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MORE BALLOON-AIR PRESSURE FUN
Balloons are neat teaching tools! We can perform some more experiments with balloons to learn more about air pressure.
Blow up a balloon until it is slightly larger than the mouth of a large empty bottle. Tie the neck of the balloon with a rubber band, then wet the balloon and the mouth of the bottle to make them slippery.
Try to force the balloon into the bottle without letting the air out of the bottle. That is to say, if we press the side of the balloon a little bit, with a pencil or something that goes down into the bottle, it will make a passageway through which some of the air in the bottle can leave the bottle. Then, the balloon could go inside. The air pressure inside the bottle is what keeps the balloon from going inside the bottle.
Let's do this a little differently and see what happens. Deflate the balloon and place it inside the bottle, a cup, or a glass jar, with the neck of the balloon up, so we can inflate it.
We'll blow up the balloon as much as possible, and lift it by its neck.
You will see that the sides of the bottle compress the balloon, which, in turn, increases the air pressure inside the balloon.
The pressure is great enough to hold the object containing the balloon so firmly in place that when the balloon is lifted, the object is lifted too.
With the bottle sitting on the countertop where it is safe (just in case it should drop), let's put a little dishwashing detergent on the outside of the balloon before putting it inside the bottle or jar, and see if the air pressure can still hold that slippery balloon inside the jar.
If it slips out of the jar, we will have learned something about lubricants as well as about air pressure.
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