Physics

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Video

Materials

• 1 drinking straw
• 1 pair of scissors

Explanation

In air, sound consists of waves of denser air, moving from the source of the sound. Here, the straw works like any wind instrument. Inside is a column of air that can be made into waves. The length of this column of air can be changed and thus different musical notes can be obtained.

The air inside the straw is made into waves by the homemade mouthpiece. When you blow, the two tips hit each other very frequently. Just as water waves start if you hit a water surface, sound waves start here when the mouthpiece hits the air. The sound waves spread out through the open end of the straw and reach your ears.

The air column in the straw, and anything else that can vibrate, can only do so at one or a couple of speeds and can thus only be heard as one or a couple of notes. Exactly how fast something can vibrate depends on a number of factors, but the factor that can change here is the length of the air column. A short straw gives a fast vibration and short sound waves, which we humans perceive as a high note.

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 if you make the straw shorter?
• What happens if you make the straw longer (you can do this by placing another straw over the first)?
• What happens if you use a wider straw?
• What happens if you use a slimmer straw?

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