n. 速度（velocity的复数）

Velocity \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. v['e]locit['e].]
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.

Note: 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}.

Note: 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.