. Why is friction called a necessary evil? 11. Why
12. (a) What is a lubricant?
(b) How does a lubricant reduce friction?
(c) What kind of lubricant is used in
() a sewing machine, (ii) the axle of a tractor?
Answers
Answer:
A) Friction is called necessary evil because it causes wear and tear of various moving parts.
B) Lubricant makes the surface smooth which reduces the contact surface area of various parts.
Answer:
11.Friction is necessity
(1) It is due to friction between the ground and the feet that we are able to walk.
(2) The brakes of a vehicle cannot work without friction.
(3) Various parts of a machine are able to rotate because of friction between belt and pulley.
(4) The tyres of vehicles are made rough to increase friction.
(5) Nails and screws join various wooden parts due to friction.
(6) In the absence of friction it will not be possible to write on paper with a pen or pencil.
Friction is an evil:
(1) Wear and tear of machinery is due to friction.
(2) A large amount of power is wasted in overcoming friction and the efficiency of the machines decrease considerably.
(3) Excessive friction between rotating parts of a machine producers enough heat and causes damage to the machinery.
As friction has both advantages and disadvantages, we can say that friction is a necessary evil.
12. (a) A lubricant is a substance, usually organic, introduced to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, transporting foreign particles, or heating or cooling the surfaces.
(b) Lubrication helps fill in the uneven zig zag surface, tries to make it smoother in order to allow smooth relative motion between the surfaces, thereby reducing friction.
(c) In the axle of a tractor grease oil is used frequently for the lubrication of the tractor parts. And for the smooth running of the axle of the tractor grease is used as a lubricant