338 



Mr Vincent, Experiments on Impact. 



The preceding experiments with the steel ball and indiarubber 

 bung tend to show that e in the other cases decreased uniformly 

 as the velocity of approach increased and to indicate that the 

 results are not very much affected by the resistance of the air. 

 There are practical difficulties in the accurate determination of e 

 for large and for small velocities of approach, and it would be 

 fallacious to lay stress on the results of wide extrapolation of such 

 curves as are given in the figures. Yet the experiments indicate 

 the possibility and even the probability of the existence in the 

 above cases of a maximum value for e which occurs when the 

 velocity of approach is vanishingly small and which is considerably 

 less than unity. Also the existence of a maximum velocity of 

 rebound is indicated. 



Experiments with Lead. 



In order to determine the circumstances of impact in which 

 one or both of the bodies suffer permanent deformation it seemed 

 desirable to find the relation between the deformation produced 

 and the velocity. 



In Fig. 6 we have the results obtained by dropping a " hard," 

 highly polished steel ball, mass 67 grammes, on to a slab of lead 1 . 

 The diameter of the ball was 2 - 54 cm. and the slab of lead was 

 5 cm. thick with a surface of 15 x 20 sq. cms. 



Vel. of Approach in cms. a sec. 

 Fig. 6. Steel Ball (2-54 cms. diameter) falling on lead. 



The surface of the lead blocks used in this and succeeding 

 experiments was prepared by planing with a carpenter's plane. 

 This tool when set so as to cut a very thin shaving will plane lead 

 readily, if oil is used freely as a lubricant. The surface thus 

 prepared has a remarkably beautiful appearance. The crystals 

 composing it are seen in reflected light and if the lead has been 

 " chilled " the sections of the crystals are on an average about a 



1 The lead Avas commercial plumbers' lead. 



