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/ mm2

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.