Making Music with Harmonics

21 May 2006

Mandy - Well now we're off to Ely in Cambridgeshire to join Anna Lacey for this week's Kitchen Science. She's with Wendy, Sophie and Hannah who are waiting to find out about harmonics and making music with nothing more than a pink tube. Hello Anna!

Anna - Hello and welcome to the King's School in Ely where this week we're going to be doing some more sound and music experiments. So on this evening we've got our helper with us today, our science guru Wendy. What are you here to do today?

Wendy - Well we're going to be doing an experiment with a rather simple but strange-looking musical instrument.

Anna - Yes it does look very strange and very pink too! We've also got our student helpers. Can you introduce yourselves, names and ages please?

Sophie - Hi I'm Sophie and I'm thirteen.

Hannah - Hi I'm Hannah and I'm thirteen.

Anna - And what's your favourite thing about science then Sophie?

Sophie - Probably the practical side of it.

Anna - And you Hannah? Are you a budding science Einstein?

Hannah - I like doing the practicals as well.

Anna - So Sophie, first of all would you like to describe exactly what Wendy's holding here?

Sophie - It's quite long and it's a very nice bright pink. It's got a lovely bumpy texture to it.

Anna - It kind of looks a bit like a corrugated elephants' trunk. And so Wendy, what is it you want these girls to do with this strange pink pipe?

Wendy - Well if you take an ordinary pipe and spin it around your head, you wouldn't expect anything much to happen. So maybe if we ask Sophie first of all to give that a try. Takw this pipe, which is a bit unusual, and spin it around and we'll see what result she gets from this experiment.

Anna - Ok, so we're all just going to stand back in order to make sure that nothing bad happens and Sophie is standing there holding the pink pipe ready to twirl it round her head like crazy. So, go Sophie! (Noise). So we're getting some kind of eerie noise. Sophie, what did it sound like to you.

Sophie - I realised that it stayed at the same note. It gave me the shivers really.

Anna - I noticed that when Sophie was twirling it round her head she was doing it at the same speed and we had a note there. So what we're going to ask you to do is to try it at a different speed. So Wendy, you're quite a pro at this. Do you want to give it a go at a different speed?

Wendy - After years of practise, let's have a go. Let's see if we can get the note that Sophie just got and then go a little bit faster.

Anna - So Hannah, what was the big change there? What did Wendy do differently?

Hannah - As Wendy speeded up it went higher and when she slowed down it went lower.

Anna - Now Wendy, why exactly was that?

Wendy - Well the main thing that's different about this tube in comparison to a bit of hose pipe is the corrugations on the inside of the tube. So it's a very bumpy tube, and those bumps are not just along the inside of the tube but also on the inside as well. So if you feel the inside, the inside's corrugated as well. So there's two things that need to happen for this tube to make a noise. Most people know that anything that's making a sound is doing so because something is vibrating. What happens is, when I spin the tube around my head, the one thing that you'll notice is the long end furthest away from me is spinning much faster than this end that I'm holding.

Anna - So there's lower pressure near the far end of the tube.

Wendy - Yes because it's moving fast. So what you've got then is a pressure difference and the air is moving through the tube. With most musical instruments you get air moving through the tube by perhaps blowing it, but this is a different way of moving if you like. The most important thing is the corrugations. As the air is travelling through the pipe, it's getting to wider parts and narrower parts all the way along the tube. So effectively the air is getting jiggled about and very turbulent. It's this jiggling and turbulence that starts the vibrations and causes the sound.

Anna - So what's happening is while you're twirling that around like a helicopter, there's a pressure difference between the end near your hand and the end at the far end of the tube which pulls air through like a wind tunnel. But then the air doesn't move through slowly, it actually gets jiggled about and that makes a noise. So why does it change then when you do it at a different speed?

Wendy - There's a certain number of vibrations that you can set up in this length of tube. So the speed that you're vibrating the air at affects the number of waves you can fit into this tube. If you've got that happening in air, what you hear are these specific different notes. You can't get every notes of the scale; you can only get certain notes.

Anna - Ok, so does this have anything to do with harmonics?

Wendy - Yes, that's what these basically are. We're listening to the harmonics of a pink tube instrument. Many musical instruments have this and many musicians will know these notes as the harmonic series and lots of people who play instruments have the ability to change the harmonics they hear by just tightening or changing the way their lips vibrate.

Anna - So musicians are actually performing proper sound science every time they pick up an instrument. That's just amazing if you ask me. But something even more amazing than that, Wendy, you can actually play a tune on this amazing tube.

Wendy - Yes, it's something to be very proud of after seven years of practising. I've put together five notes that I can get out of this tube, and if you put them together in a certain order, hopefully I can make a tune that some of the listeners might recognise.

Anna - For your listening pleasure, Wendy from Science Made Simple plays us a tune with a pink pipe. (Tune) So can you just enlighten us as to what the tune actually was.

Wendy - Yes it was the last post which you often hear played on a bugle on Remembrance Sunday.

Anna - That's absolutely wonderful. So what did you think of that Sophie?

Sophie - Excellent. I don't know how she does it?

Anna - And what did you think of the science behind all that?

Hannah - I thought that was very interesting how she can make a song out of just one pipe.

Anna - It's true. You heard it here first on the Naked Scientists in our Kitchen Science. Well that's all for this week. Thanks very much to Wendy, Sophie and Hannah and the King's School in Ely. We'll be back next week at another school in the Eastern Counties for some more Kitchen Science. Goodbye.

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