50 APPARATUS FOR DEMONSTRATING LAWS OF MOTION. 



weight suspended by a cord, and carrying below a very 

 small weight attached to it by a silk thread, which 



passes through a short glass tube. 

 The small weight rests on a hard 

 support, when the pendulum is 

 not in motion ; but at each vibn 

 tion it is raised and again low- 

 ered upon the support with 

 distinctly audible sound. 



The two weights of 70 gr each 

 being suspended by the cord 

 which passes over the wheel, the 

 whole is in equilibrium, and 

 rest. The force of gravity acl 

 in this case equally upon botl 

 sides, and the two equal but 



opposite forces produce no effect whatever, just as 

 if they did not act at all. If the cord is arranged in 

 such a manner that one weight is at the top and the 

 other at the bottom of the scale, and the lower weight 

 be gently set in motion upwards by a slight push of the 

 finger, the motion ought uniformly to continue until 

 this weight has ascended to the top, while simul- 

 taneously the other has descended ; this would indeed 

 happen if the weights and the wheel could solely obey 

 their inertia, but the unavoidable friction renders the 

 motion gradually slower and brings the whole finall} 7 

 to rest. The resistance of the air to this slow mo- 

 tion is so small that it may be neglected, nor need the 

 small weight of the cord be taken into consideration. Tc 

 counteract the disturbing influence of friction, a smal 

 weight of the form ?, fig. 43, is used. It is placec 



