. A text book of physics, for the use of students of science and engineering . handles. For thepurposes of experiment, the handleshave been removed and a wheel Dsubstituted. D is rotated by meansof a cord and weights placed in ascale-pan at P, and drives the barrelby medium of the toothed wheels Cand B. Fig. 211.—A small lifting crab. -n, v j , ,1 • i- Energy is supplied to this machine by means of a comparatively small force P acting through a large distance, and is delivered by the machine in the form of the work done in overcoming a large force W through a small distance. If no energy were
. A text book of physics, for the use of students of science and engineering . handles. For thepurposes of experiment, the handleshave been removed and a wheel Dsubstituted. D is rotated by meansof a cord and weights placed in ascale-pan at P, and drives the barrelby medium of the toothed wheels Cand B. Fig. 211.—A small lifting crab. -n, v j , ,1 • i- Energy is supplied to this machine by means of a comparatively small force P acting through a large distance, and is delivered by the machine in the form of the work done in overcoming a large force W through a small distance. If no energy were wasted in a machine, it would follow, from theconservation of energy, that the energy supplied must be equal totli«> energy delivered by the machine. Thus, referring to Fig. 211,Work done by P = Work done on W. Tins statemenl Is generally referred to as the principle of work,and requires modification for actual machines, in which there isalways some energy wasted. Actually, the energy supplied is equalto the sum of the energy delivered by the machine and the energy. MACHINES 185 wasted. The investigation of frictional resistances in the variouskinds of lubricated rubbing surfaces of machines is beyond thescope of this book. Usually, however, it is the determination of thetotal waste of energy in the machine which is of importance, andexperiments having this object are performed easily in the case ofsimple machines used for raising loads. Some definitions regarding machines.—In Fig. 212 is shown anoutline diagram of the crab illustrated in Fig. 211. Let W be raised through a height h while P descendsthrough a height H, H and h being inthe same units. The velocity ratio of themachine is defined as the ratio of the dis-tance moved by P to the distance movedby W in the same time, or
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Keywords: ., bookcentury1900, bookdecade1910, bookpublishe, booksubjectphysics
