A noisy, amusing demonstration of the physics of music. It can take a bit of practice to get exactly right, but it's well worth the effort.
- straws (need to be straight – cut off the bendy bits if there are any)
- Flatten one end of the straw ~2cm from the end to the tip.
- Make two cuts in the now flattened end of the straw, to form a triangular tip.
- Insert the triangular tip of the straw into your mouth and blow hard. You should hear a loud 'buzzing' sound.
- While blowing on the straw oboe, get a volunteer to cut the straw shorter, ~1cm at a time. With each cut you will hear the pitch of the oboe sound go up.
How Does it Work?
The flattened triangular tip acts like the reed found in most wind instruments. Blowing on the reed causes the straw to vibrate. A standing wave pattern is created along the length of the straw, which we hear as sound. As you shorten the straw you shorten the wavelength of the standing wave pattern and therefore increase the pitch of the note.
Tips for Success
It can take some practice to get the right sound – if it doesn't work straight away then slowly move the straw in and out of your mouth whilst still blowing until you hear the sound. Definitely a good demonstration to practice before performing it in front of an audience!
This is a good demonstration to attract a crowd due to the amount of noise involved. Younger kids in particular will love hearing the effect of the pitch going up as the straw is cut shorter and shorter. They will also enjoy making their own straw oboe as part of the demonstration, which they can keep afterwards.
Did You Know?
As long ago as the fifth century BC Pythagoras and his followers were experimenting with standing waves and calculating the values of their harmonics. Another way to set up a standing wave is to blow across the top of a beer bottle. In this case the note gets deeper as you drink the beer (sorry, tune the instrument). Pythagoras refused to let his followers eat beans for fear of flatulence; fortunately, no such effects are associated with beer drinking.