Volume 1
A course of lectures on natural philosophy and the mechanical arts / by Thomas Young.
- Thomas Young
- Date:
- 1845
Licence: Public Domain Mark
Credit: A course of lectures on natural philosophy and the mechanical arts / by Thomas Young. Source: Wellcome Collection.
Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.
91/670 page 57
![Acta Petrop. iii. II. 106. Belidor, Ingenieur Fran9ais. Fuss, Nova Acta Pe- trop. 1788, vi. 197. Nicholson’s .Tournal, iv. 443. Virtual Velocities.—Galileo, Dial. 1592. De Cans, les Raisons des Forces Mou- vantes, Antwerp. Bp. Wilkins’s Mathematical Magic, 1648. J. Bernoulli, in Va- rignon’s Mec. 1717. D’Alembert, Hist, et Mem. 1769, p. 278. Lagrange on a Property of the Centre of Gravity, Ac. Berl. 1783, p. 290. Do. on Virtual Velo- cities, Journal Polytechnique, ii. V. 115. Fossombroni sul Principio delle Velocita Virtual!, 4to, Flor. 1796. Essay on Virtual Velocities, Journal de Physique, xlviii. 210. Fourrier and Prony on Do. Journal Polytechnique, ii. V. 20,191. Buquoy, Analytische Bestimmung des Gesetzes der Virtuellen Geschwindigkeiten, Leips. 1812. Do. Weitere Entwickerung, do. 1814. Do. E.vposition d’un Nouveau Principe General de Dynamique, dont le Principe des v. v. n’est q’un cas particulier, 4to, Paris, 1815. Pagani, Mem, de I’Acad. de Bruxelles, 1825, iii. Gauss in Crelle’s Journal, Band 4. Mobius Lehrbuch der Statik, Leipz. 1837. LECTURE VIII. ON COLLISION. Having inquired into the laws and properties of the motions and rest of single bodies under the operation of one or more forces, and into the equi- librium of these forces in different circumstances, we are next to examine some simple cases of the motions of various moveable bodies acting recipro- cally on each other. In all problems of this kind, it is of importance to recollect the general principle already laid dowm respecting the centre of inertia [gi-avity] that its place is not affected by any reciprocal or mutual action of the bodies constituting the system. Whenever two bodies act on each other so as to change the direction of their relative motions, by means of any forces which preserve their activity undiminished at equal distances on every side, the relative veloci- ties with wliich the bodies approach to or recede from each other, will always be equal at equal distances. For example, the velocity of a comet, when it passes near the earth in its descent towards the sun, is the same as its velocity of ascent in its return, although at different distances its velocity has undergone considerable changes. In this case, the force acts continually, and attracts the bodies towards each other ; but the force concerned in collision, when a body strikes or impels another, acts only during the time of more or less intimate contact, and tends to separate the bodies from each other. When this force exerts itself as powerfully in causing the bodies to separate as in destroying the velocity with which they meet each other, the bodies are called perfectly elastic ; when the bodies meet each other without a re-action of this kind, they are called more or less inelastic. Ivory, metals, and elastic gum, are highly, and almost perfectly elastic : clay, wax mixed with a little oil, and other soft bodies, are almost inelastic : and the effects of inelastic bodies may be imitated by elastic ones, if we cause them to unite or adhere after an impulse, so as to destroy the effect of the i-epulsive force which tends to separate them.](https://iiif.wellcomecollection.org/image/b21301840_0001_0091.jp2/full/800%2C/0/default.jpg)
