Will the Airplane Fly??????????

[Alpha_One]

However, you could possibly mean torque when you say Ff on the car, as you seem to equate Ff with Fb. This is fine with me. I would just make it clear that torque T is quite different from a linear force such as Ff. I'd repeat myself ... for an isolated body, torque T will make the object rotate but it won't move the object, while a force such as Ff acting thru the center (of gravity, such as the center of a wheel) of the object will not rotate the object but it will move the object to the direction of the force. If a force Ff acts off-center on a body, it will cause the body to rotate only enough to align the center-of-gravity with the force and as soon as alignment is completed, rotation stops but object will continue to move.

Torque, that's the correct word, thank you! No, I don't mean Ff=Fb, just that whatever force the car pushes the car backward the engine can overcome by generating enough torque at the wheels. Once it generates enough torque at the wheels to be able to convert enough forward linear force to overcome all the backwards linear forces, it's not necessary that the conveyor will be pushed back, because it will match the *car* speed not the *wheel* speed.

The elevator race example is simple. It seeks to demonstrate that you *can* move across a moving platform that's moving in the opposite direction as you are, whatever it is that's propelling you. The platform, even if it's going backwards, still has a enough backwards resistance that allows you to push against it in order to move forward. The elevator isn't slipping back farther if you use enough force on your feet to get a net forward movement across an elevator moving backwards.