eiginleikamass

Eiginleikamass, or eiginleikamassi (intrinsic mass), is a term encountered in Icelandic-language discussions of physics to denote the mass that is an intrinsic property of a particle or system, typically corresponding to the invariant or rest mass.

In physics, the invariant (rest) mass is a scalar quantity that does not depend on the observer’s frame of reference. For a particle or system with total energy E and momentum p, the invariant mass M satisfies M^2 c^4 = E^2 − (pc)^2, where c is the speed of light. This mass is the same in all inertial frames and is what is usually meant in discussions of the mass of fundamental particles.

Eiginleikamass is sometimes used interchangeably with rest mass in Icelandic texts, but terminology can vary. Some sources distinguish rest mass (hvíldarmassi) from a broader notion of intrinsic properties that contribute to a system’s mass, especially for composite systems where binding energy and internal motion affect the total invariant mass.

For example, elementary particles have characteristic rest masses (e.g., electron ≈ 9.11 × 10^−31 kg; proton ≈ 1.67 × 10^−27 kg). For bound systems, the invariant mass can differ from the sum of constituent rest masses due to binding energy and internal dynamics.

See also: Mass, Invariant mass, Rest energy, Rest mass. Note that Icelandic terminology varies, and some texts may prefer hvíldarmassi for rest mass.