Physics for students of medicine.

  • Daniell, Alfred, 1853-1937.
Date:
1909
Catalogue details

Licence: In copyright

Credit: Physics for students of medicine. Source: Wellcome Collection.

Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.

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    it; and if any contrivance he so made as to enable us to get a given amount of Work done by a longer aud less direct path, we lind it easier to do that work, for tlie force along the longer path is less in jn'oportion to the increased length of path. In uu Inclined Plane, suppose a lieavy body is pushed up from A to B, wliere Al> = t51 cm., so as to make it gain vertical height equal to CB = 11 em. ; the Work done (apart from friction) = Weight of the body X 11 em. But this has been effected by exert- ing a force less tlian the Weight, through a greater distance AB ; the Force exerted up the slope is therefore thnes the Weight of the body lifted: in the instance supposed, it is to the Weight of the body lifted as 11:61. ,^ , • .1 If the force applied be kejit parallel to AC, on reachmg the top the liorizontal force will have been kept up tlirough a horizontal distance AC ( = 60 cm.); the force exerted hori- zontally is thoi'efore smaller than the Weight of the body, ui the ratio 11 :60. , , , , , If the inclined plane be pushed under the heavy body, a movement of the wedge horizontally through, say 6 cm. would correspond to an upward movement of the heavy body througli 1-1 cm • and the Force necessary to accomplish this would be U the Weirdit of the heavy body. This is the principle of the wedge In practice more work than this would have to be done on account of friction ; but friction is useful in respect that it prevents the wedge from .slipping back. The thread of a screw corresponds, as may be seen in any specimen, to a narrow inclined plane wrapped round a cylinder In a copying-press, say of arms 12 inches each, screw 1. mcli tliick with threads i inch apart, when either hand moves throucrh 1 inch the point of the screw moves inch : hence the Force which can be exerted by such a screw-press is _b4b times that which can be directly applied by the hands. 1 his is applied in table-clips, iu presses for separating muscle juice from muscle, in clipping the points of forceps, etc. The Screw is also used as a means of measuring small thicknesses. For example, in measming the thickness ot a microscopic cover-glass, the cover-glass is g':««P''\'\V ' ^ separable steel jaws whose mutual position is contro led bj a se w If flic ^^'r^v I'ave 20 threads to the inch each turn ot the screw will separate the laws through „V '^l' ; ''^^ ^^'^