<P> On Earth, a swing seat can demonstrate this relationship between force, mass, and acceleration . If one were to stand behind a large adult sitting stationary on a swing and give him a strong push, the adult would temporarily accelerate to a quite low speed, and then swing only a short distance before beginning to swing in the opposite direction . Applying the same impetus to a small child would produce a much greater speed . </P> <P> Mass is (among other properties) an inertial property; that is, the tendency of an object to remain at constant velocity unless acted upon by an outside force . Under Sir Isaac Newton's 331 - year - old laws of motion and an important formula that sprang from his work, F = ma, an object with a mass, m, of one kilogram will accelerate, a, at one meter per second per second (about one - tenth the acceleration due to earth's gravity) when acted upon by a force, F, of one newton . </P> <P> Inertia is seen when a bowling ball is pushed horizontally on a level, smooth surface, and continues in horizontal motion . This is quite distinct from its weight, which is the downwards gravitational force of the bowling ball one must counter when holding it off the floor . The weight of the bowling ball on the Moon would be one - sixth of that on the Earth, although its mass remains unchanged . Consequently, whenever the physics of recoil kinetics (mass, velocity, inertia, inelastic and elastic collisions) dominate and the influence of gravity is a negligible factor, the behavior of objects remains consistent even where gravity is relatively weak . For instance, billiard balls on a billiard table would scatter and recoil with the same speeds and energies after a break shot on the Moon as on Earth; they would, however, drop into the pockets much more slowly . </P> <P> In the physical sciences, the terms "mass" and "weight" are rigidly defined as separate measures, as they are different physical properties . In everyday use, as all everyday objects have both mass and weight and one is almost exactly proportional to the other, "weight" often serves to describe both properties, its meaning being dependent upon context . For example, in retail commerce, the "net weight" of products actually refers to mass, and is expressed in mass units such as grams or ounces (see also Pound: Use in commerce). Conversely, the load index rating on automobile tires, which specifies the maximum structural load for a tire in kilograms, refers to weight; that is, the force due to gravity . Before the late 20th century, the distinction between the two was not strictly applied in technical writing, so that expressions such as "molecular weight" (for molecular mass) are still seen . </P>

How to measure mass and weight of an object