38 



Our Surroundings 



One has only to observe the effects of wind to be convinced that 

 air flows. That it is actually matter, a real substance which oc- 

 cupies space and exerts pressure, is not so apparent. Experi- 

 ments, however, will show that these statements are true. 



Experiments to Show Properties of Air. To show that air 

 occupies space, press an empty tumbler upside down into water. 

 You will notice that it is not easy to fill the tumbler held in that 

 position. Why ? 



Close one end of a piece of glass tubing about a foot long. 

 Then insert the open end into a jar of water. Does water enter 

 the tube? If not, why? Open the upper end of the tube, still 

 holding it in the water. Does water rise in the tube? If so, what 

 does it displace? 



Blow air into an empty toy balloon and notice what happens. 

 After these experiments, do you conclude that air does or 

 does not occupy space? 



Hold in the hand a piece of thin board about two feet square 



and swing it edgeways through 

 the air. Is there much resist- 

 ance? Then swing the board 

 broadside through the air. Is 

 there more resistance than in 

 the first case? If so, why? 



To show that air exerts 

 pressure, hold a glass tumbler 

 under water so that the water 

 completely fills it. Then place 

 a sheet of cardboard over the 

 opening of the tumbler under 

 the water. Turn the tumbler 

 bottom up, holding the card- 

 board close over the opening, 

 and lift the tumbler from the 

 water. Then remove the hand from the cardboard. Does the card- 

 board remain in place and the water in the tumbler? If so, why? 

 Again, take a tin can having a small opening in the center of 

 the top, and another opening in the center of the bottom. Close 



AIR HAS WEIGHT 



