POWER IN MOTION Horse Power, Wheel Gearing, Dribing Bands, LOCKWOOD & CO., 7, STATIONERS' HALL COURT, PREFACE. In this short treatise the general laws that govern power in motion are exhibited in simple form, to meet the known wants of practical men engaged in engineering works that require the employment of horses, hoists, block and tackle, wheel gearing, and long and short driving bands, of wire rope or of leather. The aim is, so to explain the essential principles, that the value of means proposed for the performance of work, under the varied circumstances of common practice, may be easily determined. Common arithmetic alone is used in working out the questions, except in the case of driving bands, when, for the extraction of certain values, common logarithms are employed necessarily, but in so simple a manner that no difficulty need be felt, even by those unaccustomed to the use of logarithms. In treating questions of angular force a table of natural sines, &c., is necessary, where the value is decided by the angle; but the simple method of computing by the tabular values of the angle has been so circumstantially explained, and exhibited so plainly in the illustrations, that no difficulty need occur here either. GATESHEAD, April, 1871. POWER IN MOTION. SECTION I. 1. Power, and work done, stand relatively to each other as cause and effect. Pressure is power in an active state. Resistance, without which pressure cannot exist, is power in an inert state. When the resistance equals the pressure, there is no work done, because of the balance between the forces. When the resistance is less than the pressure, the resisting body is pressed out of its place, and the extent of its motion multiplied by its resistance, gives the measure of the work done by the moving power. 2. As it has been found convenient to adopt a unit of length, termed 1 foot, for measuring distance, and a unit of weight, termed 1 lb., for measuring gravity, and a unit of time, termed 1 minute, for measuring time; so it has been found necessary in measuring forces, to adopt what is termed a unit of work, which is performed whenever a pressure of 1 lb. is exerted through the space of 1 foot in any direction; that is, either in lifting or in pushing. We must distinguish, however, between mere deadweight suspended, and the same when rolling or sliding: thus, the pressure exerted through the space of 1 foot will, in the case of sheer lifting, be simply not less than the weight lifted; whereas in a case of pushing or pulling, B |
