels would burn up; function instead like brakes.
I think they're in danger of burning anyway. Their friction is the only path for the treadmill to transfer energy to the airplane, and they've been specifically designed *not* to do that, whereas the engines are designed specifically to do exactly what they're doing. So the proposed takeoff failure scenario has a power transfer through friction in the wheel bearings equal to the power output of the engines (less engine system losses, of course). So even in a smallish airplane we're talking 100-200 horsepower...which is about 150 kilowatts. How long before the wheel bearings fail from heat?
I think they're in danger of burning anyway. Their friction is the only path for the treadmill to transfer energy to the airplane, and they've been specifically designed *not* to do that, whereas the engines are designed specifically to do exactly what they're doing. So the proposed takeoff failure scenario has a power transfer through friction in the wheel bearings equal to the power output of the engines (less engine system losses, of course). So even in a smallish airplane we're talking 100-200 horsepower...which is about 150 kilowatts. How long before the wheel bearings fail from heat?
My auto inspection shop complains about the cost of their treadmill. $20,000+ to test hundreds of horsepower cars (a machine required by the state required and that has not purpose only years later). Same treadmills exist for Indy and F1 racers designed to test 500 and 800 HP engines. I think we can find those bearings.
Maybe we and the Russians could cooperate on buiding one for airports? Anything for world peace. And since we are using labrat's ass, then it would be methane powered. Reduced global warming. No tailwinds. Having tapped chuck norris, the reduction in bullshit story lines means no additional landfills. Clearly there are plenty of spinoffs from this original proposal including 18 pages of deep technical discusion that would make any Congressman proud.
Same treadmills exist for Indy and F1 racers designed to test 500 and 800 HP engines. I think we can find those bearings.
Not quite the same thing. The dynamometers you speak of are purpose built to carry the load of a race car in normal operation. The "no-fly zone" treadmill must run fast enough to dissipate the equivalant of
all the power of the aircraft engine[s] through friction
at the landing gear bearings alone. (I grant you can postulate treadmills of any desired power handling capability; Heinlein certainly did--convincingly--in "The Roads Must Roll").
The bearings in question are the
landing gear wheel bearings, not anything in the treadmill. They weren't built to do anything more than handle relatively short takeoff and landing rolls near the stall speed of the aircraft, and some taxiing around at speeds about as fast as a man can walk.
I will probably be shunned for resurrecting this thread... but I had to bring to everyone's attention that this topic
will be covered on "Mythbusters" this week.
Found recently
Clearly in this case the plane will not take off . . . it won't get past the obstruction at the front of the treadmill.
I think this treadmill was designed for landings only, Sleeve.
They're thinking of installing one at Heathrow.
Help me Obi Wan!!! wow, my brain hurts.
I say no. If the plane is on a tread milbl, there is no forward motion....no Bernoulli effect.
Try this, same question different object...
An armored personnel carrier with full tracks, is driving down the road at 30 MPH. How fast is a track shoe touching the ground, centered on the vehicle moving and in what direction?
An armored personnel carrier with full tracks, is driving down the road at 30 MPH. How fast is a track shoe touching the ground, centered on the vehicle moving and in what direction?
Who the fuck cares -just run in the away direction. fast!
Help me Obi Wan!!! wow, my brain hurts.
I say no. If the plane is on a tread milbl, there is no forward motion....no Bernoulli effect.
Try this, same question different object...
An armored personnel carrier with full tracks, is driving down the road at 30 MPH. How fast is a track shoe touching the ground, centered on the vehicle moving and in what direction?
don't they wear combat boots anymore?
if you mean the little bits of the tank tracks.....i thought they stayed still?
so ....0mph?
Help me Obi Wan!!! wow, my brain hurts.
I say no. If the plane is on a tread milbl, there is no forward motion....no Bernoulli effect.
Try this, same question different object...
An armored personnel carrier with full tracks, is driving down the road at 30 MPH. How fast is a track shoe touching the ground, centered on the vehicle moving and in what direction?
There's no such thing as absolute velocity - all velocity is relative.
Relative to the ground, the part of the track touching the ground is not moving. The upper track is moving forward at twice the velocity of the vehicle (60 mph, in this case).
ohhh HLJ is a smarty pants!
You Sir, get a chocolate cigar!
