How do ball- bearings affect the nature of friction? Illustrate with an example.

The ball- bearings reduce friction by converting sliding friction into rolling friction. For example, when the axle of a machine fitted with ball-bearings rotate, then the metal balls also roll and hence the friction is reduced. The free-wheels of bicycles, the axles of cars, the shaft of motors and many other machines are provided with ball-bearings to reduce friction.