MEGHAN I C 



TREATISE I. 



ON THE MECHANICAL AGENTS OR FIRST 



CHAPTER I. Introduction. 



(1.) WHATEVER communicates or tends 

 to communicate motion to a body, is 

 called a. force. The object of MECHA- 

 NICS, in the most extended sense of that 

 term, is the investigation of the effects 

 of forces on bodies. 



If a body which is absolutely at rest 

 be submitted to the action of two or 

 more forces, one of two effects must 

 ensue ; either the body must continue in 

 its state of rest, or it must commence to 

 move in some determinate direction, 

 and with some determinate force. If 

 the body continue at rest, it necessarily 

 follows, that the forces which act upon 

 it are so related as to their directions 

 and intensities, that they neutralise each 

 other, or mutually destroy each other's 

 effects. Under such circumstances, the 

 body is said to be in a state of equili- 

 brium* and we also commonly apply 

 the same term equilibrium to the forces 

 \vhich act upon the body. 



It is, therefore, a Very important 

 problem, or rather class of problems, to 

 assign in every particular case that rela- 

 tion between the intensities and direc- 

 tions of the forces acting upon a body 

 under given circumstances, which will 

 keep the body in a state of equilibrium. 

 By the solution of such a problem, we 

 shall always be able to predict whether 

 a body urged by given forces shall re- 

 ceive any motion or not. 



If the forces which act upon the body 

 be not so related" as to neutralise each 

 other's effects, motion must ensue, and 

 the body will be urged with some deter- 

 minate force in some determinate direc- 

 tion. To assign the force with which 

 the body will thus be moved, and the 

 direction of its motion, the intensities 

 and directions of the forces impressed 

 on the body being given, is another im- 

 portant class of problems, and of a na- 

 ture altogether distinct from the former. 



(2.) These considerations suggest the 



Equilibrium is originally a Latin word signifying 

 , the forces, as it were, balancing each other. 



division of the science into two parts. In 

 the first, which is called statics* bodies 

 are considered as submitted to the in- 

 fluence of forces which are in equili- 

 brium. 



(3.) In the second part, which is called 

 dynamics,^ bodies are considered as 

 submitted to the action of forces which 

 are not in equilibrium. In the former, 

 therefore, bodies are considered at rest, 

 and in the latter as in motion. 



(4.) Although this be unquestionably 

 the most philosophical division of the 

 subject, and that which should be adopt- 

 ed in a treatise designed for the use of 

 certain classes of students ; yet, consi- 

 dering the objects which we have in view 

 in the present series of works, and the 

 persons for whose instruction they are 

 intended, we think it expedient to pur- 

 sue a different course, and do not hesi- 

 tate to sacrifice system to utility. 



In all the various changes which the 

 raw productions of nature must undergo 

 in order to adapt them to supply the 

 wants of civilized life, motion is the'prin- 

 cipal agent. The wool which is shorn 

 from the sheep, requires a rotatory mo- 

 tion to form it into threads. These 

 threads must be submitted to a variety 

 of other motions, in order to produce 

 that arrangement which gives them the 

 form of cloth ; and cloth when woven 

 must pass through many other pro- 

 cesses, in all of which motion is the 

 chief agent, before it is prepared for use. 

 To obtain these motions, we avail our- 

 selves of the forces which we find actu- 

 ally existing in nature, such as the 

 foiling of water, the force of wind, the 

 strength of animals, and numerous 

 others. As, however, the forces and 

 motions which are required for the 

 various manufactures, are generally dif- 

 ferent in many respects from those forces 

 with which nature has supplied us, it is 



From a Greek word 

 standing still. 



t From the Greek wor 

 ing force. 



statos, sijnifying 

 dunamit, signify. 

 B 