Clearly in this case the plane will not take off . . . it won't get past the obstruction at the front of the treadmill.
My crush on SD grows stronger...
A plane is standing on a runway that can move, like a giant treadmill. When the plane's engines throttle up, it begins to move forward, but the treadmill is made to match the forward speed of the plane, only in the opposite direction. So, as the plane moves forward, it moves backwards beneath the aircraft.
As the engines throttle up, does the plane take off?
I will place my answer and explanation in the context of a few assumptions which follow:
1) We will assume that every piece of equipment will function as intended, regardless of the stresses placed on it. This means that the treadmill and the plane's landing gear will not simply fail by being misused.
We need to assume this because if we don't, the problem is subject to wild speculation on the capability of different elements of the model. One person may think the hypothetical treadmill is only capable of 35mph, another than the engines will overheat and explode if run at higher than taxi speeds without adequate airflow.
2) All other factors that are unstated are assumed not to exist, and will never become important to the conclusion. This means there is no headwind or tailwind, and the action of the treadmill will not create one.
Obviously adding elements not stated can alter the outcome enormously.
3) The airplane's engines are capable of finite thrust, equivalent to any real world example you choose.
4) The hypothetical treadmill is capable of infinite exertion within its role; it will move as quickly as required to keep the plane from moving forward.
We cannot simply say that the hypothetical treadmill is not capable of doing something the model specifically states it will do. That would change the original question itself. (BTW, the particular way the treadmill is stated in the problem is incorrect, but this interpretation attempts to follow the spirit of the question)
5) While equipment is assumed to function as intended, they are still subject to physical limitations. The landing gear are not perfectly frictionless, etc.
So, within this context, the plane can never take off. Lets first look at the plane at rest and the forces acting on it.
At rest, the plane is held in place by inertia and the friction of the landing gear. The landing gear is designed to reduce friction (compared to the belly of the plane), but it is not enough to simply glide across the runway with the slightest push. During use the landing gear will heat up due to this friction, with all the vibration and heat coming from the energy sapped by said friction.
Now if we start up the system the plane must be able to roll forward in order to create the lift required to take off. So, the question becomes "Can the airplane roll forward?" The plane pushes against the air and is held back by the friction of the landing gear, which will scale according to a small percentage of the speed of the wheels against the treadmill. Since the landing gear will always be able to provide a little more resistance if the treadmill's speed increases, the plane cannot roll forward and thus will never take off.
Practical issues with this model include the potential friction absorption capacity of the landing gear itself. The average jet engine can probably output enough thrust to exceed the capacity of the landing gear to shed energy, and they would fail spectacularly at some point. The treadmill will also end up traveling at astounding speed, and might end up creating significant airflow even supposing it could be constructed. But, that isn't the question we were asked.
We cannot simply say that the hypothetical treadmill is not capable of doing something the model specifically states it will do. That would change the original question itself. (BTW, the particular way the treadmill is stated in the problem is incorrect, but this interpretation attempts to follow the spirit of the question)
That's your mistake. The trick in the trick question is that it is phrased in a way that encourages you to interpret its spirit rather than its words. It subtly encourages you to choose the physically impossible interpretation.
If there are two interpretations, and one requires a treadmill that can stop a jet engine using friction in the bearings of the landing gear, pick the other interpretation.
If there are two interpretations, and one requires a treadmill that can stop a jet engine using friction in the bearings of the landing gear, pick the other interpretation.
One interpretation requires a treadmill to stop a jet engine using friction in the bearings of the landing gear, which is theoretically possible.
The other interpretation is not internally consistent as it requires the treadmill to be simultaneously stationary and moving. (If the plane rolls forward and the treadmill is matching speed as compared to the ground, to keep it stationary would imply that the treadmill is stationary as well, but also moving at twice the speed the plane is attempting to accelerate) I chose the one that made sense.
Thanks steve. I really appreciate the social responsibility you showed by re-opening this thread.
It subtly encourages you to choose the physically impossible interpretation.
Also, what is so physically impossible about stopping a jet with landing gear friction? I would wager that the friction of even a single 747's landing gear assembly can stop the thrust of my model rocket's engine, even without a treadmill. If you don't dispute that, the question becomes if the friction scales with speed, which should be clear.
