MASS AND WEIGHT

Mass

Mass is the amount of matter contained in a body. Mass of a body is the measure of inertia. Mass is a scalar quantity. Its unit is kg in SI system and gram in C.G.S. system. Mass of a body does not vary with position and remains the same everywhere. It is measured by a beam balance.

Weight

It is the force acting on a body due to gravity.

Weight = mass × acceleration due to gravity

W = mg

Weight is a vector quantity. S.I. unit of weight is newton or kgwt Weight varies from place to place. Weight of a body is maximum at the poles and minimum at the equator (∵ g is minimum at the equator and maximum at the poles).

Since gravitational force decreases with height, the weight of a body is less on the top of a mountain compared to that at the sea level. Weight of a body is measured by a spring balance. The dimensional formula of weight = [ M1 L1 T-2 ]

EXAMPLE

A a coconut of mass 1 kg falls from a tree. find its weight (Take acceleration due to gravity = 9.8 m s-2)

SOLUTION

Mass = 1 kg

∴ weight = 1 kg × 9.8 m s-2 = 9.8 N

Difference between Mass and Weight

Mass weight
It is the measure of matter contained in body. It is the force with which a body is attracted towards  the centre of the earth.
It magnitude does not change from place to place. It changes with change in acceleration due to to gravity.
It is measured with the help of a physical balance. It is measured with the help of a spring balance.
It is a scalar quantity. It is a vector quantity.
It is measured in units of gram or kilogram. It is measured in units of dyne or newton.