kokonaismassan

Kokonaismassan, Finnish for “the total mass,” refers to the sum of the masses of all components in a system. In classical mechanics, the total mass M of a closed system is constant and can be obtained by M = Σ m_i. Mass is treated as an additive property, so the mass of a container equals the mass of its contents plus the container’s mass, neglecting energy changes that affect mass.

In relativity, the concept is refined by the invariant (rest) mass of a system. The invariant mass is defined from the system’s total energy E and momentum p via M^2 c^4 = E^2 − (pc)^2. If the system is at rest (p = 0), then E = M c^2. Internal kinetic energy and binding energy mean that the invariant mass can differ from the simple sum of the rest masses of the parts; binding energy (negative with respect to the rest-mass sum) reduces the invariant mass.

In practice, total mass is a fundamental quantity across fields. It is used in engineering for mass budgeting and system design, in astrophysics for estimating the mass of stars, planets, and galaxies through dynamics or gravitational effects, and in chemistry where mass is conserved to high accuracy in reactions. Measurements typically rely on balances and scales, or on indirect dynamical methods in systems where direct weighing is impractical.

See also: mass, center of mass, mass-energy equivalence, binding energy, conservation of mass.