Thanks steve. I really appreciate the social responsibility you showed by re-opening this thread.
Just think of it as my own little contribution to our community.
Shawnee seems to be the only one who has given this any serious thought.
The other interpretation is not internally consistent as it requires the treadmill to be simultaneously stationary and moving. (If the plane rolls forward and the treadmill is matching speed as compared to the ground, to keep it stationary would imply that the treadmill is stationary as well, but also moving at twice the speed the plane is attempting to accelerate) I chose the one that made sense.
Where are you getting the highlighted bit, from the question?
Plane moves forward, relative to the ground, at speed X.
Treadmill moves backward, relative to the ground, at matching speed X.
Wheels spin at 2 X as plane takes off.
The question tries to trick you into thinking that the "spirit" of the question is that the plane is held stationary relative to the ground, but the words of the question make no such claim.
Where are you getting the highlighted bit, from the question?
Plane moves forward, relative to the ground, at speed X.
Treadmill moves backward, relative to the ground, at matching speed X.
Wheels spin at 2 X as plane takes off.
The question tries to trick you into thinking that the "spirit" of the question is that the plane is held stationary relative to the ground, but the words of the question make no such claim.
Plane moves forward, relative to the ground, at speed X.(wheels spin at X, unless you are suggesting chunks of them are departing the plane)
Treadmill moves backward, relative to the ground, at matching speed X.
Wheels spin at 2X - so the treadmill must be moving at 2X.
Wheels spin at 4X - so the treadmill must be moving at 4X.
Wheels.....
And thus the problem with the statement. Obviously someone was trying to say something else.
Plane moves forward, relative to the ground, at speed X.(wheels spin at X, unless you are suggesting chunks of them are departing the plane)
Treadmill moves backward, relative to the ground, at matching speed X.
Wheels spin at 2X
Yes...
- so the treadmill must be moving at 2X.
No.
Or, more accurately, the treadmill is moving at 2X,
relative to the plane. It it still, however, only moving at X relative to the ground, matching the plane.
The treadmill matches the plane speed, both speeds relative to the ground. The plane moves at X, the treadmill moves at X in the other direction, and the wheels spin as if the plane were moving at 2X.
Plane moves forward, relative to the ground, at speed X.(wheels spin at X, unless you are suggesting chunks of them are departing the plane)
I disagree. The wheels don't spin at X. As soon as the plane begins to move forward, the treadmill instantaneously kicks into gear, and the wheels have to move 2X just to keep up with the plane. The plane moves X, but the wheels instantaneously move at 2X.
Treadmill moves backward, relative to the ground, at matching speed X.
Yes.
Wheels spin at 2X - so the treadmill must be moving at 2X.
I disagree again. The wheels move at 2X, but the treadmill moves at X. This is why the plane is moving forward relative to the ground.
Treadmills are activated by the force applied to their surface. There is no drive power coming from the wheels. No force
= no treadmill movement. The plane will lift off but won't clear the Universal Gym.
[COLOR="White"]Dirty Damn SteveDallas[/COLOR]
Yes...
No.
Or, more accurately, the treadmill is moving at 2X, relative to the plane. It it still, however, only moving at X relative to the ground, matching the plane.
The treadmill matches the plane speed, both speeds relative to the ground. The plane moves at X, the treadmill moves at X in the other direction, and the wheels spin as if the plane were moving at 2X.
But then it's a circular question. For those saying that the plane doesn't move, relative to the ground, X = 0 and 2X = 0, so the treadmill doesn't turn and the plane can't take off. But if the treadmill doesn't turn, the plane can move as normal and will take off as from a normal runway. Which proves that the plane will take off.
I'm so out of this thread once it passes the 200th post. mark my words.
DAMN IT!
Let's just read the question and decide what we're being asked about:
First, the plane "begins to move forward." So, forward motion is possible, although it isn't stated whether this forward motion is relative to the surface of the treadmill, or relative to the ground.
Next, the treadmill is described. It is "made to match the forward speed of the plane, only in the opposite direction." What the forward speed of the plane is relative to remains unspecified. The treadmill is said to "move backwards beneath the aircraft as the aircraft moves forward." What the forward motion of the plane is relative to remains unspecified.
