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In this post I’m sharing three simple and fun air pressure activities for kids. If your kids are young, you can simply do the activity and let them marvel at the outcome. If your kids are older, I’ve included some of the science behind each activity to help them learn more about air pressure. I hope you enjoy!
Note: Find more awesome science activities on my Science Activities for Kids page.
#1: How does the paper towel stay dry?
This first demonstration is extremely easy to prepare. Take a paper towel and shove it into the bottom of a glass.
It should be packed in tight enough that it will remain in the bottom of the glass even when the glass is turned upside down.
Next, fill a sink or container of water. The depth of the water should be equal to or greater than the height of your glass.
Place the glass, upside down, into the water. It is important to place the glass straight down into the water without tilting it to the side.
Then lift the glass from the water. Remove the paper towel. Your kids will notice that the paper towel is still dry.
So how does the paper towel stay dry?
The air pressure in the glass pushes the water away, so that the water cannot go into the glass to get the paper towel wet. Even if the water on the outside of the glass completely submerges the glass, the air pressure in the glass prevents the water from entering.
#2: How does the cardboard float?
For this activity, you will need a cup and a small piece of cardboard that completely covers the opening of the cup. In lieu of cardboard you could also use a paper plate.
Start by placing the cardboard on top of the cup, and then turning the cup upside down. The cardboard will fall off. Ask your children why the cardboard falls. They may mention gravity.
Then, fill your cup most of the way with water. Place the cardboard back on top of the cup.
Use your hand to press the cardboard firmly to the cup while you turn the cup upside down. Then remove the hand holding the cardboard in place. Watch as the cardboard stays firmly attached to the cup without falling. It will appear to float in place.
(Note: Although the cardboard should stay firmly attached to the cup, you may want to try this experiment over a sink or bathtub to prevent any major spills just in case.)
So why doesn’t the cardboard fall after you turn the cup upside down? What makes the cardboard stick firmly to the cup? There are actually two unrelated effects that are responsible.
The first effect is that of water surface tension. Water has a tendency to stick to itself and other things. Thus, assuming the cardboard or other object you have used has a fairly flat surface, the water will create a sort of seal between the cardboard and the cup. This seal means that the air outside the cup is not able to get in.
The second effect is that of atmospheric pressure. Basically, for their cardboard to fall, the air outside the cup would have to get into the cup. But because the water has created a seal between the cup and the cardboard, the air outside the cup can’t get in. So the cardboard has nowhere to go but to stay firmly attached to the cup. In this case, the force of air pressure pushing up on the cardboard is greater than the force of gravity pulling the cardboard down.
#3: Why can’t you blow up the balloon?
For this activity, you will need a balloon and a large plastic bottle (a 2 liter soda bottle would work well).
Prepare this activity by inserting the balloon into the bottle. Fold the edge of the balloon around the neck of the bottle. Now, invite your children to blow up the balloon. They won’t be able to!
Why can’t you blow up the balloon when it is inside the bottle. The answer has to do with air pressure. As you blow up the balloon, you are adding more air to the same small space inside the bottle. Soon, the air pressure inside the bottle becomes too great, making it impossible to add more air.
If you want, you can now cut a small hole into the bottom or side of the bottle. Once you have cut a hole, it should now be possible to blow up the balloon. This is because as you add air to the balloon, air will leave the bottle through the hole to make room for the air you are adding to the balloon.
More resources for learning about states of matter
More states of matter posts from Gift of Curiosity: