172 MECHANICS 



2. What are the sources of heat and light? Can you 

 obtain heat without light, or light without heat? 



3. What is a porous body? Can it be changed so 

 as not to be porous? Is there any advantage in having 

 bodies porous? Name one very important porous body* 



4. Name all the uses of water. 



5. What should we do if we wish to keep in good 

 health? 



6. If a clock is going too slowly, what should you 

 do to regulate it? Explain. 



7. What is a force? What can forces do? 



8. Name two ways by which you can exert a large 

 force by using a small force. 



9. What effect have forces upon elastic bodies? 

 What use is made of this effect? 



10. What are machines? What are the uses of 

 machines? 



