question_answer

Explain: (a) Why are ball bearings used in machinery? (b) Why does a horse have to apply more force to start a cart than to keep it moving? (c) What is the need for banking the tracks?                                          

Answer:

                (a) By using ball bearings between the moving parts of a machinery, the sliding friction gets converted into rolling friction. The rolling friction is much smaller than sliding friction. This reduces power dissipation. (b) During the first few steps of his motion, the horse has to work against the limiting friction and once the cart starts moving, the horse has to work against kinetic friction which is less than limiting friction. (c) When the circular track is banked, the horizontal component of the normal reaction of the road provides the necessary centripetal force for the vehicle to move it along the curved path. This reduces wear and tear of the tyres.