Worksheet solutions for chapter: Friction for class 8 are provided below.
(1) A player hit a ball in the play ground. The ball stops its own. Explain.
Ans-The frictional force between the ball and the playground reduces and not able to overcome the interlocking between the ball and the playground. Therefore, the ball stops its own.
(2) What is rolling friction?
Ans-The force which is required to roll an object over the surface is known as rolling friction. Rolling reduces friction.
Eg:- (i) Rolling luggage over wheels is easy because it reduces friction.
(ii) Ball rolls over the ground and stops due to rolling friction.
(3) How teachers write on the black board with chalk?
Ans-The frictional force applied by the teachers to overcome the interlocking of chalk and surface of black board. Due to frictional force, the rough surface of the board rubs off some chalk particles which stick to the black board.
(4)What are lubricants? Give examples.
Ans-The substances which reduce friction are called lubricants.
Eg :- Oil, grease etc.
(5) Which type of foot wear will be good for the old people to save them from slipping?
Ans- The foot wear which has grooved sole are the best for the old people because they are not slippery. The grooves of the soles (rough surface) interlock with the floor and old people have to overcome interlocking by applying frictional force. Therefore, grooved sole does not slip and good for the old people.
(6) Why wheel is said to be one of the greatest inventions of mankind?
Ans- The force which we apply to roll one surface over other surface is the lowest. Therefore, it is very convenient to roll heavy weight on other surface. Wheels and other surface do not get time to come in contact or interlocking. Therefore, we need very less force of friction. Therefore, wheel makes our life easy. Hence, wheel is said to be one of the greatest inventions of mankind.
(7)Fill in the blanks.
(i) The frictional force exerted by fluid is also called ____.
(ii) Ball bearing in wheels _____ friction.
(iii) Friction produces ____.
(i) The frictional force exerted by fluid is also called drag.
(ii) Ball bearing in wheels reduces friction.
(iii) Friction produces heat.
(8) Explain, why jar of a mixer becomes hot when it is run for a few minutes.
Ans-Jar of a mixer becomes hot when it is run for a few minutes because of frictional force between jar and the mixer. This frictional force produces heat and jar becomes hot.
(9) Can we reduce friction to zero by polishing surfaces or using large amount of lubricants?
Ans- No, we can not reduce friction to zero by polishing surfaces or using large amount of lubricants. There is not any surface which is perfectly smooth. Every surface has some irregularities.
(10) Imagine that friction suddenly vanishes. How life would be affected. List five such situations.
If friction vanishes suddenly, the life would be affected adversely.
(i) We can not move or walk on the floor.
(ii) The birds can not fly.
(iii) We can not fix a nail.
(iv) There will be no use of ball bearings in the vehicles.
(v) The fish can not swim.
(vi) No vehicle will move on the roads.