\Vis\, n.
1. Force; power.
2. (Law)
   (a) Physical force.
   (b) 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.]
   (a) 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.
   (b) 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.