Page 117 - ACTIVE SCIENCE 4 TOC

T ypes Of Forces

Force means a pull or a push. If someone makes an effort to move an object it is
called force. There are forces acting all around us all the time. Force can be of

three types.

1. Gravitational Force 2. Frictional Force 3. Muscular Force

1. Gravitational Force : When we Factual Study
throw something upwards, it will

always fall back on the earth. It • Gravity makes stars burn by squeezing
happens because the earth applies their matter together.
force called gravitational force • Black holes have the strongest
on the object. It always pulls the gravitational pull in the entire universe.
object towards the centre of the
earth. If there were no gravity, we would be floating in the air.

2. Frictional Force : Frictional force always opposes the motion of one

surface across another surface. To experience this force, two forces have to
be in contact.

Less friction is provided by smooth surfaces and more friction by rough
surfaces. Walking on plane ground provides ample friction as compared to
walking on icy surface. This is because ice causes very less friction. So, it is

a good thing for ice skating and sledging.

Factual Study

If you don’t lubricate your
bike regularly with oil, the
friction in the chain and
axle increases. Your bike

will be noisy and difficult

Gravitational Force Ice Skating to ride.

Activity 14.1

Aim : To understand the amount of friction applied.

Materials Required : An empty box, thread, smooth table, sugar.

Procedure : 1. Take a box and tie a thread around the box.
2. Move the empty box on the table with the help of a thread.

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