The mass of an object is a measure of an object's resistance to acceleration, sometimes also called "inertia". A mountain has typically more mass than a rock, for instance. Mass should not be confused with the related but quite different concept of weight. A large mass like the Earth will attract a small mass like a human being with enough force to keep the human being from floating away. "Mass attraction" is another word for gravity, a force that exists between all matter. The unit of mass in the International System of Units is the kilogram, which is represented by the symbol 'kg'. Fractions and multiples of this basic unit include the gram (one thousandth of a kg, symbol 'g') and the tonne (one thousand kg), amongst many others. In some fields or applications, it is convenient to use different units to simplify the discussions or writings.

License information: CC BY-SA 3.0 and GFDL
MPAA: G
Go to source: https://simple.wikipedia.org/wiki/Mass