On the Motion of Bodies affected by Frktlon. 3* 



the friction docs not increase in so great a ratio as tlie weight : 

 \vc iiiav therefore conchide tjnat the friction of a body doc.-; 

 rial continue the same when it has different surfaces applied 

 to the plane oti which it moves, but that tlie smallest surface 

 u ill hare the least friction. 



7. Having thus estahhshed, tVoni the most decisive ex- 

 periments, all that I proposed relative to friction, I think 

 it proper, before I conckide, to give tlie result of my ex- 

 amination into the nature of the experiments which have 

 been made by others ; which were repealed in order to see 

 how i'ar they were conclusive in respect to the prmciples 

 which have been deduced from them. The experiments 

 which have been made by all the authors that I have seen 

 have been thus instituted. — To find what moving force would 

 just put a body at rest in motion : and they concluded from 

 thence, that the accelerative force was then equal to the 

 friction ; but it is manifest that any force which will put 

 a bodv in motion must be greater than the forc,e which op- 

 poses its motion, otherwise it could not overcome it ; and 

 hence, if there were no other objection than this, it is evi- 

 dent that the friction could not be very accurately obtained ; 

 but there is another objection which totally destroys the ex- 

 periment 9o far as it tends to show the quantity of friction, 

 which is the strong cohesion of the body to the plane when 

 it lies at rest ; and this is confirmed by the following ex- 

 periments. 1st, A body of 12l oz. was laid upon an hori- 

 zontal plane, and then loaded with a weight of 8 lb. and 

 such a moving force was applied as would, when the body 

 was just put in motion, continue that motion without any 

 acceleration, in which case the friction must be just equal 

 to the accelerative force. The body was then stopped ; when 

 it appeared that the same moving force which had kept the 

 bodv in motion before would not put it in motion, and it was 

 found necessary to take off 4^ oz. from the bodv before the 

 san)e inovin<>; force would put it in motion : it appears, 

 therefore, that this bodv, when laid upon the plane at rest, 

 acquired a.verv strong cohesion to it. 2dly, A bodv whose 

 w eight V. as Hi oz. was laid at rest iq)on the horizontal plane, 

 and it was I'ound that a moving force of 6 oz. would just 

 put it in motion; but that a mo\ing force of 4 oz. would, 

 when it was just put in motion, continue that motion w ith- 

 oiit any acceleration, and therefore the accelerative force 

 iiiusi then have been ctpial to the friction, and not when 

 tlie nioving force of 6 oz. was applied. 



I'xom these experiments iheretore it appears, how very 

 D 4 cun- 



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