EXERCISE 67 



CAN ONE KIND OF ENERGY BE CHANGED INTO ANOTHER KIND? 



Materials. Some wire nails or small pieces of iron wire ; a piece of iron or a stone to serve as an 

 anvil ; a hammer ; some copper wire ; a rubber or ebony rod ; a piece of flannel cloth. 



Directions. By holding a nail or wire in the hands, note its temperature. Place the nail or wire 

 on an anvil or heavy piece of iron and strike it several blows with a hammer. Now pick up the nail 

 or wire and note its temperature. How do you account for the change in temperature ? 



Bend a copper or iron wire several times and then feel the part where the bending took place. 

 Explain your result. 



Write your answer to the above question, giving the results of the experiments and stating your 

 conclusion. 



Additional problems. Rub a rod of rubber or ebony, or a fountain pen, with a piece of flannel, and then 

 bring it to your ear. What kind of energy was present on the rod ? How did it come to be there ? 

 Rub the rod again and bring it near some very small scraps of paper. What is the result? 



Why does an ungreased wagon or carriage axle become hot when used ? 



When sawing wood, does the saw become heated ? Does the wood become heated ? Why ? 



How did uncivilized tribes of men start their fires ? What principle is involved in this method of 

 starting fires ? Can you start a fire in the same way ? 



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