Why Does Oiling the Axle Make the Wheel Turn More Easily?
If you look at what appears to be a perfectly smooth axle on a bicycle or motor car through a powerful magnifying glass, you will find that the surface of the axle is not smooth at all, as you may have thought, but covered with what appear to be quite large bumps or irregularities in the surface. If you were to examine the inside of the hub of the wheel in the same way, you would find that it also is like that. Now, when you attempt to turn a wheel on the axle without oil, these little irregularities or bumps grind against each other, producing what we call friction. As friction develops heat, the metal of the axle and the hub expand and the wheel gets stuck.