What If? with Randall Munroe

http://what-if.xkcd.com

xkcd's Randall Munroe answers hypothetical questions with physics!

In Armageddon, a NASA guy comments that a plan to shoot a laser at the asteroid is like “shooting a b.b. gun at a freight train.” What would it take to stop an out-of-control freight train using only b.b. guns?
—Charles James O'Keefe

If cows could photosynthesize, how much less food would they need?
—Anonymous

What if you exploded a nuclear bomb (say, the Tsar Bomba) at the bottom of the Marianas Trench?
—Evin Sellin

What if a rainstorm dropped all of its water in a single giant drop?
—Michael Mcneill

Can i just reiterate how in love I am with him?

Whoa.

But regardless of which units you use, there’s something strange going on here. Miles are units of length, and gallons are volume—which is length^3. So gallons/mile is length^3/length. That’s just length^2.

Gas mileage is measured in square meters.

You can even plug it into Wolfram|Alpha, and it’ll tell you that 20 MPG is about 0.1 square millimeters (roughly the area of two pixels on a computer screen).

Unit cancellation is weird.