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.
 

Yes, damnit! :)

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 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.

Sure they do. What, you think the wheels do it?