356 Mr Vincent, Experiments on Impact. 



out in Fig. 16. It will be seen that paraffin although more easily 

 deformed than lead has always a higher coefficient of restitution. 



The experiments were performed on massive blocks of the 

 materials. 



Summary of Results. 



In the case of indiarubber balls impinging on a non-deformable 

 plane and also for a non-deformable sphere impinging on a block 

 of indiarubber, the equation 



e = e — mu 



gives the value of e for any velocity of approach u, e and m being 

 positive and constant. 



For a steel ball impinging on the plane surface of a lead, 

 paraffin, brass, or cast-iron block e rises rapidly when the velocity 

 of approach becomes small. For large velocities of approach e is 

 given approximately by the same formula as above. 



Hammering the surface of lead increases e whether the lead 

 be a " chilled " or a slowly cooled casting. 



The dents produced by the impact of non-deformable spheres 

 on plane surfaces of lead, paraffin, brass, and cast-iron obey the 

 following simple rules when the velocity of impact is not great : 



(1) The square of the diameter of the dent is proportional to 

 the velocity of impact. 



(2) For spheres of the same material impinging with the 

 same velocity, the diameter of the dent is proportional to the 

 diameter of the sphere. 



From which it follows when e is small, i.e. for lead and paraffin, 

 that : 



(3) The time taken by any one sphere to produce a dent is 

 independent of the velocity of impact. 



(4) The pressure (p) between the surfaces in contact is con- 

 stant during this time. The value of p for different specimens 

 of lead varies from 6 x 10 8 to 13 x 10 8 dynes per sq. cm. While 

 for " soft " paraffin it is about 1 x 10 8 dynes per sq. cm. 



These results may be grouped together when the velocity of 

 impact and the radius of the sphere both change by the rule 

 that : 



