98 APPLIED SCIENCE 



7. Why do we fan ourselves when we perspire? 



8. Why must the bung of a barrel be removed in order to secure 

 a proper flow of liquid from the faucet? 



9. Why does high mountain climbing often cause pain and 

 bleeding in the nose? 



10. Small packages and folded papers are often transmitted in 

 a carriage by air pressure through brass tubes called pneumatic 

 dispatch tubes. An exhaust pump is attached to one end of the 

 tube in which a tightly fitting carriage moves, and a compression 

 pump to the other. If the air is half exhausted at one end and has 

 twice its density at the other end, find the propelling force on the 

 carriage if the tube is 4 in. in diameter. 



11. Explain why it is impossible completely to exhaust a vessel 

 of air by an air pump. 



12. A pneumatic hammer, often called an "air gun," is used to 

 drive rivets. Explain how it works. 



13. Explain the care of a pneumatic hammer. 



14. What is the practical value of a barometer? Explain the 

 principle of a barometer. 



15. Why is compressed air used in building a subway? 



16. What advantage has compressed air over electricity in 

 transmission of power? 



17. Give some of the advantages of a pneumatic tire over a 

 solid tire of the same size. 



18. The general shape of boats and air-ships is usually made to 

 conform to that of a fish. Why? 



19. What is a fog? 



20. What is a cloud? 



21. Why is a bottle of hot water better than a hot stove cover 

 for keeping your feet warm in bed? 



22. Explain the principle of science underlying pneumatic 

 machines. 



23. Is it possible to measure gas pressure with the same gauges 

 that are used to measure the pressure exerted by liquids? 



24. How is air compressed? What is the commercial method 

 of compressing air? 



