## Gravitation

Gravitation is the name given to the force of attraction acting between any two bodies of the universe.

### Newton’s low of gravitation

It states the gravitational force of attracting acting between any two bodies of the universe is directly proportional to the product of their masses and is inversely proportional to the square of the distance between them i.e. F = GMm/r.r . Where G is the Universal gravitational constant. The direction of this force F is towards the center of attracting body. M and m is the mass of particle and r is distance between particles. The Newton gravitational force is also known as mutual gravitational interaction, as the forces exerted by two bodies are mutual, equal in magnitude but opposite in direction.

### Characteristic of Gravitational force

According to Newton’s law on gravitation, gravitational force of attraction between two bodies

1) Is dependent of the nature of intervening medium.

2) Gravitational force dependent of the presence or absence of other bodies.

3) Is dependent of nature and size of the bodies, till their masses remain the same and the distance between their centers is fixed.

4) From action and reaction pair i.e. the gravitational force are equal in magnitude and opposite in direction and hence they obey Newton’s third law of motion.

5) The gravitational forces are central forces as they act along the line joining the centers of the two bodies.

6) The gravitational forces are conservation forces.

7) Gravitational force is the weakest force in nature. It is about 1038 times weaker than nuclear forces and 1036 times weaker than the electric forces.

8) The gravitational force is caused by gravitational mass.

### Gravitational constant(G)

It is defined as the force of attraction acting between two bodies each of unit mass, whose centers are placed unit distance apart. The value of G is constant throughout the universe. It is a scalar quantity.

### Gravity

1) It is the force of attraction exerted by earth towards its centre on a body lying on or near the surface of the earth.

2) Gravity is the measure of weight of the body. The weight of the body = mass (m) * acceleration due to gravity (g) = mg

3) The unit of weight of the body will be the same as those of force.

4) Gravity is the vector quantity. It is always directed towards the center of earth.

5) Gravity holds the atmosphere around the earth.