122 ELEMENTARY SCIENCE 



effects. But to attempt to explain the cause of the causes 

 is philosophy rather than science. 



QUESTIONS 



1. What is the difference between potential energy and kinetic 



energy? 



2. What kinetic energy and what potential energy are involved 



in a watch? a cannon? a dynamo? a piece of coal? 



3. State Newton's Law of Universal Gravitation. 



4. Why does the earth move around the sun, instead of flying off 



into space? 



5. Would a piece of lead weigh the same at the top of Pike's Peak 



as at sea-level? 



