The "Plane on a Treadmill" Question

[Flint]

Originally Posted by Undertoad

The plane will move forward but not enough to gain enough lift.

Originally Posted by glatt

Of course there is lift. The plane will move forward against the air, and twice as fast against the runway.

No, read the question:

Originally Posted by Kitsune

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.

[glatt]

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.

[Flint]

Originally Posted by glatt

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" . . .

Originally Posted by glatt

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.

[glatt]

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.

[glatt]

Originally Posted by Flint

There is no forward motion according to the question.

The question doesn't say that.