The New Student's Reference Work/Mass
Mass is the name which has been given to the amount of matter in a body. The mass of a body, the amount of matter in a body and the inertia of a body are strictly synonymous terms as used in modern physics. Matter and therefore mass have not been defined in terms of anything simpler; but mass can be measured in terms of many other quantities. Thus mass is equal to the product of volume by density In like manner the mass of a body is equal to the quotient of its weight divided by the acceleration of gravity. A sharp distinction between mass and weight is essential to all clear thinking on this subject. The standard of mass used in ordinary commerce is the mass of a piece of metal kept in the Standard's Office, London, and known as the avoirdupois pound. The standard of mass employed in science is a piece of metal kept at the International Bureau of Weights and Measures at Sèvres, and known as the kilogram. See Inertia.