Thus, when the treadmill is said to "match the forward speed" of the plane, it isn't stated how this speed is determined. When the treadmill is said to "move backwards...as the aircraft moves forward" it isn't stated how this motion is determined.
So, for step number one, to read the question and determine the parameters of what is being described, we cannot describe the treadmill because we cannot describe the plane, therefore we certainly cannot describe their relationship.
When Mythbusters tests this scenario, I will be curious to see what is tested. Because the question as stated here isn't something you can test.
For the record, the plane will not take off!
That is simply my opinion which is worth as much as you paid for it.
[COLOR="White"]but I'm still right :p [/COLOR]
The plane will take off.
As Newton said to Edmund Halley, "I have calculated it."
Next, the treadmill is described. It is "made to match the forward speed of the plane, only in the opposite direction." What the forward speed of the plane is relative to remains unspecified.
Right. That's what makes it a trick question. The first instinct of someone who knows how wings work is to assume that the spirit of the question is that the plane is held stationary. That assumption is not present in the question. Phage0070's wheel friction interpretation is the most grounded in reality of the ways to follow that line of thought, but even that requires the additional assumption of landing gear that can survive the friction (against the road, and internally on the bearings) required to counter an airplane engine, which would likely be several times the speed of sound.
The "relative to the ground" interpretation can actually be done with a real plane, so I'm guessing that that's the one the Mythbusters will do.
Oh for Christ's sake... IT'LL BE ON IN JUST A FEW HOURS.
Just sit tight and wait, 'kay?
my prediction is that the Mythbusters episode will do naught but inflame the argument into further heretofore unrealized levels of ridiculousness.
First, the plane "begins to move forward." So, forward motion is possible, although it isn't stated whether this forward motion is relative to the surface of the treadmill, or relative to the ground.
Go right back to Kitsume's post #1.
A plane is standing on a runway that can move, like a giant treadmill. When the plane's engines throttle up, it begins to move forward, ...
That means the plane moves forward relative to air - independent and irrelevant to a treadmill.
Between plane and the treadmill are wheels. Wheels spin as slow or fast as necessary so that plane and treadmill remain completely
independent of each other. Grasp the major significance of the word
independent. Tread mill moving forwards or backwards will only affect how fast and which direction wheels spin. Tread mill will have no affect on the plane.
I am still completely mystified why this is not obvious to everyone. In post
104, Happy Monkey again and accurately answered. He is answering to others who remain confuse in post
196.
Meanwhile, the question was answered in maybe five different ways - all coming to the same conclusion - in post
152.
First - what is the purpose of wheels (landing gear)? Velocity of a plane is totally irrelevant to ground. Wheels will spin as slow or as fast as necessary so that volocity of the runway and velocity of plane stay totally independent.
Does not matter what speed or direction (a one dimensional problem) a treadmill moves. It is that simple. Some still have difficulty after 305 posts and 13 months later? I am completely baffled why something so simple has been made so difficult.
It's this simple. Wheels mean the plane is not affected by the treadmill (except by some trivial bearing resistance that is made 100% irrelevant by the planes jet engines). Wheels and jet engine means the treadmill can be replaced by a runway (a treadmill moving as 0 Km/sec) and have the exact same answer.
And not a single comment about Bush, he must be drinking, he is slipping. :D
And not a single comment about Bush, he must be drinking, he is slipping. :D
Wheels on a jet plane even make the Bushes irrelevant to the problem. In 356 days, even we will be
independent of the bushes (which is really only a good place to pee).
I knew your obsession would never leave you. Who are you going to talk about when he is gone?
I ran on a treadmill for about 35 minutes the other day, I did not move forward. Does it matter if it's me or a jet plane on the tread mill?
I am totally tailposting here, but.......
Isn't the issue the planes speed relative to the earth? If the plane is spinning on a treadmill, then it isn't moving at all relative to the earth. I must be missing something - lil help?
No. No lift, as UT said. Planes do not take off from a stationary position. What would you expect it to do, suddently leap in the air? At what speed? From zero to what, in how many seconds? Same question: if you drop a paper airplane on the ground, will it suddenly leap in to the air and fly for no apparent reason? Same answer: No. The end.
No! The engines (normally) move the plane forward to make air go across the wings and produce lift. No going forward, no lift, no take off.
