Ve*loc"i*ty (?), n.; pl.
Velocities (#). [L. velocitas, from velox,
-ocis, swift, quick; perhaps akin to v&?;lare to fly (see
Volatile): cf. F. vélocité.]
1. Quickness of motion; swiftness; speed; celerity;
rapidity; as, the velocity of wind; the velocity of a planet
or comet in its orbit or course; the velocity of a cannon ball; the
velocity of light.
&fist; In such phrases, velocity is more generally used than
celerity. We apply celerity to animals; as, a horse or an
ostrich runs with celerity; but bodies moving in the air or in
ethereal space move with greater or less velocity, not
celerity. This usage is arbitrary, and perhaps not universal.
2. (Mech.) Rate of motion; the relation of
motion to time, measured by the number of units of space passed over by a
moving body or point in a unit of time, usually the number of feet passed
over in a second. See the Note under Speed.
Angular velocity. See under Angular. -
- Initial velocity, the velocity of a moving body at
starting; especially, the velocity of a projectile as it leaves the mouth
of a firearm from which it is discharged. -- Relative
velocity, the velocity with which a body approaches or
recedes from another body, whether both are moving or only one. --
Uniform velocity, velocity in which the same number
of units of space are described in each successive unit of time. --
Variable velocity, velocity in which the space
described varies from instant, either increasing or decreasing; -- in the
former case called accelerated velocity, in the latter,
retarded velocity; the acceleration or retardation itself being also
either uniform or variable. -- Virtual
velocity. See under Virtual.
&fist; In variable velocity, the velocity, strictly, at any given
instant, is the rate of motion at that instant, and is expressed by the
units of space, which, if the velocity at that instant were continued
uniform during a unit of time, would be described in the unit of time;
thus, the velocity of a falling body at a given instant is the number of
feet which, if the motion which the body has at that instant were continued
uniformly for one second, it would pass through in the second. The
scientific sense of velocity differs from the popular sense in being
applied to all rates of motion, however slow, while the latter implies more
or less rapidity or quickness of motion.
Syn. -- Swiftness; celerity; rapidity; fleetness; speed.
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Webster Unabridged