# Newton’s Law of Gravitation | Physics Grade XI

### Gravity and Gravitation

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Newton's Law of Gravitation:
Newton’s law of gravitation states, "Everybody in the universe attracts every other body with a force that is directly proportional to the product of their masses and inversely proportional to the square of their distance".

According to Newton’s law of gravitation,

The force between them is

F α m1 * m2 ……… (i)
And
F α 1/r2 ……... (ii)
Combining Equation (i) and (ii), we get
F α m1m2 / r2
Or, F= Gm1m2 / r2         Where G is constant of proportionality called Universal gravitational constant.

Universal Gravitational Constant (G):
It is defined as the force of attraction between two bodies of unit mass kept at unit distance between their centers.

Properties of G

1. The value of gravitational constant G is independent of the mature or masses of the body.
2. It is unaffected by the change in temperature or pressure
3. It is independent of the directions of the gravitational forces between the two or more masses.
4. The gravitational constant G is independent of the medium in which the masses are placed and the chemical composition of masses.

Inertial mass of a body is the measure of ability of the body to oppose the change in the velocity i.e. acceleration produced by an external force.

Gravitational mass of a body is the measure of the gravitational pull acting on the body. It is given by newton’s law of gravitation,

F = GMm/R2
m = F R2/ GM,   the mass of the body is ‘m’ which is the gravitational mass of the body.

 Inertial Mass Gravitational mass It is the mass of material which measures its inertia It is the mass of the body which determines the gravitational pull acting upon it. It can be measured when the body is in motion It can be measured in the rest position of the body The inertial mass of the body is measured according to Newton’s second law of motion By Newton’s law of gravitation, gravitational mass is measured

Weight:
The weight of the body is defined as the gravitational force with which the object is attracted by the earth towards its center.

 Mass Weight It is the measure of inertia It is the measure of gravity It is a constant quantity It may vary from place to place It is a scalar quantity It is a vector quantity It can never be zero It is zero at places where g = 0 Its SI-unit is kg Its SI-unit is dyne

Gravitational Potential is the amount of work done in bringing the body of unit mass from infinity to a point inside gravitational field.

Gravitational Field strength is the force experienced by a body of unit mass inside the gravitational field.

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