when your on a tread mill your not using your arms to move are you

this is like asking if sea planes really take off form water ffs

If the plane is on a runaway that is moving in the opposite direction at the exact same speed as the plane then the relative travel of the plane to the air will be zero; the plane will be motionless (think running on a treadmill) and there will be no airflow across the wings to generate lift from.

Imagine a plane on ice with its wheels locked up - it can still take off - the speed at which the wheels turn around is irrelevant.

thinking running on a treadmill is the trap people fall into - if the plane was a car with wings then youd be right - however planes move by using a propeller or jet engine not by powering their wheels.

Supposing the plane produces enough thrust to move it forwards at 200mph - the theoretical runway therefore moves backwards at 200mph - all that is going to happen is the plane wheels will spin around at 400mph. The plane will still move forwards regardless as it isnt driven by its wheels it is driven by its jet engines.

I see what youre getting at; the plane is free wheeling, the thrust/drive is not dependant upon the friction/force of the wheels and ground.

If this is true why do planes need a runaway at all ? Why dont they all take off from a static start ?

the need runways for a smooth flat surface to get up to speed on and a long run to slow down on when landing as they deffo need the friction then

reverse thrust indeed but even so they need a surface to apply brakes on as well, and a Cessna wont be using reverse thrust anytime soon

is that not the truth?

wouldnt make a blind bit of difference.

As in order to get airflow over the wings, the plane needs to move.

If the road underneath is moving at speed that the plane will be doing over the ground, then there will be no net airflow over the wings. the plane will be stationary.

Put a rocket car on a treadmill... just because the force is applied elsewhere doesnt mean that it has no effect.

Push a car... now push a car on a treadmill that is so well lubricated theres next to no resistance, as the wheels roll, the road will move backwards. Keeping the car where it is.

You can push that car as hard as you like so long as the rollers match your speed perfectly and it aint going anywhere.

A plane... moving along the ground still has to overcome the resistance of its undercarriage on a road. if the road is giving way underneath it (moving backwards as it attempts to move forward) then it wont move.

Put a rocket on wheels horizontally and then put on the conveyor belt. The rocket is gonna move forward. The engine pushes against the air. The wheels add hardly any friction so it might as well be flying through the air.

Rollers wouldnt work cos the plane would move forwards and come off them.

A force diagram would explain all.

edit: Its been a long time since I did one of these, hope the arrows are pointing the right way;