Quote Originally Posted by Chip View Post
Ang assumption ko dito is since the treadmill matches the wheel speed, the airplane never moves.
No. The plane will move because there is no friction between the plane and the treadmill, thanks to wheel bearings.

Now for example we put on a rocket pack (ala Wiley Coyote) on our backs and use it to propel us 5mph(on roller blades) on a treadmill running at exactly 5mph. Will there be movement? Still no.
Yes there will be movement because the roller blades effectively rendered the treadmill to be frictionless.

For example. You are on roller blades, standing on a very long treadmill. With treadmill not running, somebody pushes you forward momentarily and off you go rolling at constant speed. You will remain at the same speed forever if not stopped by very little friction force on the roller's bearings. Now while you are cruising at the same speed, the treadmill was started and moved backwards. Will you be slowing down now? No, because there is practically no friction between you and the treadmill surface. You simply continue to cruise at the same speed, but now the wheels are turning faster (because there is friction between the treadmill and the roller rubbers).

It doesnt matter where the source of propulsion is (this case rocket pack), since the treadmill will always match our forward velocity, there can be no speed.
It does matter where the propulsion is applied to a wheel. For a plane, propulsion is applied at the center of the wheel, similar to the roller blades, and wheel bearings effectively cancels out friction at the rubber surface. In this case, the plane (or the roller skater with jetpack) will move as usual, regardless of runway (or treadmill) movement.

For a car, propulsion is derived from friction between tire and road,i.e., propulsion is apllied at the bottom surface of the wheel. In this case, the basic intuition works. The car will remain stationary if the road matches the car speed. The car can be made to go forward or backwards depending on the difference of speed between wheel and road.

Kaya nga aircraft carriers and airports have certain runway lengths, that length is the minimum distance needed by the plane to acheive sufficient velocity to produce lift. Since running on the treadmill does not produce any velocity, no lift.

Ayoko nang pag-isipan to mamaya
With or without runway movement, the plane will move and take-off as usual requiring the same length of runway as usual.