| 释义 |
velocity|vɪˈlɒsɪtɪ|
Also 6 Sc. velocite, 6–7 velocitie.
[ad. F. vélocité (14th cent.; = It. velocità, Sp. velocidad, Pg. -idade) or L. vēlōcitāt-, vēlōcitās, f. vēlōci-, vēlox swift, rapid: see -ity.]
1. a. Rapidity or celerity of motion; swiftness, speed.
c1550Rolland Crt. Venus ii. 672 Thay bad him pas with all velocite To the Gracis. 1555Eden Decades (Arb.) 220 This byrde..is of such velocitie and swyftnes in flying that [etc.]. 1607Topsell Four-f. Beasts 115 The Lybian Roes..(saith hee) are of an admirable velocity or swiftnes. 1646Sir T. Browne Pseud. Ep. 235 Dolphins..Being the Hyeroglyphick of celerity,..men best expressed their velocity by incurvity, and under some figure of a bowe. 1665Glanvill Scepsis Sci. xi. 61 The supposed motion will be near a thousand miles an hour under the Equinoctional line; yet it will seem to have no Velocity to the sense. 1704Fuller Med. Gymn. (1711) 14 His Blood flows with its due Velocity. 1789Mrs. Piozzi Journ. France II. 370 Black heaths, and wild uncultivated plains, over which the unresisted wind sweeps with a velocity I never yet was witness to. 1802Bingley Anim. Biog. (1805) III. 74 Some of the species..are enabled to spring with great force and velocity on their prey. 1849Macaulay Hist. Eng. iii. I. 379 The flying coaches are extolled as far superior to any similar vehicles ever known in the world. Their velocity is the subject of special commendation.
b. spec. Relative rapidity; rate of motion.
1656tr. Hobbes' Elem. Philos. (1839) 113 Motion, in as much as a certain length may in a certain time be transmitted by it, is called Velocity or swiftness: &c. 1715tr. Gregory's Astron. (1726) I. 91 The Velocity in A is to the Velocity in P, as SN to SH. But as the Velocities in A and P, so are the Spaces run in the same time, by the Bodies. 1743W. Emerson Fluxions v, It is the general Practice in Mechanics, to measure the Velocity of a Body by the Space uniformly described in given Time. c1790J. Imison Sch. Arts I. 1 Mechanics is a science which treats of the forces, motions, velocities, and in general, of the actions of bodies upon one another. 1813Bakewell Introd. Geol. Pref. (1815) 16 In mechanics, the important question of the ratio between the velocity and momentum is still undecided. 1857Livingstone Trav. xvi. 284 note, A declivity of three inches per mile gives a velocity in a smooth straight channel of three miles an hour. 1880Haughton Phys. Geogr. iii. 137 It has..a velocity of upwards of three knots per hour.
c. In scientific use, speed together with the direction of travel, as a vector quantity.
1847Proc. R. Irish Acad. III. 345 We may always imagine a succession of straight lines, or vectors, to be drawn from some one point, as from a common origin, in such a manner as to represent, by their directions and lengths, the varying directions and degrees (or quantities) of the velocity of the moving point. 1873J. C. Maxwell Treat. Electr. & Magn. I. 9 The velocity of a body, its momentum,..an electric current,..are instances of vector quantities. 1883Encycl. Brit. XV. 680/1 We are concerned only with what we may call the ‘speed’ of the motion. (We purposely avoid the use of the term ‘velocity’ here, because it properly includes direction as well as speed.) 1963A. F. Abbott Ordinary Level Physics v. 50 In ordinary conversation the word ‘velocity’ is often used in place of speed. In science, however, it is important to distinguish between these two terms.
2. a. Rapidity (absolute or relative) of operation or action; quickness.
a1674Clarendon Surv. Leviath. (1676) 18 Mr. Hobbes..was with the velocity of a thought..able to decipher that impertinent Question. 1743W. Emerson Fluxions 2 He will find some to increase faster, others slower; and consequently that there are comparative Velocities (or Fluxions) of Increase during their Generation. 1794Hutton Philos. Light, etc. 198 Neither the quantity of the fire, nor the velocity of its propagation. 1817Jas. Mill Brit. India II. v. v. 479 Colonel Brathwaite was instructed to anticipate resistance by velocity of completion. 1858Froude Hist. Eng. IV. 481 The velocity with which the English world was swept into the New Era. 1871B. Stewart Heat (ed. 2) §228 The rate at which it loses temperature or the velocity of cooling.
b. Econ. The rate at which notes and coins change hands; the rate of spending in an economy.
