Chemistry

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Materials

• 1 skewer, or similar sharp item
• 1 balloon

Video

Explanation

The balloon consists of long molecules called polymers. They are like long spaghettis. These polymers bond together with chemical bonds called cross-links, just like spaghettis sticking together.

It's these cross-links that hold the balloon together, even when it's stretched. However, only to a certain point. If the polymers are pulled apart too much, the cross-links will break.

When you inflate a balloon, not all parts are stretched equally. At the opening and at the top, the least stretching takes place and the balloon retains much of its thickness there. This can be seen by the balloon being darker (less light penetrates).

When you insert the skewer there, some cross-links will break, but since the balloon is not so stretched there, the remaining cross-links are enough to hold the balloon together.

If, on the other hand, you insert the skewer into the side of the balloon, it will pop. Here the stretching between the polymers is so great and breaking some cross-links leads to too much force on the remaining ones, and they also break. Some cross-links here probably broke already when the balloon was inflated.

Even if the balloon doesn't pop, air will still leak out at the holes.

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 happens when I change the type of balloon?
• What happens if I change how much I inflate the balloon?
• What happens if I use a sharper object?
• What happens if I use a thicker object?

Variation

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