Chemistry

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Video

Materials

• 1 straw
• 1 pair of scissors
• 1 small glass jar (for example an empty baby food jar)
• 1 raw potato

Explanation

This demonstration clearly shows that air really consists of something. When you cover the straw opening with your thumb, you capture the air inside. When you hit the straw against the potato, the air in the straw is compressed, at the same time as it presses against the sides of the straw. When the straw is stretched like this, it gets stiff and is prevented from bending. You can try not to keep your thumb on the opening - it will not work. The air is now pushed out through the upper opening.

Air is a mixture of chemical substances in a gaseous state. These chemical substances are mainly dinitrogen and dioxygen, but also smaller proportions of, among other things, carbon dioxide, water and argon.

Experiment

You can turn this demonstration into an experiment. This will make it a better science project. To do that, try answering one of the following questions. The answer to the question will be your hypothesis. Then test the hypothesis by doing the experiment.

• What other fruits and vegetables can a straw be passed through?
• What happens if you use a thicker straw?
• What happens if you a longer straw?

Variations

After you have pierced the straw and one end of it has been blocked by a french fry, you can turn the straw over and do the same thing with the other end. When you now have a french fry in each end of the straw, you can strike again - without holding your thumb over the opening of the straw. With some luck, one of the french fries will fly straight up in the air! For me, this only worked once in twenty tries.

If you have some kind of plastic pipe, you can make a neat cannon. Push the tube through, for example, a potato or an apple to create a stopper at each end. Then take a strong stick of some sort and push one of the stoppers. The other stopper will then shoot out at high speed.

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