16. (a) Friction is desirable in some situations and undesirable in some other situations.
(i) Mention two applications where friction is increased by making the surface rough.
(ii) Also mention the name of any two methods which is used to reduce friction whenever it
becomes undesirable.
Answers
Answer:
a. Friction helps us to walk on the road easily without slipping . In this case friction is desirable.
Frictionction causes wear and tear and excess heat in machine parts. So here it is undesirable.
b. Black boards in classrooms are made rougher using various kinds of sand to enable teachers to write comfortably.
roads are often laid with a a layer of stone chip to increase friction between the road and the car tyres and to enable the car to run properly in case of rainy days.
c. Machine parts lubricated with grease and oil to prevent heating by reducing friction.
Skating – A thin film of water under the blade is necessary to make the skate slide. The heat generated by the skate blade rubbing against the surface of ice causes some of the ice to melt right below the blade where the skater glides over the ice. This water acts as a lubricant reducing friction.
Answer:
(a)Using lubricant
(b)ball bearing