Chapter 10
Gravitation
Introduction
Gravitational force of Earth:
- If we release a small stone without pushing it from a height it accelerates towards Earth. The stone is when accelerated towards earth, means some force is acting on it.
- The force which pulls the object towards the centre of earth is known as gravitational force of the earth. Here, stone also attracts the earth.
- It means every object in universe attracts every other object.
- When a body undergoes circular motion, it experiences a force that acts towards the centre of the circle. This centre-seeking force is called a centripetal force.
Universal Law of Gravitation
- According to the universal law of gravitation, every object attracts every other object with a force.
- This force is directly proportional to the product of their masses.
- This force is inversely proportional to the square of distances between them.
From the above equation we can rewrite them as the following:
If we remove the proportionality, we get proportionality constant G as the following:
According to, Newton’s universal Law of gravitation
G = Fr2/ m1 m2
SI Unit: Nm2 kg-2
Value of G = 6.673 × 10-11 Nm2 kg-2
The proportionality constant G is also known as the Universal Gravitational Constant.
Importance of universal law of gravitation
It explains:
- the force that binds us to the earth.
- the motion of moon around the earth
- the motion of planets around the sun.
- the tides due to the moon and the sun.