Mass:
The mass of a body is the quantity of matter contained in it. It is a basic property of matter. It does not depend on the temperature, pressure or location of the body in space. The SI unit of mass is kilogram (kg).
Weight:
The weight of a body is the force with which a body is pulled towards the centre of the earth. It is equal to the product of the mass (m) of the body and the acceleration due to gravity (g) of the earth on body.
Thus W = mg
As the value of ‘g’ changes from place to place, so the weight of a body is different at different places.
The SI unit of weight is newton (N).
Differences between mass and weight:
| Mass | Weight |
| 1. Mass is the measure of inertia. 2. It is a scalar quantity. 3. It is a constant quantity. 4. It cannot be zero for a body. 5. It is an essential property of material bodies. 6. It is not affected by the presence of other bodies. 7. Its units are gram, kilogram, etc. | 1. Weight is the measure of gravity. 2. It is a vector quantity. 3. It varies from place to place. 4. Weight of a body is zero at the centre of the earth. 5. It is not an essential property. 6. It is affected by the presence of other bodies. 7. Its units are dyne, newton, etc. |
Inertial and Gravitational Masses
Inertial Mass: The mass of a body which determines its inertia in translatory motion is called its inertial mass. It is defined by Newton’s second law of motion and is equal to the ratio of the external force applied on the body to the acceleration produced in it.
By Newton’s second law, F=ma, where m is the inertial mass.
Gravitational Mass: The mass of a body which determines the gravitational pull acting upon it due to the earth is called its gravitational mass. It is defined by Newton’s law of gravitation.
F = GMmg/r2
where, mg is the gravitational mass.