3. Force can change the shape of an object. Give two examples.
4. The force of friction is more between rough surfaces and less between smooth surfaces.
Why?
5. How can you say that friction acts in a direction opposite to motion?
6. What is rolling friction?
C. Long Answer Questions.
1. What is static friction? Explain with the help of an example.
2. State three advantages of friction.
3. State an example from daily life when force is used:
(a) as a pull (b) as a push (c) to change the direction
(d) to change the shape
4. Give two examples where friction produces heat.
5. What would happen if there was no friction in life?
D. Explain the following terms.
1. Force 2. Friction
3. Sliding friction
E.
Give reasons.
Answers
Answer:
3. Stretching of a rubber band and kneading of wheat flour while making chhappati.
4.This is because of the irregularities on surfaces. In rough surfaces , the quantity of irregularities is high so, when we push (kick) a ball on rough surfaces it stops quickly. But in case of smooth surfaces , the quantity of irregularities is low (or we can also say 'almost no irregularities').So, when we push a ball on a smooth surface, the ball rolls more as compared to rough surfaces.
5.We can say that friction acts opposite to motion by this way : When we push a ball it stops because a opposite force makes the ball stop that force is known as friction or frictional force.
6.Static friction is the frictional force between the surfaces of two bodies (objects) when they are not in motion with respect to each other. For example :- A table, i.e. the table is in rest , if we want to push it doesn't move until we give we higher level of force. This is because the force of friction holds the with a level of force and we push it with a greater force (higher than the force of friction) , it started to move.
7. Three advantages of friction are as follows :-
- Friction enables us to move. If there is no friction , we can't move, i.e., we can't move.
- Friction enables us to write. If there is no friction we can't write.
- Friction enables us to stop things. If there is no friction, we can't stop even a ball.
8.
- As a pull ,the two examples are given below :-
- Opening a drawer , by pulling.
- Opening a door , by pulling.
2. As a push, the two examples are
given below :-
- Closing a door , by pushing.
- Kicking a football , by pushing.
3. To change a direction, the two
examples are given below :-
- Hitting a cricket ball , by pushing.
- Kicking a football which is already moving , by pushing.
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