Mass is an inertial property. Inertia is sensed when a bowling ball is pushed horizontally on a level, smooth surface. This is quite distinct from<unk> ,” which is the downwards gravitational force of the bowling ball that one must counter when holding it off the floor. Unless relativistic effects apply, mass is an unchanging, universal property of matter that is unaffected by gravity.<unk>  on the other hand, is a property of matter that is entirely dependent upon the local strength of gravity. For instance, an astronaut’s<unk>  on the Moon is one-sixth of that on the Earth, whereas his mass has changed little during the trip. Consequently, wherever 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 billiards 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.
In the physical sciences, the terms “mass” and<unk> ” are rigidly defined as separate measures in order to enforce clarity and precision. In everyday use, given that all masses on Earth have<unk>  and this relationship is usually highly proportional,<unk> ” often serves to describe both properties, its meaning being dependent upon context. For example, in commerce, the “net<unk> ” of retail products actually refers to mass and is properly expressed in pounds (U.S.) or kilograms (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<unk> ; that is, the force due to gravity. Before the late twentieth century, this distinction was not as strictly applied, even in technical writing, so that expressions such as “molecular<unk> ” (for molecular mass) are still seen.
Because mass and<unk>  are separate quantities, they have different units of measure. In the International System of Units (SI), the kilogram is the unit of mass, and the newton is the unit of force. The non-SI kilogram-force is also a unit of force typically used in the measure of<unk> . Similarly, the avoirdupois pound, used in both the Imperial system and U.S. customary units, is a unit of mass and its related unit of force is the pound-force. An object with a mass of one kilogram will accelerate at one meter per second squared (about one-tenth the acceleration due to Earth’s gravity) when acted upon by a force of one newton.
Mass versus weight
Molecular mass
Extraction ratio
Gas constant
Spin quantum number
Gibbs free energy
Concentration
Density