It's not already in the air, and it will never get there from a staionary position. The engines DO NOT "push" the plane into the air.
No. The movement of air over the wings does it. No movement = no lift = it will not take off.
Forget the wheels. The plane needs to move against the air to generate lift, to take off. It can't move against the air, so it can't take off.
:D
Yes it does, your forward movement is foot (wheel) driven and the plane's is not.
The wheels are irrelevant.
if there were no wheels, the plane would fall off the treadmill you dill.
yeah....the treadmill is unable to cancel the plane's motion because the wheels of the plane negate any and all reverse motion the treadmill can generate.
the wheels are what power the treadmill in reverse - therefore a net movement of.......................
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yup still ZERO.
cock
Plane wheels, freewheel. They have no effect on the movement of the plane unless you put the brakes on.
yes - de plane, de plane!
Plane wheels, freewheel. They have no effect on the movement of the plane unless you put the brakes on.
The impetus created by the forward thrust of the plane's engines is negated by an equal and opposite "thrust" of the treadmill. The plane is "treading water."
not if the wheels are free to spin, it isnt.
You know how cyclists can get those rollers that they can use indoors to train on when it's raining?
Well, this treadmill thing is the same concept really in some ways. If planes were able to take off simply by the thrust created by engines from the treadmill, doesn't it stand to reason that airports would create some kind of giant set of rollers so they don't need long runways?
:rollhappy :rollhappy :rollhappy :rollhappy :rollhappy :rollhappy
[size=1]You were almost right, LJ. The Mythbusters episode didn't cause people to argue more--only people who obviously didn't watch it to continue to rehash arguments from the last eight thousand pages...[/size]
Hey classicman: SHUT UP AND WATCH THE GODDAMN EPISODE.
Ali, I'll make a small concession for you since you perhaps can't get the show in Oz. Cyclists--just like cars, just like people's feet on a treadmill--are pushing on the ground to go forward. The plane is not pushing on the ground, with its wheels or anything else. It's pushing on the air with those massively explosive jets it has.
You know where else planes can take off from?
WATER. That shit's just as slippery as a backwards-moving treadmill.
Huh, didn't see the episode..So, the plane took off from the treadmill?
I'd say I hate it when I"m wrong, but it happens so often that I've become used to it.
Thanks...Goes back to running on treadmill, and roasting my noodle thinking about all of this.
Maybe this will help: just imagine what would happen if, while running in place on your treadmill, you strapped a jet pack to your back and turned it on.
Well why don't airports have big rollers then instead of making massive runways?
Because the jets would push the plane off the rollers before it had enough airspeed to take off.
Well I don't understand why that would happen if the bearings are loose enough or however you engineer those sorts of things. I guess that's why I'm not an engineer.
Well why don't airports have big rollers then instead of making massive runways?
Because the treadmill effect is irrelevant to the takeoff. The plane still needs just as much runway, whether it's a treadmill or not. All the rollers would do is make the massive runway more expensive, and prevent planes from using their brakes on it when landing or taxiing.
The treadmill does not stop the plane from moving forward.
If you were standing in a position such that you could see the plane, but not the runway, you wouldn't be able to tell from the plane's movement whether there was a treadmill. It still moves forward the same distance, relative to the air, before lifting off.
Hmmmm...I didn't think about landing.
Thanks for the explanation too HM. I understand now.
Well they never told you that it was a Harrier. So the wheels never move and the treadmill never moves.
Hey classicman: SHUT UP AND WATCH THE GODDAMN EPISODE.
Geez - ok. I was wrong! Lighten up Clod.
[SIZE="1"]I still don't get it though.[/SIZE]
Do you get how a water plane takes off, classic?
no I'm not a freakin pilot - I don't get the concept at all - I'm just too stupid I guess - kthxbye.
Back in the 80's, Letterman did a stunt in the hallway of NBC studios where he sat in a wheeled office chair and discharged a fire extinguisher. He was doing races down the hall with another guy. This problem reminded me a bit of that.
oh. so what you are saying is that the plane won't take off?
OK, reading all this makes my brain hurt.
What did Mythbusters say?
OK, reading all this makes my brain hurt.
What did Mythbusters say?
Yah. Me too. I was busy assembling my new treadmill from bigbox mart and missed the show. What fun. Not.
