ISO

FRICTION OK C A III! IAU K.S

power in itself to change that velocity, anil itis not supposed to be effected by any othermechanical force whatever. — Suppose, now,instead of the body being - perfectly free fromfriction, that it is continually opposed by acertain determinate force or pressure, which isalways acting with the same intensity, inretarding the progressive motion of the body ;then the body, instead of continuing in a stateof uniform motion, will, by the constant retar-dation of this force, be soon brought to a stateof rest. Suppose, however, when it is in astate of uniform velocity, and subjected to theaction of this retarding force, we apply, orcause a force continually to act upon the body,urging it forward with the same intensity ofpressure that the retarding force, or friction ofthe body, opposes to its progressive motion—then the body will still continue to move on ina state of uniform velocity, and with the samevelocity given to it. When, therefore, a car-riage is placed upon a Hail-road, and a con-tinual pressure is exerted upon it, to urge itforward, (as the action of the men through themedium of the rope of the dynamometer,)it is found that, with whatever velocity itis moved, supposing the moving force toproceed with the same velocity, the pres-sure required to keep it in a state of uniform