Definition of Mass and Weight

Sometimes much confusion and misunderstanding are created while using the various systems of units in the measurements of force and mass. This happens because of the lack of clear understanding of the difference between the mass and the weight.

The following definitions of mass and weight can be understood easily:

1. Mass: Mass is the amount of matter contained in a given body and does not vary with the change in its geographical position on the earth’s surface. Direct comparison with a standard mass measures the mass of a body by using a lever balance.

2. Weight: Weight is the amount of pull, which the earth exerts upon a given body. Since the pull varies with the distance of the body from the center of the earth, therefore the weight of the body will vary with its geographical position on the earth’s surface (say latitude and elevation). It is thus obvious that the weight is a force.

The earth’s pull in metric units at sea level and 45° latitude has been adopted as one force unit and named as one kilogram of force.
Thus, it is a definite amount of force. But, unfortunately, it has the same name as the unit of mass.
The weight of a body is measured by the use of a spring balance which indicates the varying tension
in the spring as the body is moved from place to place.

Note: The confusion in the units of mass and weight is eliminated, to a great extent, in S.I. Units.

The relation between the mass (m) and the weight (W) of a body is

Weight (W) = Mass × Gravity

W = m × g

Where Weight (W) is measured in newtons (N),

Mass (m) is measured in kilograms (kg) and  ‘g’ is acceleration due to gravity is measured in ms-2.

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