NCERT 8th Class CBSE Science: Friction

Question: Friction is a necessary evil. Explain.

Answer: Friction is a necessary evil as several activities cannot be done without friction like-

1. Friction makes it possible for us to walk.
2. Cars and buses are able to move safely because of friction.
3. We would not be able to write without friction.
4. It would not be possible to light a matchstick if there was no friction.
5. Friction causes nails and screws to hold on to walls.

Friction 8th Science – Question: What causes friction?

Answer: Friction occurs when two bodies move on each other. Each surface has some irregularities on it. When two such objects move on each other their irregularities get interlocked and friction arises.

Question: When we gently push a book on a table, it stops after some distance, why?

Answer: When we gently push a book on a table, it stops after some distance because of force of friction, which stops the movement of the book. The friction opposes the movement of book and stops it. Friction always works in opposite direction of the movement of object and opposes the relative movement between the book and the table.

Question: How does the nature of surface effect friction?

Answer: Nature of the surface plays major role in production of friction. The rough surface produces more friction than the smooth surface. The rough surface has more irregularities on it than the smooth surface, so more force is required to overcome the friction caused by irregularities.

Question: Suggest some methods to reduce friction.

Answer: Some methods to reduce friction are as follows:

1. Lubricating oil and grease are used in machines to reduce friction between moving parts.
2. Some machines use air cushion for reducing friction because use of oil is not ideal in such machines.
3. Graphite powder is used in some machines to reduce friction.
4. Ball bearing coverts sliding friction into rolling friction. You have read that rolling friction is less than sliding friction. Thus, ball bearing helps in reducing friction.

Question: Suggest some methods to increase friction.

Answer: Some methods to reduce friction are as follows:

1. Rubber grips are put on bicycle handles, electrical tools and on many other tools. Increased friction helps in giving better grip on these objects.
2. A surface can be made rough with the help of sand paper; in order to increase friction.
3. Soles of shoes are made rough to increase friction. This helps in providing better grip on surface while walking.
4. Treads of tyres are deliberately made so that a good road grip can be achieved with the help of friction.
5. Holding a bottle cap with a thick towel helps in increasing friction. Increased friction makes it easier to open the bottle cap.