A. S. Kimball— Sliding Friction on an Inclined Plane. 181 



Art. yi-Kll.— Sliding Friction . 

 Kimball, Professor of Phy 

 Institute of Industrial Scienct 



The following investigation was undertaken with a desire to 

 demonstrate, if possible, by a laboratory experiment, that the 

 law which affirms that the coefficient of sliding friction is con- 

 stant for all velocities is not strictly true. 



Our results seem to establish the point, at least in the case 

 of bodies sliding down an inclined plane. I am aware that the 

 truth of this law has been questioned; indeed the opinion of 



made at the slide of Alpnach, that it would appear that friction 

 is neither proportioned to the pressure nor independent of the 

 velocity. Later observations made at the launching of the 

 Raritan and the Princeton (Jour. Frank. Inst., 3d, VII, 108) 

 showed that the coefficient of friction just before the vessel left 

 the ways was much less than during the first five seconds of its 

 motion. More recent still are the experiments of M. Bochet 

 (Comptes Rendus, April 26, 1858,) upon the friction of railway 

 carriages and brakes, which point to the same conclusion ; in- 

 deed the author goes so far as to give the form of the function 

 which expresses the variation of the coefficient of friction with 

 the velocity, and gives approximate values to its constants for 

 the case of railway trains. His formula is copied by Weisbach 

 with a caution. 



Opposed to these views are the careful experiments of 

 Coulomb and Morin, upon which 

 books are founded. 



The apparatus used in our experiments was 

 capable of giving very sharp and reliable i 

 pme plank Wxl2"x2" was firmly placed a 

 with the horizon and supported throughout by stout oeams. 

 Upon this plank was a weight box with pine runners, having a 

 bearing surface of 24 square inches. The cover of the box was 

 about six feet in length, and upon it were placed slips of smoked 

 glass. Firmly fixed above the glass, to an independent sup- 

 port, was a verified tuning fork of 435 complete vibrations per 

 second, carrying a style which lightly touched the glass surfiace 

 beneath it. The weight box was supported in position at the 

 upper end of the inclined plane by a cord fastened to a screw 

 which served to give the box a very slow upward motion. At 

 the proper time the screw was turned, the fork vibrated, the 

 cord cut or burned off, and the box allowed to slide to the bot- 

 toin of the plane. The style of the fork at the same time 



