418 . GENERAL SCIENCE 



a certain number of air vibrations per second. For example, the sound which 

 has 256 vibrations per second, or 258.6 vibrations (musical scale), produces the 

 tone C. 



FIG. 3086. -If a piece of paper is held on 

 FIG. 308a. the teeth of the wheel the pitch will 



rise as the speed increases. Why? 



QUESTIONS 



1. If a book fell off the table and there were no one around to 

 hear it, why would there be no noise? 



2. What causes the " snap " of a whip? 



3. Why are you able to make a noise by clapping your hands? 



4. Why does not waving the arms produce a noise? 



5. Which talks faster, man or woman? Prove your answer. 



6. Why do soldiers on the march " break step " while marching 

 across a bridge? 



7. Why is it necessary to place the sign " Walk your horses 

 across this bridge " over the entrance to some bridges? 



8. How far away wo'uld a flash of lightning be if we heard the 

 thunder 15 seconds after we saw the flash of lightning? 



9. If it were possible to hear and see an explosion on the moon, 

 how long after the explosion would we see it. and how long afterwards 

 would we hear it? 



10. If the people on Mars could see what we are doing, how long 

 after you did a thing would they see it? If they could hear, how 

 long after you said a thing would they hear it? 



11. Why would there be no sound from a bell in a vacuum? 



12. Why do windows of a house break when a terrific explosion 

 occurs? 



13. Why does a shell or bullet whistle? 



