Friction Class 8 Worksheet Science Chapter 9

Q.1. Why do kabaddi players rub their hands with dry soil?

Kabaddi players rub their hands with soil for a better grip on their opponents.

Q.2. When does sliding friction come into play?

Sliding friction comes into play when an object is sliding over another.

Q.3. What is done to increase friction between the tyres and road?

The tyres of the vehicle are treaded to increase friction.

Q.4. Name the force responsible for wearing out car tyres.

The frictional force is responsible for the wearing of car tyres.

Q.5. Explain why sportsmen use shoes with spikes.

Sportsmen use shoes with spikes because spikes increase the force of friction between the shoes and the ground and give them a better grip while running.

Q.6. Can we reduce friction to zero by polishing surfaces or using a large amount of lubricants?

Friction can never be entirely eliminated. No surface is perfectly smooth. Some irregularities are always there.

Q.7. What is rolling friction?

When one body rolls over the surface of another body, the resistance to its motion is called rolling friction.

Q.8. Why do tyres of cars wear out gradually?

The tyres of cars wear out gradually due to friction between the surface tyres and the surface of the road.

Q.9. Explain why the sliding friction is less than the static friction.

Friction is caused by the interlocking of irregularities in the two surfaces. When the object starts sliding, the contact points on its surface do not get enough time to lock into the contact points on the floor. So, the sliding friction is slightly smaller than the static friction and we find it somewhat easier to move the object already in motion than to get it started.

Q.10. When we strike a matchstick against the rough surface, it catches fire. Give reason.

When we strike a matchstick against the rough surface, then the friction between the head of the matchstick and rough surface produces heat. This heat burns the chemicals present on the head of the matchstick due to which the matchstick catches fire.

Q.11. What is a spring balance?

Spring balance is a device used for measuring the force acting on an object. It consists of a coiled spring that gets stretched when a force is applied to it. Stretching of the spring is measured by a pointer moving on a graduated scale. The reading on the scale gives the magnitude of the force.

Q.12. Why do car wheels often spin on icy roads?

A car spins on an icy road because the treads of the car can no longer maintain the proper friction to keep it moving. Due to ice, the friction reduces and the car spins.

Q.13. Iqbal has to push a lighter box and Seema has to push a similar heavier box on the same floor. Who will have to apply a larger force and why?

Force of friction arises because of the interlocking of irregularities on the two surfaces in contact. When a heavy object is placed on the floor, the interlocking of irregularities on the surfaces of box and floor become strong. This is because the two surfaces in contact are pressed harder. Hence, more force is required to overcome the interlocking. Thus, to push the heavier box, Seema has to apply a greater force than Iqbal.

Q.14. You spill a bucket of soapy water on a marble floor accidentally. Would it make it easier or more difficult for you to walk on the floor? Why?

We are able to walk because of the friction present between our feet and the ground. In order to walk, we push the ground in the backward direction with our feet. The force of friction pushes it in the forward direction and allows us to walk. The force of friction between the ground and feet decreases when there is soapy water spilled on the floor. Hence, it becomes difficult to walk on the soapy floor.

Q.15. Why will a pencil write on paper, but not on a glass?

We are able to write on paper because there is friction between the tip of the pencil and the paper. We are not able to write on a glass because the glass surface is very smooth due to which friction between the tip of the pencil and the glass surface is less. This friction is not enough to rub off black graphite particles from the tip of a pencil.