Page 86 - text book form physics kssm 2020

Newton’s Universal Law of Gravitation states that the File
gravitational force between two bodies is directly proportional to
the product of the masses of both bodies and inversely proportional The value of gravitational
to the square of the distance between the centres of the two bodies. constant, G can be determined
through experiment.
Newton’s Universal Law of Gravitation
can be expressed as follows:

SMART INFO
SMART
Gm m 2
1
Gm m 2 F =
1
F = 2 r 2
r Two bodies of masses m
1
F = gravitational force between two bodies and m that are separated at
2
m = mass of fi rst body a distance of r, experience
1
m = mass of second body a gravitational force of F
2
r = distance between the centre of the fi rst body and the centre respectively.
of the second body
2
–2
G = gravitational constant (G = 6.67 × 10 –11 N m kg )
If you know the masses of two bodies and the distance between the centres of the two bodies,
you can calculate the magnitude of the gravitational force between the two bodies. Study the
examples given.
Example 1

Calculate the gravitational force between a durian and the Earth.
Mass of durian = 2.0 kg
24
Mass of the Earth = 5.97 × 10 kg
Distance between the centre of the durian and the centre of the Earth
6
= 6.37 × 10 m
Figure 3.6
Solution:
14243 6
1
m = 5.97 × 10 kg
Step m = 2.0 kg 24
2
List the given information in symbols. r = 6.37 × 10 m 2 –2
–11
G = 6.67 × 10
N m kg
123 Gm m
Step Gravitational force,
Identify and write down the formula used. F = r 1 2 2
24
Step (6.67 × 10 –11 ) × 2.0 × (5.97 × 10 )
Substitute numerical values into the formula 123 F = (6.37 × 10 )
6 2
and perform the calculations. = 19.63 N

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