Causes of friction

1. Write down the factors on which force of friction depends.
2. How does irregularities of a surface helps the two surfaces in contact stay together?
3. What are the two factors on which force of friction does not depend?
4. Tie a string around a brick. Pull the brick by a spring balance . You need to apply some force. Note down the reading on the spring balance when the brick just begins to move. It gives you a measure of the force of friction between the surface of the brick and the floor.
Now wrap a piece of polythene around the brick and repeat the activity. Do you observe any difference in the readings of the spring balance in the above two cases? What might be the reason for this difference? Repeat this activity by wrapping a piece of jute bag around the brick. What do you observe?
5. Rahul has to push a lighter box and Rohit has to push a similar heavier box on the same floor. Who will have to apply a larger force and why?
6. What is the direction of force of friction acting on a moving object?
7.Why does a matchstick catch fire when rubbed on the rough surface of the box?

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