Yah. Me too. I was busy assembling my new treadmill from bigbox mart and missed the show. What fun. Not.
:lol: I bet the plane is going to be even harder to assemble.
When Mythbusters tests this scenario, I will be curious to see what is tested. Because the question as stated here isn't something you can test.
An airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff.
Busted. I love how they phrased the question so they could bust it. If the myth had been "the plane
can take off" it would have been confirmed.
[youtube]IbRcg3ji_Pc[/youtube]
The plane took off.
So, why is there still an argument?[/horrible tailposting]
Wtf? The plane was moving forward...so the treadmill wasn't equal to the plane? Well duh, it's not stationary as the original question seemed to suggest, of course it will take off, it will just take the wheels longer to get up to speed.
:bolt:
Wtf? The plane was moving forward...so the treadmill wasn't equal to the plane?
It was moving backward relative to the ground at the same speed the plane was moving forward relative to the ground.
Well duh, it's not stationary as the original question seemed to suggest,
That was the trick in the trick question- it seems to suggest that the plane will be stationary, but doesn't actually say so.
of course it will take off, it will just take the wheels longer to get up to speed.
No. The wheels actually move twice as fast.
After viewing that video, I am no longer willing to concede......
I think
Busted. I love how they phrased the question so they could bust it. If the myth had been "the plane can take off" it would have been confirmed.
Right. "Plane can't take off": Busted. "Plane can take off": Confirmed.
All a little anti-climactic if'n you ask me. All the wasted popcorn. ;)
Busted. I love how they phrased the question so they could bust it. If the myth had been "the plane can take off" it would have been confirmed.
Right. "Plane can't take off": Busted. "Plane can take off": Confirmed.
Right. This is usually a
question: "
Can a plane on a treadmill take off
?"
But since they are the myth
busters they phrased it so they could score a "bust."
Also (separate point here) they phrased the scenario to specify "ground speed."
They ran the treadmill at takeoff velocity (25 mph). I wonder what the result would have been if they ran the treadmill at the plane's maximum velocity.
They ran the treadmill at takeoff velocity (25 mph). I wonder what the result would have been if they ran the treadmill at the plane's maximum velocity.
If enough viewers complain about their testing methods, they will revisit the myth. Sometimes they're wrong. I'd say this one is still wide open!
[SIZE="3"][COLOR="White"]
HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA HA ha ha ha ha ha ha ha :::groan::: [/COLOR][/SIZE]
They ran the treadmill at takeoff velocity (25 mph). I wonder what the result would have been if they ran the treadmill at the plane's maximum velocity.
The same thing. For axle friction to noticeably slow the plane would require a treadmill moving at unimaginable speed. Now that I think of it, a treadmill moving fast enough to slow the plane might even cause enough of a wind-tunnel effect to counteract that friction.
The same thing.
Not quite exactly the same thing, they would need a longer strip of fabric. [/nitpick]
Heh, I was origianally going to put in a caveat about the treadmill material. Doing it the way they were (dragging cloth across concrete), a longer (heavier) strip, being pulled faster might require a stronger material.
But that seemed like overkill.
i thought they would have done this with a remote control plane and a fabricated actual treadmill.
I don't think they appreciate the obstinance that the 'no take off faction' is capable of.
kitsune, you should start a poll in this thread. Make it public so that we can discriminate against those 'no fly' fuckers. k? thx...bai...
i thought they would have done this with a remote control plane and a fabricated actual treadmill.
They did, earlier in the episode.
:::swallows another bitter pill:::
grumble - grumble - grumble
They did, earlier in the episode.
AH..i got home too late to catch it...and couldnt stay up late enough for the re run at 1 am.
Anybody see Mythbusters where they did the airplane on a treadmill thing with a model plane? It did *not* take off.
You see what you've done, Els? One harmless little white lie to stir some shit, and all of a sudden this thread is at the top again. I hope you're happy.
No, no...its true. Its on their
website.
[SIZE=2][COLOR=Black]Procedure/Experimental Design: Using Grant's model airplane & Jaime's treadmill, they do a small scale test to see if the concept is feasible. Setting the treadmill to 11.3 mph (the take off speed of the model plane), the model plane went forward, but could not take off [COLOR=Red]due to the short length of the treadmill.[/COLOR] Next, using butchered paper dragged behind Adam's scooter, they put the plane on the paper to see if it can take off. The airplane does take off before the paper runs out. As Adam & Jaime explain, unlike a car, where forward motion is derived from spinning wheels, forward motion on an airplane is derived independent of the wheels through the propeller. Thus, forward motion can be achieved on a conveyor belt.
