2 MATTER AND ENERGY 



happenings in turn. So then let us enter upon these 

 studies resolved not only to learn all that we can but 

 also to search deeply into each new fact until we fully 

 understand it. 



2. Physics. It is easy to see that if science is the 

 study of common things, it must include a great number 

 of subjects that are very different from each other. In 

 order to separate these subjects so that each may be 

 treated more simply, scientific study is divided into 

 many branches, such as physics, chemistry, botany, 

 geology, and others. Still these branches are more or 

 less related to each other, the teachings of one often 

 being applied to several of the others ; in fact, one 

 could hardly know any of the sciences well without 

 knowing something about one or more besides. The 

 teachings of physics are perhaps most generally used, 

 and for this reason it forms a natural starting point 

 for our study. 



In its broadest meaning, physics is the study of matter 

 and energy. Concerning matter, physics treats of such 

 changes as affect its forms and motions. 



3. Matter. To understand this definition it is neces- 

 sary to know first what is matter. No one can really 

 tell what matter is it can only be described ; and it 

 occurs in so many forms and has such various features 

 that no full description would apply to all sorts of mat- 

 ter. Some kinds are of one color and some another, 

 while many show no color at all ; different kinds vary 

 in weight; there are hard substances and soft; and in 

 many other ways we look in vain for features which 



