FORCE AND NOTION. 



43 



two clay balls of equal mass by strings of equal lengths 



so that they will just touch each other. If one be drawn 



aside and let fall against 



the other, both will move 



forward, but only half as 



far as the first would had 



it met no resistance. The 



gain of momentum by the 



second is due to the action 



of the first. It is equal 



to the loss of momentum 



by the first, which loss is 



due to the reaction of the 



second. 



95. Reaction in 

 Elastic Bodies. If 



two ivory balls, which are 

 elastic, be similarly placed, 

 and the experiment re- 

 peated, it will be found FIG. 16. 

 that the first ball will give 



the whole of its motion to the second and remain still 

 after striking, while the second will swing as far as the 

 first would have done if it had met no resistance. In this 

 case, as in the former, it will be seen that the first ball 

 loses just as much momentum as the second gains. 



96. Reflected Motion. Reflected motion is 

 the motion produced by the reaction of a surface 

 when struck by a body, either the surface, or the 

 body, or both being elastic. 



A ball rebounding from the wall of a house, or from the 



