CLASS - 4 // SUBJECT - SCIENCE // LESSON 12 // FRICTION AS A FORCE //

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LESSON 12

FRICTION AS A FORCE

1.  Define friction

Friction is force that opposes motion. It is caused by the irregularities on the two surfaces in contact. Objects with a smooth surface have less friction that object with rough surface.

 

2.  Why is it harder to move a box on the carpet that on a wooden floor?

It is harder to move a box on the carpet than on a wooden floor as there is more friction between the carpet and the box. Heavy objects have more friction than light objects.

 

3.  Write three useful effects of friction.

a.   Friction helps us to walk

b.   Friction enables vehicles to move ahead

c.   Friction helps us to hold things.

 

4.  Write down three disadvantages of friction.

a.   Friction opposes motion in objects. So we need to spend energy to keep them in motion,

b.   Friction causes the soles of our shoes, tires of vehicles, and parts of machines to wear out.

c.   Friction between moving parts in machines produces heat. This excess heat can damage the machines,

 

5.  Why is grease used in various machines?

Lubricating oil is applied on moving parts of machines that move over one another. This smoothens their surfaces and reduces the friction between them. Grease and engine oils are used to reduce friction in various machines.

 

6.   Why do suitcases now a days come with wheels?

Wheels make it easy to move heavy objects because it reduces friction. That is why suitcases nowadays come with wheels. This helps to minimize effort.

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