# vis, virial

#### (Latin: strength, force, vigor; vital force; energy)

Clausius virial theorem
In physics, a theorem stating that the total kinetic energy of a system of particles whose positions and velocities are bounded, averaged over a long period of time, will equal the virial of the system.
virial
1. A certain function relating to a system of forces and their points of application, first used by Rudolf Clausius in the investigation of problems in molecular physics.
2. In physics, half the product of the stress due to the attraction or repulsion between two particles multiplied by the distance between them.

Coined by the German mathematical physicist, Rudolf Julius Emmanuel Clausius (1822-1888), a founder of thermodynamics; including, major advances in electrolysis and kinetic theory of gases.

3. Etymology: from the stem of Latin vires, plural of vis, "strength"; and by extension, "force" or "energy".
virial theorem
1. A theorem stating that the average kinetic and potential energies of a system are related to the system's total energy and internuclear separation. 2. The relation between the binding energy and kinetic energy of a system in equilibrium.
virial-theorem mass
In astronomy, the mass of a star cluster or cluster of galaxies that is derived from the mean motions.