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.

force exerted, as in moving a body, or changing the direction of its motion; impressed force.

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.

Inertness; inactivity.

dead force; force doing no active work, but only producing pressure.

vital force.

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 , 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.