THE PENDULUM. 



75 



EXEECISES. 



21. How will the times of vibration of two pendulums compare, 

 their lengths being 4 feet and 49 feet respectively ? Ans. As 2 to 7. 



22. Of two pendulums, one makes 70 vibrations a minute, the 

 other 80 vibrations during the same time ; how do their lengths 

 compare ? Ans. As 49 to 64. 



23. If one pendulum is 4 times as long as another, what will be 

 their relative times of vibration? 



24. The length of a second's pendulum being 39.1 inches, what 

 must be the length of a pendulum to vibrate in second ? 



25. How long must a pendulum be to vibrate once in 8 seconds ? 

 In $ second ? 



26. How long must a pendulum be to vibrate once in 3^ seconds ? 



27. Find the length of a pendulum that will vibrate 5 times in 4 

 seconds? An*. 25.02 + inches. 



28. A pendulum 5 feet long makes 400 vibrations during a certain 

 time ; how many vibrations will it make in the same time after the 

 pendulum rod has expanded half an inch ? 



Recapitulation. In this section we have considered 

 the Simple Pendulum ; the Compound Pen- 

 dulum ; the nature of the Motion of the Pendu- 

 lum and its Cause ; the meaning of the terms Vi- 

 bration, Time of Vibration, Amplitude of 

 Vibration; Centre of Oscillation; Real Length 



