Page 126 - Viva ICSE Science 4 : E-book

QUICK LOOK

1. Force of friction develops when an object touches or rubs against a surface.
2. Friction either slows down or completely stops the object from moving.

3. If there is no friction then things will keep moving. But if there is too much of friction,
things will not move at all.
4. Friction is useful in many ways.
• It prevents us from slipping while walking.
• It helps us to hold many things.

• It helps vehicles to move or stop.
5. Friction also causes some problems.
• It can cause wear and tear of machine parts.

• It gives rise to unwanted heat.
• Extra energy is needed to keep objects moving.
6. Friction can be reduced by using oil, grease, powder, wheels or by polishing.

7. Friction can be increased by increasing roughness of the surfaces.

EXERCISES

A. Fill in the blanks.

1. Friction is a force that ____________ motion.

2. Friction provides a grip that is necessary for ____________ and ____________.

3. Materials like oil and grease used to reduce friction are called ____________.

4. Friction between the ____________ and the ____________ helps the car to
stop when brake is applied.

5. Tyres of vehicles are treaded to increase ____________.

B. Mark (T) for true and (F) for false statements.

1. Friction is a force that occurs only between solids.

2. Friction occurs when surfaces touch each other.

3. The smaller the object, the greater is the friction.

4. Heat by lamp or electric stove is because of friction.

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