1-HVSK \l. PRELIMINARIES 



Heat is one of the forms which energy can take. When 

 a man raises a weight some of the energy he expends in 

 his muscles takes on the form of heat, while some is used 

 in doing the work, and this portion of the expended energy 

 remains in the raised weight, and confers upon the weight the 

 power of doing just the same amount of work when it is let fall 

 to its old position again. None of the energy the man expends 

 is destroyed ; part appears as heat and part remains in the 

 raised weight. Just as material or matter may be changed 

 into other matter but cannot be destroyed, so energy may 

 assume different forms, such as heat or light, or be stored in 

 the object on which work is done, but cannot be destroyed. 



The energy which appears as heat passes away from the man 

 to the things around him, both to the things in contact with 

 him, by conduction, as it is called, and by passing through 

 space to things away from him, by radiation, as it is called. 

 The energy is by these and other means scattered and rendered 

 unavailable for doing work though it is not destroyed ; it is 

 said to be dissipated. 



