Page 125 - Viva ICSE Science 4 : E-book

TIME TO REVISE

Tick () the correct option.
1. Running fan makes squeaking sound because of (speed/friction).
2. Excess friction will make it (diffi cult/easy) to ride a bicycle on road.

Sometimes we also need to increase the friction between the surfaces that are in touch.

For this, we need to increase the roughness of the surfaces. For example, shoes are
grooved and tyres are treaded to increase the friction so that they get better grip with

the ground.

ACTIVITY TIME

Holding up rice in a bottle with friction
Aim:

To understand the force of friction by inserting a pencil into a bottle containing rice
You Need:

A light-weight bottle with its lid, a bowl of uncooked rice, a
pencil
What to Do:
• Take the bottle and fi ll it up with rice.

• Put the lid on the bottle and tap its bottom on the hard
surface to avoid any spaces in between the rice grains.
• Once you are done with this, remove the lid from the bottle
and insert the pencil down into the bottle to touch the
bottom of the rice.
• Now, try to pull out the pencil and observe what happens.

Observation:
You will observe that the bottle will also come up along with the pencil when pulled.
Result:

The rice fi rmly holds on to the pencil due to the force of friction.

TERMS TO KNOW

1. Friction: A type of force that is exerted by the surface when an object moves across it

2. Motion: The act of movement
3. Lubricants: Things which help in smoothening the movement of objects

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