MECHANICAL POWERS. This name is given to certain simple machines or engines, either of which is occasionally used by itself in moving bodies or raising weights, or any of which are combined together in the formation of the complex constructions which are em ployed in manufactures and the arts.
The several machines to which the name of mechanical powers is applied are the LEVEE, the WHEEL AND AXLE, the INCLINED PLANE, the WEDGE, the SCREW, and the FUNICULAR MACHINE.
The object proposed in every machine is to transmit a force from the point at which it is immediately applied to that at which some resistance is to be overcome or some opera tion to be performed ; and, in the transmis sion, the intensity of the motive power is to be increased so that effects may be produced which could not be accomplished by that power alone. The increase of the power is obtained by causing part of the resistance which is to be overcome to rest on the machine or on the fixed points which serve for its sup port, so that only the part which remains is opposed to the motive force. Thus a heavy
body may be raised to a certain height from the ground by means of an inclined plane, on which part of the weight is destroyed by the reaction of the plane.
This manner of overcoming a resistance will serve to illustrate the fact that in every application of a mechanical contrivance to overcome a resistance, as much advantage is lost in respect of time or space as is gained in respect of power. For it is evident that, in order to raise the object vertically through a space equal to the height of the plane, it would be necessary to move it over a space equal to the length of the plane: that is, through a space which bears the same ratio to the vertical height as the weight of the object bears to the power required to move it np the plane.
All the familiar tools, implements, instru ments, machines, and engines, exhibit the operation of some one or more of the mecha nical powers.