The amount of matter in an object is referred to as its mass. Although the mass of an object is one of the factors that determines its weight, it is a different property. An object's weight is affected by gravity and can vary depending upon its location relevant to another object exerting a gravitational pull on it; however, an object's mass remains constant, even when there is no gravity acting upon it, such as in space beyond the Earth's gravitational field.
The amount of an object's mass contained within the physical space it occupies, which is its volume, determines its density. Like weight, the density of an object is a different property than its mass. The density of an object is equal to its mass divided by its volume. While an object's mass is measured in grams or kilograms, its density measurement is expressed as a ratio of grams to volume, such as grams per cubic centimeter, or g/cm3.
When a force is applied to an object, the degree of its acceleration in reaction to that force is determined by the object's mass. A greater degree of mass in an object gives it a greater degree of what is termed its inertia. The degree that an object will resist a force acting upon it, or to remain in motion once it is moving, is related to its inertia, and it is therefore also dependent upon the amount of mass that the object contains.