The motion and power transmitted by gear is kinematically equivalent to that transmitted by friction wheel.
Consider two circular wheels A & B mounted on two parallel shafts and the wheels are pressed against each other. Shafts are mounted on anti-friction bearings.
When wheel A is rotated by shaft, it will rotate wheel B in opposite direction.
Force on the system:-
1.RN= Normal reaction between two rubbing wheels
2.T= Tangential force
3.F= Frictional Force (F= µRN),
where µ= co-efficient of friction
When T≤ µRN wheel B will rotated by wheel A
When T> µRN slippage will take place