NCERT Class VIII Science Solutions: Chapter 12-Friction Part 3

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Question 13:

Imagine that an object is falling through a long straight glass tube held vertical; air has been removed completely from the tube. The object does not touch the walls of the tube. Will the object experience any force of friction?

Answer:

No

SHORT ANSWER QUESTIONS

Question 14:

You might have noticed that when used for a long time, slippers with rubber soles become slippery. Explain the reason.

Answer:

When rubber soles are used for a long time, their surfaces become smooth. Hence, the friction between the sole and the floor decreases. Therefore, slippers become slippery

Question 15:

Is there a force of friction between the wheels of a moving train and iron rails? If yes, name the type of friction. If an air cushion can be introduced between the wheel and the rail, what effect will it have on the friction?

Answer:

Yes, rolling friction. If an air cushion is introduced between the wheel and the rails, the friction will decrease.

Question 16:

Cartilage is present in the joints of our body, which helps in their smooth movement. With advancing age, this cartilage wears off. How would this affect the movement of joints?

Answer:

The wearing off of cartilage will increase the friction. As a result the movement of joints will become difficult which may lead to joint pains

Question 17:

While playing tug of war Preeti felt that the rope was slipping through her hands. Suggest a way out for her to prevent this.

As showing in fig is a boys and girls are playing game

Boys and Girls Are Playing Game

As showing in fig is a boys and girls are playing game

Answer:

She may rub soil to increase friction between the rope and her hand.

Question 18:

The handle of a cricket bat or a badminton racquet is usually rough. Explain the reason.

Answer:

To increase friction between handle of the bat and hands, to have a better grip

Question 19:

Explain why the surface of mortar and pestle (silbatta) used for grinding is etched again after prolonged use?

Answer:

To increase friction to make it more effective for grinding again.