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Virtual velocity
(gcide) | Velocity \Ve*loc"i*ty\, n.; pl. Velocities. [L. velocitas,
from velox, -ocis, swift, quick; perhaps akin to volare to
fly (see Volatile): cf. F. v['e]locit['e].]
[1913 Webster]
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.
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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.
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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.
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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 to 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.
[1913 Webster]
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.
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Syn: Swiftness; celerity; rapidity; fleetness; speed.
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Virtual velocity
(gcide) | Virtual \Vir"tu*al\ (?; 135), a. [Cf. F. virtuel. See Virtue.]
1. Having the power of acting or of invisible efficacy
without the agency of the material or sensible part;
potential; energizing.
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Heat and cold have a virtual transition, without
communication of substance. --Bacon.
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Every kind that lives,
Fomented by his virtual power, and warmed. --Milton.
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2. Being in essence or effect, not in fact; as, the virtual
presence of a man in his agent or substitute.
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A thing has a virtual existence when it has all the
conditions necessary to its actual existence.
--Fleming.
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To mask by slight differences in the manners a
virtual identity in the substance. --De Quincey.
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Principle of virtual velocities (Mech.), the law that when
several forces are in equilibrium, the algebraic sum of
their virtual moments is equal to zero.
Virtual focus (Opt.), the point from which rays, having
been rendered divergent by reflection of refraction,
appear to issue; the point at which converging rays would
meet if not reflected or refracted before they reach it.
Virtual image. (Optics) See under Image.
Virtual moment (of a force) (Mech.), the product of the
intensity of the force multiplied by the virtual velocity
of its point of application; -- sometimes called {virtual
work}.
Virtual velocity (Mech.), a minute hypothetical
displacement, assumed in analysis to facilitate the
investigation of statical problems. With respect to any
given force of a number of forces holding a material
system in equilibrium, it is the projection, upon the
direction of the force, of a line joining its point of
application with a new position of that point indefinitely
near to the first, to which the point is conceived to have
been moved, without disturbing the equilibrium of the
system, or the connections of its parts with each other.
Strictly speaking, it is not a velocity but a length.
Virtual work. (Mech.) See Virtual moment, above.
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