EXERCISE 8 A 



WHAT EFFECT IS PRODUCED UPON A VOLUME OF AIR BY A CHANGE 



IN ITS TEMPERATURE? 



Materials. A toy balloon well inflated ; a refrigerator (may be made by placing a piece of ice in 

 a covered box or pail) ; one of the schoolroom radiators, hot-air register, or a heating stove. 



Directions. Measure the circumference of the balloon accurately. Record the measurement. Place 

 the balloon in the refrigerator for fifteen minutes, then quickly measure the same circumference again, 

 and record. Then place the balloon above the radiator, register, or stove for fifteen minutes and meas- 

 ure in the same way again. Compare the three sets of measurements, and explain any differences. 



Additional problems. Balloonists report that when a cloud remains between a balloon and the sun for a 

 time, the balloon begins to descend, and ascends again when the sunshine falls upon the balloon. Explain. 

 Why do balloonists find it difficult to remain afloat at night ? 



[10] 



