Vĭs, n.

n. [Lat.] Force; power.

Vis impressa (Mech.), force exerted, as in moving a body, or changing the direction of its motion; impressed force. [Obs.] — Vis inertiae. (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. Vis inertiae 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 (Mech.), dead force; force doing no work, but only producing pressure. [Rare.] — Vis vitalis (Physiol.), vital force. — Vis viva (Mech.), living force; the force of a body moving against resistance, or doing work, in distinction from vis mortua, or dead force. It is expressed by the product of the mass of a body multiplied by the square of its velocity. — Principle of vis viva, 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 whilst the work is doing.