Vis inertiae

Vis Vis, n. 1. Force; power. [1913 Webster]

2. (Law) (a) Physical force. (b) Moral power. [1913 Webster]

{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. [1913 Webster]