NCERT Solutions for Class 8th Science Chapter 14 Friction textual questions and answers based on the latest syllabus of CBSE and JKBOSE
1. Answer the following questions:
1.1 Why are the worn-out tyres discarded?
Worn-out tyres are discarded because their treads are eroded, reducing friction and increasing the risk of slipping.
1.2 Why do carom coins move faster on carom board when dusted with talcum powder?
Carom coins move faster on a carom board dusted with talcum powder because the powder reduces friction between the board and the coins.
1.3 Why is the surface of the conveyor belt made rough?
The surface of the conveyor belt is made rough to increase friction, which helps in the movement of objects placed on it without slipping.
1.4 Why is the sewing machine often oiled?
The sewing machine is often oiled to reduce friction between its moving parts, ensuring smooth operation.
1.5 Why do new automobile tyres have deep grooves?
New automobile tyres have deep grooves to increase friction with the road surface, providing better grip and control.
1.6 Why does a ball rolling on the ground slow down?
A ball rolling on the ground slows down due to friction between the ball and the ground.
1.7 Why are the boats and aeroplanes given special shape?
Boats and aeroplanes are given special shapes to reduce fluid friction and move smoothly through water and air, respectively.
1.8 Why do meteors burn on entering into the atmosphere?
Meteors burn on entering the atmosphere because of the friction between the meteor and the atmospheric gases, which generates heat.
1.9 Why do painters use sandpapers in polishing doors?
Painters use sandpapers in polishing doors to increase friction, which helps in smoothing the surface by removing rough spots.
1.10 Why is it easier to tie a knot with cotton string as compared to silk string?
It is easier to tie a knot with a cotton string as compared to a silk string because cotton has more friction, preventing the knot from slipping.
2. Fill in the blank spaces by choosing words from the list given below:
List: movement, sliding, streamlined, static, opposite
2.1 Friction always acts in the direction opposite to the direction of applied force.
2.2 Static friction is a self-adjusting force.
2.3 Friction is very useful as it helps in the movement of the bodies.
2.4 The sliding friction is 10 times the rolling friction.
2.5 The boats and aeroplanes are streamlined so as to reduce fluid friction.
3. Statements given below are incorrect. Write the correct statements.
3.1 Sliding friction is slightly more than the limiting friction.
Correct Statement: Sliding friction is less than the limiting friction.
3.2 The conveyor belts are made rough, in order to decrease friction.
Correct Statement: The conveyor belts are made rough, in order to increase friction.
3.3 The friction between two surfaces decreases with the increase in the weight of a body.
Correct Statement: The friction between two surfaces increases with the increase in the weight of a body.
3.4 The friction offered by the wheels is called sliding friction.
Correct Statement: The friction offered by the wheels is called rolling friction.
3.5 The friction increases with the increase in the area of contact at the two surfaces.
Correct Statement: The friction is independent of the area of contact at the two surfaces.
