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

[james]

Ok how about a different approach:

Imagine you could remove the wheels and replace them with anti-gravity devices so the plan just hovered a foot above the conveyer - would it be able to take of then? Of course - the engines provide thrust which gives the plane forward motion which moves air over the wings which provide lift. The action of the conveyor would have no effect on the planes ability to take off.

Assuming that the planes wheel brakes are off (as is normal for takeoff) they will only have a negligible effect on any motion of the plane with relation to whatever it is sitting on (a normal runway or a conveyor) so again the conveyors action will have no real bearing on the planes ability to take off. All that will happen by ramping up the conveyor speed to match the planes momentum is that the wheels will spin at twice the speed they would if it was taking off from an unmoving surface.

[jamie]

Ok how about a different approach:

Imagine you could remove the wheels and replace them with anti-gravity devices so the plan just hovered a foot above the conveyer - would it be able to take of then? Of course - the engines provide thrust which gives the plane forward motion which moves air over the wings which provide lift. The action of the conveyor would have no effect on the planes ability to take off.

Assuming that the planes wheel brakes are off (as is normal for takeoff) they will only have a negligible effect on any motion of the plane with relation to whatever it is sitting on (a normal runway or a conveyor) so again the conveyors action will have no real bearing on the planes ability to take off. All that will happen by ramping up the conveyor speed to match the planes momentum is that the wheels will spin at twice the speed they would if it was taking off from an unmoving surface.

WHAT?!! Anti gravity device!! In your example the plane has already taken off before yourve turned the engines on! There would be nothing stopping the forward or upward motion of the plane ie gravity...