Mass is a measure of how much matter is contained within an object. Its SI unit is the kilogram.

The mass of an object can be found by pushing on it with a known force F and dividing the size of that force by the resulting acceleration (a).[1]

[math] m = \frac {F}{a} [/math]

Mass is different from weight (force) in that its value does not change if gravity changes. For example, on Earth, where the acceleration due to gravity is 9.8 m/s2, a person who has 60 kg of mass weighs 588 Newtons (132 lbs). On the moon, where the acceleration due to gravity is about 1/6 of what it is on Earth, that same 60 kg person weighs just 98 Newtons (~22 lbs).

To read more about the SI unit of mass, the kilogram, click here.


  1. Sears, Zemansky, and Young, Fifth Edition University Physics. Addison-Wesley Publishing Company, 1979.

Authors and Editors

Semaa Amin, James Jenden, Kailyn Stenhouse, Jason Donev