The Straw Flute

What to Do

You will need the following items for this experiment:

• Straw
• Scissors
• Someone who can blow really hard

Here's what you do:

• Take the straw and the scissors, and cut off the tip of the straw to a point, like so. (Try to get both sides to be the same!)

• Now, gently chew on the straw to soften the tip, and to get the edges to be smooshed together. You would like the two tips to be almost touching each other.
• Now, take the person who can blow really hard, and have them put the pointy end in their mouth, and blow really hard. If they do it right (it might take some practice), they will get a very loud sound from the flute!

Now, try some of these things:

• Cut the non-pointy end of the straw off. What does this do to the tone?
• Can you cut holes in the straw so that you can play it like a real flute?
• Maybe you can take a second straw, and slide it over the first. This would make sort of a straw trombone!

There are all sorts of different musical instruments you could try. And there is some good analysis you can do. We use this in physics labs to measure the speed of sound!

What is Happening?

When you blow on the end of the straw, the two pieces of the tip vibrate together. This makes a vibration, which is necessary to make sound. But the tips don't just vibrate at any old frequency. No sir! The vibration travels down the straw, and reflects from the end. This sets up a wave in the air in the straw; the vibration will bounce back and forth between the two ends. It is this vibration that you are hearing! Changing the length of the straw (by clipping it off, or by making a straw trombone) changes the time necessary for the vibration to travel up and down the straw, and so changes the pitch. And making a hole in the straw, so it is like a real flute, lets the vibration bounce off from where the hole is, which will also change the pitch!

So this is not just a musical instrument, it is a physics experiment!

Other Things to Try

How do different size straws work? Does this make a difference? You might also try different designs for the tip. Which one works best? And does it make a difference how hard you blow? There is a lot of experimenting to be done here!

The contents of the page was modified from that created for the
Little Shop of Physics, Colorado State University

Follow-up

1. What makes the tip of the straw vibrate? Why is vibration necessary?

2. Describe how the vibration travels within the straw.

3. How is the air within the straw affected by the traveling vibration?

4. Changing the length of the straw affects two variables. What are they?

5. The article mentions three ways to change the distance that the vibration travels. What are they?

6. How do different size straws work? Does this make a difference? Which one works best?

 Obtaining credit for your efforts Print a copy of the blank laboratory write-up paper. Read and complete each section, incomplete write-ups receive no credit. Have your parent check your work and sign the paper.