Page 67 - Physics

Introduction to force

Force of gravity 3. It is a central force (gravitational
The force of gravity is the force of attraction force between two objects act along

between objects which have mass. All the line joining the centres of the
objects).
objects having mass are pulled towards 4. It operates over very long distances.
the earth’s centre by the earth’s force of
gravity. It is because of the earth’s force of Your weight on earth is the gravitational
gravity that bodies in the air move towards force that the earth exerts on you. Remember
the earth’s surface despite their sizes. For that gravity is an action-at-a-distance force,
example, fruits fall from a tree because so even when you jump into the air, as
of the earth’s gravitational force. Human shown in Figure 3.4, the earth still exerts
beings can walk properly because of the its gravitational force on you. This is the
force that prevents you from fl ying off on
earth’s force of gravity. The magnitude a spinning earth. The gravity force is also
of the gravitational force exerted on an responsible for keeping a satellite in its
object is referred to as the weight of an orbit around the earth and planets in their
object. It is represented by the symbol w orbits around the sun.
and measured in newton (N). The weight

of an object is the product of its mass, m
and acceleration due to gravity, g.
(
weight w ( )= mass m)×acceleration
duetogravity(g)
Normally it can be written as,

w = mg

Where, w - Weight of object Fg
m - Mass of object
g - Acceleration due to gravity

Weight is defi ned as an attractive force
acting on an object due to gravity. Figure 3.4: A boy jumping

Task 3.1
The weight of an object is equal to the
gravitational force on it. The following After learning about physical quantities,
are properties of the gravitational force: a student argues that mass and weight
1. It is always attractive. represents the same physical quantity.
2. It is the weakest force among the four With reasons, support or oppose this
fundamental forces. argument.

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Physics Form 1 Final.indd 61 16/10/2024 20:56