Mention the methods use to decrease friction ?

1.Polishing : If surfaces are polished irregularities of the surfaces are removed and there by friction decreases.
2. Ball – Bearing : The hard steel balls (Called bearings) placed between the moving parts converts sliding friction into rolling friction hence friction is reduced.
3.Lubricants : Lubricants like oil (or) grease which spreads over the surface fills the irregularities of the surface there by the friction is reduced.
4.Stream lining : Automobiles and aeroplanes are streamlined to reduce the friction due to air.