[/COLOR][/SIZE]
Damn it. I just watched the video. You didn't expect me to *read*, did you?
using butchered paper dragged behind Adam's scooter
Why they gotta beat up a perfectly nice piece of paper? Methinks they mean butcher paper?
Is this like "battered fish"?
I still agree with you Els - even though the damn thing took off - It still shouldn't have.
NO
It wont take off, the planes wings need air rushing through them to genarate lift. unless it can flap
:P
The air moving over the wings is created by the props pushing it or jets pushing the plane through it. The wheels only eliminate the friction between the plane and the ground, and are irrelevant.
Up it goes.
Holy crap - Here we go again! ::giggle:
We need Samuel Jackson to drop by and declare...
"I have had it with these motherfucking planes on this motherfucking treadmill!"
Don't worry, the Northwest treadmiills are on strike again....
Never mind will it take off?
Will It Put Out?
And would you risk a BJ? :eek:
:lol:
Ooh, a hovering BJ!
The first step towards zero G sex.
Well that's just great. We resolved "The 'Plane on a Treadmill' Question"; but, now we have to resolve "The 'Helicopter on an Escalator' Question". :headshake
Many great minds of science have ruminated on this vital issue. They were less concerned with how close, though, than with how period, since landing upside down is no mean feat.
The leading theory for years was that the flies did a half barrel roll sideways a la the Blue Angels just before landing. This idea was shot down in 1958 when Natural History magazine published photos showing that in fact flies do a sort of backward somersault.
On approaching the ceiling, and while still flying right side up, flies extend their forelegs over their heads till they can grab a landing spot with the suction cups in their feet. Their momentum then enables them to swing their hind legs up, like a gymnast on a trapeze. Result: inverted fly, home and dry. So the answer to your query is, they get real close.
Good lord, is this still going on? The plane takes off. I said so. /thread
We need Samuel Jackson to drop by and declare...
"I have had it with these motherfucking planes on this motherfucking treadmill!"
you couldn't wait 10 days to post that?
also, it would go backwards
No, the wheel isn't driven by the belt, it's driven by the small roller/motor in front of the wheel.
oh..i didnt notice that.
so, that wheel reverses the direction.....
The caption I saw with the picture said the wheel was driven separately from the belt. It didn't explain if it was a separate motor or some kind of linkages.
shit. now what.
that is gonna be one tired bird.
One retarded pigeon, doesn't not conclusive make. :headshake
One retarded pigeon, doesn't not conclusive make. :headshake
What about this Shrimp on a treadmill?
I forget where it came from and what the researchers were attempting to discern.
[YOUTUBE]cMO8Pyi3UpY[/YOUTUBE]
Or where they found such a stupid shrimp. :unsure:
i'm too hungover for this.
i'll think about it tomorrow when i go fly with Bobby.
i'm too hungover for this.
i'll think about it tomorrow when i go fly with Bobby.
Will you be taking off from a treadmill?
Okay, in regards to the eternal question of "can it take off from a treadmilll?" the tally so far is planes, yes, pigeons and shrimp, no.
What about
coked-up reindeer?
To compare nasal blood flow across species, the research team recruited five human test subjects from the Academic Medical Center at the University of Amsterdam, where some of the authors are based, and shoved a video microscope up their noses to chart blood flow. Furthermore, the researchers tested vascular reactivity (i.e. how much the blood vessels can change) by "local application" of 100 mg of cocaine, a common vasoconstrictor used in ear, nose, and throat research, to the interior of one of the subject's noses.
The team then anesthetized a pair of adult reindeer and did a similar microscope survey of blood vessels, then put the reindeer on treadmills to heat them up, and recorded where their heat output was highest with a thermal imager:
There is no record of the reindeer achieving lift-off.
I guess they need more cocaine.
Will you be taking off from a treadmill?
we should have tried. that was a fucked up flight.
[YOUTUBE]7osw2jcsi6Q[/YOUTUBE]