1909I. Fisher in Jrnl. R. Statistical Soc. LXXII. 618 When we know statistically the velocity of circulation of money we shall be in a position to study inductively the ‘quality theory’ of money. 1911― Purchasing Power of Money ii. 17 Velocity of circulation, or rapidity of turnover, is simply the quotient obtained by dividing the total money payments for goods in the course of a year by the average amount of money in circulation by which these payments are effected. 1930J. M. Keynes Treat. Money II. xxiv. 20 The expression ‘velocity (or rapidity) of circulation’ first came into use before the development of the cheque system... The ‘velocity’ measured the average frequency with which a loan (or a bank-note) changed hands. 1957Economist 19 Oct. 209/1 The note issue is a good indicator because the velocity of notes, unlike that of deposits, is fairly steady. 1982Chase Economic Observer Jan.–Feb. 3/1 Velocity, the rate of turnover of money, is typically measured as the ratio of GNP to the narrowly defined money stock.
3. attrib. and Comb., as velocity-measurer, velocity ratio; velocity head [head n. 17], the velocity pressure of a fluid expressed in terms of the height from which the fluid would have to fall to attain the velocity exerting this pressure; velocity microphone, a microphone whose diaphragm is freely exposed to the air on both sides and so responds to the particle velocity within a sound wave rather than its pressure; velocity potential [tr. G. geschwindigkeitspotential (H. von Helmholtz 1858, in Jrnl. für die reine u. angewandte Math. LV. 25)], a scalar function of position such that its space derivatives at any point are the components of the fluid velocity at that point; velocity pressure, that part of the total pressure exerted by a fluid which is due to the velocity it possesses.
[1881Encycl. Brit. XII. 462/2, v2/2g may be termed the head due to the velocity v.] 1884A. Daniell Text Bk. Princ. Physics xi. 276 We may say that the velocity-head and the pressure-head are together equal to the total head. 1937O'Brien & Hickox Appl. Fluid Mech. ix. 271 The true velocity head to be used in Bernoulli's equation is the average kinetic energy per unit weight of water flowing. 1979A. L. Lydersen Fluid Flow & Heat Transfer i. 5 (caption) Pressure head (p/ρg) and velocity head (V2/2g) for frictionless flow from point 1 to point 2.
1849–50Weale Dict. Terms s.v. Velocimeter, Such a velocity-measurer was constructed by Breguet, of Paris.
1931H. F. Olson in Jrnl. Soc. Motion Picture Engineers XVI. 695 The ribbon microphone..can therefore very appropriately be termed a ‘velocity microphone’. 1951A. Sheingold Fund. Radio Communications xiii. 281 Velocity microphones may be designed to be unidirectional in their response. 1978V. Capel Microphones in Action ii. 19 The polar diagram of a velocity microphone is different from anything we have discussed so far.
1867P. G. Tait tr. Helmholtz in Phil. Mag. XXXIII. 485 In integrating the hydrodynamical equations, the assumption has been made that the components of the velocity of each element of the fluid in three directions at right angles to each other are the differential coefficients, with reference to the coordinates, of a definite function which we shall call the velocity-potential. 1878W. K. Clifford Dynamic iii. 203 The circulation along any path from o to p..is called the velocity-potential at p. 1882Minchin Unipl. Kinemat. 160 If..the velocity potential has at each point of the curve an assigned value. 1907F. W. Lanchester Aerodynamics iii. 91 Fluid in irrotational motion has a velocity potential. 1937[see stream function s.v. stream n. 9 c]. 1980Bober & Kenyon Fluid Mech. ix. 417 The velocity potential, ϕ, or the stream function, Ψ, are often introduced into fluid-flow problems because they frequently reduce the difficulty in obtaining a solution to a particular problem.
1904Proc. Inst. Mech. Engin. Feb. 298 They used dry, clean air, and therefore it was possible to keep the Pitot tube extremely small, and to measure the static pressure in the close neighbourhood of the point at which the velocity pressure was measured. 1959N. C. Harris Mod. Air Conditioning xv. 293 Velocity pressure is best measured by a Pitot tube combined with a draft gage which reads in inches of water. 1969Oceanology IX. 585 The instrument is based on the measurement of the velocity pressure created by the wind.
1887D. A. Low Machine Draw. (1892) 36 Velocity Ratio in Belt Gearing. |