In physics, the quantity of Matter in a body regardless of its volume or of any Forcees acting on it. There are two ways of referring to mass, depending on the
laws of physics defining it. The Gravitational mass of a body may be determined by comparing the body on a beam balance
with a set of standard masses; in this way the gravitational factor is eliminated
(see Weight). The Inertial mass of a body is a measure of the body's resistance to acceleration by some
external force. All evidence seems to indicate that the gravitational and
inertial masses are equal. According to the special theory of Relativity, mass increases with speed according to the formula
m = m-sub-0/(square-root(1 - v-squared/c-squared)), where m-sub-0 is the Rest Mass of the body, v its speed, and c the Speed of Light in Vacuum. The theory also leads to the Albert Einstein mass- Energy relation E = mc^2, where E is the energy and m the relativistic mass.