CHAPTER IX 

 HEAT AND EXPANSION 



100. Generation and Movement of Heat. If wo file a 

 soft iron nail for a moment and then feel the file surface, 

 we find that it is warm or hot ; that is, the surface of the file 

 is warmer than the body. Another way of expressing the 

 same idea is to say that the temperature of the surface of the 

 file is higher than that of the body. There is then a transfer 

 of heat from the warmer body to the colder body, until both 

 are equally warm. Then both bodies are said to have the 

 same temperature. A hot frying pan when plunged into 

 a bucket of water gives off heat to the water, until the 

 temperatures of the water and the frying pan become equal. 

 Temperature is a measure of the tendency of a body to give up 

 its heat to other bodies. 



The surface of the file becomes warm or hot because of 

 friction. The same effect is produced on the surface of a 

 saw in sawing wood, in rubbing a metal surface on cloth, in 

 the bearings of moving car-wheels, etc. Heat is generated 

 also when a piece of lead or other metal is hammered and 

 when a rifle bullet strikes a wall. This heat is caused by 

 percussion. 



Heat is also produced by compression, chemical means, 

 and electricity. For example, the temperature of air is 

 raised when it is compressed in a bicycle pump; when 



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