What is "vis viva"

Vis \Vis\, n.

1. Force; power.

2. (Law)

   1. Physical force.

   2. Moral power. Principle of vis viva (Mech.), the principle that the difference between the aggregate work of the accelerating forces of a system and that of the retarding forces is equal to one half the vis viva accumulated or lost in the system while the work is being done. Vis impressa [L.] (Mech.), force exerted, as in moving a body, or changing the direction of its motion; impressed force. Vis inerti[ae]. [L.]

      1. The resistance of matter, as when a body at rest is set in motion, or a body in motion is brought to rest, or has its motion changed, either in direction or in velocity.

      2. Inertness; inactivity.

         Note: Vis interti[ae] and inertia are not strictly synonymous. The former implies the resistance itself which is given, while the latter implies merely the property by which it is given.

         Vis mortua [L.] (Mech.), dead force; force doing no active work, but only producing pressure.

         Vis vit[ae], or Vis vitalis [L.] (Physiol.), vital force.

         Vis viva [L.] (Mech.), living force; the force of a body moving against resistance, or doing work, in distinction from vis mortua, or dead force; the kinetic energy of a moving body; the capacity of a moving body to do work by reason of its being in motion. See Kinetic energy, in the Note under Energy. The term vis viva is not usually understood to include that part of the kinetic energy of the body which is due to the vibrations of its molecules.

n. (context physics obsolete English) The product of an object's momentum and the square of its speed.

Vis viva (from the Latin for "living force") is an obsolete scientific theory that served as an elementary and limited early formulation of the principle of conservation of energy. It was the first (known) description of what we now call kinetic energy or of energy related to sensible motions.

Proposed by Gottfried Leibniz over the period 1676–1689, the theory was controversial as it seemed to oppose the theory of conservation of momentum advocated by Sir Isaac Newton and René Descartes. The two theories are now understood to be complementary.

The theory was eventually absorbed into the modern theory of energy though the term still survives in the context of celestial mechanics through the vis viva equation.