Question

how does oiling and using ball bearings help reduce friction

Answer 1

Bearing reduce the friction of certain moving parts by replacing sliding friction. they are used to provide better linear motion or rotation around a fixed axis roller bearings are typically cylinders similar to free rollers ,while ball bearings are spheres that are held in a track

Answer 2

Instead of the jagged edges coming in contact, the lubricant acts as a smooth divider between the surfaces. This reduces friction and also heat generated. Ball bearings on the other hand reduce friction by changing the type of friction in effect. In the first image, sliding friction, or kinetic friction, was in effect.