Tin Can Bongos

What you need

1. Lots of empty food cans. Look for the ones which have crimped lids at both ends - so top and bottom look identical. You'll need 4 or more cans per musical instrument.
2. A can opener.
3. Tape. