Gravitational force :
- Universal force.
- Acts between two objects on the earth.
- Also act between any two objects in the universe.
- Phenomenon of gravitation was discovered by Sir Isaac Newton.
- Earth must be attracting the Every object towards itself and this attractive force must be directed towards the center of the earth.
- Every object falls vertically downwards.
Introduction to scientist : Sir Isaac Newton :
- Gave his laws of motion, equations of motion and theory of gravity in his book Principia.
- With his theory of gravity, mathematically derived Kepler’s laws.
- Work in light, heat, sound and mathematics.
- Invented a new branch of mathematics - Calculus
- First scientist to construct a reflecting telescope.
Force and Motion :
- Force is necessary to change the speed as well as the direction of motion of an object.
Circular motion and Centripetal force :
- A force acts on any object moving along a circle and it is directed towards the centre of the circle. This is called the Centripetal force.
- ‘Centripetal’ means centre seeking.
- Object tries to go towards the centre of the circle because of this force.
- Moon, which is the natural satellite of the earth, goes round it in a definite orbit.
- The direction of motion of the moon as well as its speed constantly changes during this motion.
- moon to go around the earth, there must be a force which is exerted on the moon.
- This force must be exerted by the earth which attracts the moon towards itself.
- Similarly, the Sun must be attracting the planets, including the earth, towards itself.