PRESSURE IN GASES 45 



5. When a substance is compressed what happens to its mole- 

 cules ? What sort of matter can bear most compression ? Why ? 



6. Explain why compressed gases exert force. Name any uses 

 of compressed air that you know of. Is a hollow rubber ball more 

 elastic with or without a hole punched through it ? Why ? 



7. Why do balloons rise into the air ? How does the weight 

 of a balloon compare with that of the volume of air that it 

 displaces ? 



8. Why cannot a balloon rise to unlimited altitudes ? Which 

 could rise higher, a balloon filled with hydrogen or another filled 

 with hot air? Why? 



9. Explain the use of compressed air in a bicycle tire. 



