JSS 1: Gravitation and weightlessness
Gravitation
Effects of gravitational pull
Gravitation is defined as a natural phenomenon by which all physical bodies attract one another.
Gravity: This is the force that attracts a body towards the centre of the earth.
Gravitational pull
Gravitational pull is the force of attraction to the earth. The gravitational pull on the moon is about one-sixth of that of the Earth and that is why astronauts seem lighter and need special boots and clothes to walk on the moon
1. Gravitational pull affects the weight of an object
2. It helps human beings to stand well on the earth
3. It keeps the planets of the solar system in their positions
4. It helps the moon to keep revolving around the earth
5. It helps in the formation of tides
Centre of gravity (C.G.)
The Centre of gravity is the average point on an object where the total weight is located.
Weight is the measure of the force of gravity acting on a body.
It is measured using a Spring balance.
The S.I. Unit of weight is Newton (N)
Weight (W) = mass (m) x acceleration due to gravity (g)
W = m x g
Example: The mass of an object is 20kg. Calculate the value of its weight (g=10m/s²)
Solution:
Weight = m x g
= 20 x 10
= 200N
Earth's gravitational force
The earth's gravitational force is a downward force pulling objects towards the center of the earth.
Gravitational force depends on the following factors:
1. The mass of the object
2. The mass of the earth
3. The distance between the center of the object and the earth.
Where:
F = Gravitational force
G = Gravitational constant (6.67 x 10-¹¹)
M = Mass of the earth
m = mass of other object
r = distance between the earth and another object
Weightlessness
Weightlessness is the state of not experiencing the effect of gravity. It is a feeling of not having weight.
Examples of weightlessness:
1. Astronaut in a spaceship
2. People inside the elevator
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