Mention any two methods of reducing friction .

Explanation

Disadvantages of friction.
`(a)` Friction causes wear and tear of machinery parts.
`(b)` Friction slows down motion of bodies.
`(c )` Friction reduces the efficiency of machines
`(d)` Friction causes envirnomental pollution due to insufficient burning of fuels, wearing of the surfaces , noisy moving parts of the machinery.
Methods of reducing friction
`(a)` Lubricating machinery parts with oil, grease etc reduces friction.
`(b)` Polishing and powdering the same reduces force of friction on dancing floors, billiard and snooker boards etc.
`(c )` Aerodynamic shape of bodies produce less air friction in vehicle and less water friction in aquatic animals.
`(d)` Ball bearings and roller bearings reduce rolling friction.