wow…this question is being bickerd about on alot of threads… neat anyway…
ok…here is one that i pulled from a physics forum…and this guy sums it up pretty much as I believe…(and is true) here is what he said
"Plane takes off, as it does in the “original problem”. Engines apply force in direction d, wheels provide rolling resistance in direction -d. Since airplanes have engines designed to overcome all resisting forces likely to be encountered, plane moves forward, as is expected by conservation of momentum (thrust directed backwards, equal and opposite force forwards.
The conveyor belt is merely an unneeded contrivance to trick the gullible; this is a simple force balances problem with engine forces in one direction and resisting forces in another. Planes are designed to overcome resisting forces (wheels, drag, etc.) so off we go. For those who think otherwise, consider that the plane doesn’t “know” it has wheels, it just feels resisting forces on its wheel struts that are further transmitted to the body. The fact those resisting forces are generated by “rolling friction” doesn’t change the fact they are still simple adverse forces, like having the brakes on or having an uphill runway. The rolling conveyor is just a method of inducing added rolling friction force, it does not impart any rearward motion to the plane as the vector addition of the engine force and the resisting forces balance in favor of the engine.
Again, the key is that engine forces overwhelm adverse force by orders of magnitude in real aircraft. For those who think the conveyor moves the plane backwards, consider a plane confronting an uphill runway. When brakes are released the plane rolls back slightly then engines take charge and plane moves forward. The “thought experiment” of the conveyor somehow implies, equivalently, that the “uphill” runway dynamically get “steeper” as the plane attempts to make progress against it (implication: increasing adverse force). But airplanes, as we understand them, do not meet increasing adverse forces the engines can’t overcome (except for aero drag). That is, rolling resistance is negligible.
To pound the point home further, for those who somehow think the plane is “attached” to the conveyor and is moved backwards diabolically just as the plane tries to move forward: the plane’s engines do work W = F ds. For the conveyor to move the plane backwards the conveyor has to do the exact reverse. The only “F” the conveyor has to work with is the rolling resistance and shear inertia. Not enough, as demonstrated by planes taking off from non-conveyor runways. For those who think situation is same as runner on a treadmill: not the same. Runner/treadmill is a “closed system” while airplane engines working against air is an “open sysem”.
Note to Atl5p: you can attempt to reformulate this problem all you like, but until you constrain the plane to act in non-normal plane-like ways, you’re stuck: the plane flys. Forget the dumb conveyor and just do a little vector algebra to see why. "