Internet Version [Naruhodo no Mori] Vol. 3

by Yumiko Mori

Toshi and Tae are watching the bottle carefully.
Some cracking sounds.

Tae: "Oh, the bottle made dents by itself!"
Toshi: "Tae,the bottle didn't made these dents. Actually the air outside the bottle pushed the surface and made those dents."
Tae: "What do you mean?"
Toshi: "The air inside the bottle lost its energy when it cooled down. This is the reason why the inside air was pushed by the outside air."
Tae: "I don't understand yet. What do you mean the air lost energy?"
Toshi: "Air is made from very small particles, called molecules. They are usually moving around at very fast speeds. Molecules move faster at higher temperature. But when temperature goes down, molecules move slower."
Tae: "That's interesting. It sounds like the air is alive."

Toshi:"The air also has its own weight."
Tae: "Is that true?"

Toshi: "We are living without noticing the air has its own weight. One liter of air weighs about 1.2 gram. That is about 1/800 fraction of water. But if you add up weight of all the air inside this small room, it could be more than 10 kilo gram. That's quite heavy, isn't it?"
Tae: "I guess the weight is the source of the air pressure. That means we can not do this experiment in space where there is no air."
Toshi:"Yes, you are very right! The air doesn't fly away from the earth thanks to its own weight. Besides we, human being, can't live without air."
Tae: "Toshi, let's try the experiment one more time!"
Toshi: "OK, maybe we can see how lively the air is today."

Air Pressure Experiment Part 1

You can do this experiment within 10~20 minutes. This is a veryeasy one.

Materials

• An empty plastic bottle.

• A coffee cup

• Hot water (70~80 Celsius: or 160~175 Fahrenheit)

Methods

1. Pour a cupful of hot water from the coffee cup into the plastic bottle.

2. Shake the bottle well so that the bottle is filled with hot steam. Be careful not to touch the bottom of the bottle. It is very hot.

3. Screw in the cap, put the bottle on a table, and watch what's going to happen. After 4~5 minutes you will hear cracking sounds and then dents should appear on the bottle.

Air Pressure Experiment Part 2

If you happen to have pieces of dry ice, try this experiment.
Required time: 10 minutes

Materials

Small pieces of dry ice A plastic film case for 35 mm film

Methods

1. You put a piece of dry ice into the film case. The size of the piece should be about 2 cm (or 3/4 inch) in diameter.

2. Put the cap and place the film case on the floor. Make sure that lighting fixture or some other obstacles on the ceiling is not right above the film case.

3. Stay away from the case and wait.

4. Within 2~3 minutes the cap will be shot up and hit the ceiling with loud noise.

Never put your face right above the case!!!!

• Do not use this method to scare other people.

• You can not preserve dry ice even in the freezer. So you should plan to do this experiment soon after you obtain dry ice.

• You could use a plastic bag as a substitute for a film case. In this case, air pressure make a hole on the bag.

• Dry ice is frozen carbon dioxide.

• If you put a piece of dry ice into a glass of juice, the juice will be turned into carbonated juice.

• It was very amazing to realize that the evaporated carbon dioxide in the film case pushed the cap open.

   I am neither a scientist nor a school teacher. I am just a mother of three children. I feel very happy when I and my children are together working on science experiments. We are only doing quite simple experiments, but those give us such enjoyment. We often like to do these experiments repeatedly. When you read a science experiment book, you may already feel that you master the subject simply by reading it. But you can understand much more if you actually try experiments by yourselves. When my children and I work together on experiments, conversation starts between us. We learn together and have fun together. I think these moments are so precious.

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