DICT.TW Dictionary Taiwan

 Mo·ment n.
 1. A minute portion of time; a point of time; an instant; as, at that very moment.
    In a moment, in the twinkling of an eye.   --1 Cor. xv. 52.
 2. Impulsive power; force; momentum.
    The moments or quantities of motion in bodies.   --Berkley.
 Touch, with lightest moment of impulse,
 His free will.   --Milton.
 3. Importance, as in influence or effect; consequence; weight or value; consideration.
    Matters of great moment.   --Shak.
    It is an abstruse speculation, but also of far less moment and consequence of us than the others.   --Bentley.
 4. An essential element; a deciding point, fact, or consideration; an essential or influential circumstance.
 5. Math. An infinitesimal change in a varying quantity; an increment or decrement. [Obs.]
 6. Mech. Tendency, or measure of tendency, to produce motion, esp. motion about a fixed point or axis.
 Moment of a couple Mech., the product of either of its forces into the perpendicular distance between them.
 Moment of a force. Mech. (a) With respect to a point, the product of the intensity of the force into the perpendicular distance from the point to the line of direction of the force. (b) With respect to a line, the product of that component of the force which is perpendicular to the plane passing through the line and the point of application of the force, into the shortest distance between the line and this point. (c) With respect to a plane that is parallel to the force, the product of the force into the perpendicular distance of its point of application from the plane.
 Moment of inertia, of a rotating body, the sum of the mass of each particle of matter of the body into the square of its distance from the axis of rotation; -- called also moment of rotation and moment of the mass.
 Statical moment, the product of a force into its leverage; the same as moment of a force with respect to a point, line, etc.
 Virtual moment. See under Virtual.
 Syn: -- Instant; twinkling; consequence; weight; force; value; consideration; signification; avail.
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 Vir·tu·al a.
 1. Having the power of acting or of invisible efficacy without the agency of the material or sensible part; potential; energizing.
    Heat and cold have a virtual transition, without communication of substance.   --Bacon.
 Every kind that lives,
 Fomented by his virtual power, and warmed.   --Milton.
 2. Being in essence or effect, not in fact; as, the virtual presence of a man in his agent or substitute.
    A thing has a virtual existence when it has all the conditions necessary to its actual existence.   --Fleming.
    To mask by slight differences in the manners a virtual identity in the substance.   --De Quincey.
 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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