Interesting problem over at Kottke.org with a massive amount of comments discussing it and arguing the case for each side.
Here’s the original problem essentially as it was posed to us: “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?”
Like Jason I initially thought that of course the plane couldn’t take off but then by rereading the problem I understood what is actually happening and realised that the plane would of course take off.
It’s almost a trick question as it seems to imply that the airplane is caused to remain stationary in respect to the ground and the air by the conveyor belt. If that were the case then it could never take off as it is the negative air pressure above the wing generated by the forward motion through the air that causes the lift.
But in fact the airplane would move forward as the conveyor belt only acts to move the wheels of the plane which are only connected to the plane by an axle which allows them to spin freely. They are nearly frictionless and so only a negligible amount of backward motion is actually transmitted to the plane. So no matter how fast the conveyor belt moves only a fraction of that motion is transmitted to the plane and so there is a net forward motion and as the plane moves forward it will pass through the air and gain lift as usual.
Tags: science
