Monday, September 8, 2008

Can Tony Hawk Take Off From A Treadmill?

The alt-text for today's xkcd comic refers to a traditional internet flamewar of which I had not been aware: whether an airplane can take off from a treadmill.

After looking into it, it seems like one of the most convincing intuitive arguments supporting the correct answer involves pulling oneself forward over a treadmill while on a skateboard or while wearing roller skates. I seem to remember that the airport level in Tony Hawk 3 featured some moving walkways, but I can't remember whether they affect your ground speed when you roll over them.

(Obviously, the physics in Tony Hawk demonstrate rigorous adherence to reality in all other regards.)


DU said...

Mythbusters covered this, but poorly IMO. They were insufficiently clear about what's going on.

It's an ill-defined problem. Or maybe it's that what seems to be a logic/physics problem is really an airplane design one.

If the engine drives the wheels, it can't take off. If the wheels are free spinning, it can. Is the normal human being, even if well-versed in physics, going to know exactly how airplanes are built? There's no logical reason they couldn't be made both ways.

DU said...

Also, Straight Dope beat you to the punch (nullus) by 2.5 years:

tps12 said...

I thought of the "if the engine drives the wheels" thing as well, but then I realized that that would be a really silly way to design an airplane. (I.e., there is a logical reason not to do it that way.)

But yeah, wasn't trying to break this particular story, since I'm obviously late to the party. Just thought it was funny that one of the major examples used to argue it shows up in a video game. (And FWIW, to the best of my recollection the game gets it right; though I think I remember feeling like it was wrong.)

DU said...

Just realized that some birds effectively do this the "wrong" way. That is, their "engines" drive their "wheels" but they can still take off on a treadmill (i.e. by running across the surface of a lake).

I had a long thing about rockets and inertia here, but all I've managed to prove is that treadmills can't exist.