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Jan24-10, 07:02 AM
P: 45

Jet when fly not have friction with ground, but it has wings, so wings frictring to air.
Bicycle driven with propeller not have wing, who fricting to air, but have wheels, who fricting to ground and ball-bearings (and not front wheel bicycle have free-wheel, what about 3 times make biger friction, about 3-4 times faster stop back wheel, than front wheel, when you rotate its with same speed).

I think, that showen in image is not correct (how you think?), because then possible be ride with about 20 W motor on 8 km/h speed.

Must be like this, I think: