Let's consider a wheel rotating
Now, when wheel rotates, the hub (central hole) rubs against the rotating axle
This causes sliding friction
To prevent that, we use ball bearings in the hub of the wheel.
When ball bearings are used, the bearings roll between the hub and axle
Since rolling friction is less than sliding friction. Ball bearings decreases friction
Example
Ball Bearings are used between hubs and axles of Ceiling fans and Bicycles
