A measure of the amount of matter in a body. It can also be seen as a measure of a body’s inertia or resistence to change in motion, or the degree of acceleration a body acquires when subject to a force (bodies with greater mass are accelerated less by the same force and have greater inertia). Mass is often confused with weight, which is the strength of the gravitational pull on the object (and therefore how heavy it is in a particular gravitational situation), although, in everyday situations, the weight of an object is proportional to its mass.