Mass and Weight

Mass (m): The amount of matter in an object. In the International Standard of Units (SI), the standard unit of measuring the mass is the “Kilogram (kg)”. It is the mass of a block made of Platinum-Iridium alloy (90% Platinum & 10% Iridium), measured at melting point of ice, located at International Bureau of Weights and Measures, Paris.

Weight (W): The force with which an object is attracted towards the centre of the earth. According to Sir Issac Newton, force is the product of mass and acceleration. Therefore, weight of an object is the product of its mass (m) and acceleration due to gravity (g = 9.81 m/sec²) i.e., W = mg. In the International Standard of Units (SI), the standard unit of measuring the weight is the “Newton (N)”.

A Newton (N) is the force required to move an object of mass 1 kilogram at the rate of 1 m/sec² acceleration, N = 1 kg-m/sec².

An object of mass 10 kg, weighs 98 N on earth and 16 N on moon (gravity on moon is approximately one-sixth the gravity on earth). Often we see the usage of kg for unit of weight, but for scientific calculations, the unit of weight is strictly N.

Following are the different units of measuring the mass and weight.

Unit	Equivalent mass		Unit	Equivalent weight
Grain	0.000 065 kg		Dyne (g-cm/sec2)	0.000 01 N
Carat	0.000 2 kg		kgf (kilogram-force)	9.81 N
Gram	0.001 kg		kN (kilo-Newton)	1 000 N
Dram	0.002 kg
Ounce	0.028 kg
Pound	0.454 kg
Ton	907 kg
Metric Ton	1 000 kg