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Energy Losses in Commercial Hammers. 



Edwin Morrison and Robert L. Petry — Earlham College. 



It is a well-known principle of mechanics that, in case a moving- 

 object impinges against another object, that the total momentum before 

 impact is equal to the total momentum after impact. In other words, 

 "That momentum is conserved in all impacts, be it between elastic or 

 inelastic objects." This law does not permit us to infer, however, that 

 there are no energy losses in impacts. In fact the kinetic energy is 

 always less after impacts than before impacts of two impinging objects. 

 By testing this out by ordinary laboratory methods we find these energy 

 losses to vary from as high as eighty per cent in case of inelastic impacts 

 to as low as two per cent in elastic impacts. 



In teaching this subject I have for a number of years attempted 

 to illustrate and fasten these principles in the mind of the student by 

 such questions as the following: Suppose a carpenter is employing a 

 number of men in a mechanical process, such as the driving of nails 

 with a hammer, would it be of importance for him to look into the 

 grade of hammers used? Or again: Suppose a railroad company is 

 retracking its line and it is necessary to drive thousands of spikes, does 

 it matter whether the sledge hammers used are made of cast iron or a 

 high grade of steel? 



It so happened that my present class inquired as to whether it 

 would be possible to try these conditions out in an experimental way. 

 After a moment's reflection I informed them that it would be a very 

 simple matter to make tests by substituting a hammer for one of the 

 steel spheres in our impact machine. This has been done in the case 

 of four hammers with considerable care. 



The apparatus used was similar to that employed in Experiment 6, 

 page 62, in Millikan's Mechanics, Molecular Physics, and Heat. One of 

 the steel spheres was removed and the hammer to be tested was sub- 

 stituted in its place as shown in Fig. 1. In order to support the dif- 

 ferent hammers as nearly as possible under the same conditions, a frame 

 was suspended by four adjustable cords, to which the hammers could be 



