Christophe wrote:Ahmed if your crazy wheel theory was right you should be able to push a plane or a train just by touching it ... right? We must not have the same conception of the marginal ...
This is not "his" theory, it is Newton's first law! No force / energy is necessary to maintain a movement at constant speed, unless there are losses (friction, air resistance ...).
It takes an energy only to make it change speed, so if it was at rest either v = 0, to make it acquire a speed v> 0 (E = 1 / 2.m.v²), but this energy can be arbitrarily low if the final speed is arbitrarily low. So yes, touching an airplane or a train would set them in motion, as long as the friction had been eliminated, for example by sustaining them by a magnetic field rather than wheels or by assuming them to be weightless.
If your reasoning was correct then no freewheel could transmit power through a treadmill
It's the case. A wheelchair on a treadmill would stay put, if it were ideal (frictionless wheels). In practice, of course, there is always friction, the chair will be driven.
Newton's first law: no force (therefore no energy) is necessary to maintain uniform motion. An object at zero or constant speed remains like this as long as no force is exerted. In the cases we have seen, the force can only come from friction.
Are you really an engineer?