Vis

(vis.) [L., force.] (Phys.) Vis inert ise, the force of inactivity. The word was employed by Newton to signify the power implanted in all matter, by which it resists any change endeavored to be made in its state; that is, the power by which it becomes difficult to change the state of rest or motion. The property of matter which is set forth in the law of inertia is, however, simply absolute pa ivene ; there is no disposition in matter to resist being put in motion when at rest; in other words, vis ine rtiæ does not exist. The phrase has been a fertile source of error.- Vis viva. A measure of the kinetic energy, or inherent work of a moving body. It is the product of the ma by the square of the velocity. The chief properties of the vis viva are the following:-If a system of bodies be under the action of no external forces, the vis viva of the system is constant. If abo dy move in any manner, its vis viva at any instant is equal to the vis viva of the whole ma , as if it were collected at the centre of gravity, plus the vis viva round the centre of gravity considered as a fixed point. [s. 941]