Why are ball bearings used in machinery ?

The ball bearings used in a machine are of different materials, this is because

The ball bearings used in a machine are of different materials, this is because

Why is a ball bearing used in a cycle hub?

What is the purpose of using ball bearings in machines ?

Why do we use ball-bearings?

Define force of friction. How does the use of ball bearing reduce friction ?

The radius of a ball bearing measured by a screw gauge is 3.75mm . The pitch of the screw is 1mm and it has 100 divisions on its head scale. The percentage error in the volume of the ball bearing which is perfectly spherical by shape is