Brainteaser Options

[james]

Here's a question for you:

"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?"

A couple of links discussing it (and some funny rationalizations for peoples incorrect assumptions):
www.kottke.org/06/02/plane-conveyor-belt
www.straightdope.com/columns/060203.html

[camsmith]

OK... My very first thought was no, but then I thought about it and changed my mind after about 30 secs.

For a plane to move, the thrust provided (regardless of propeller or jet) comes from the surrounding air, not from traction on the ground.

Therefore, the plane moves (accelerates) relative to the air, not the ground. Therefore, regardless of the speed of the ground, the plane will start to move. The wheels on the plane will simply spin twice as fast as the plane moves to compensate for the moving ground.

The only assumptions made are that the runway is a normal length runway for the plane, and that the friction generated by the wheels spinning twice as fast as normal is negligible.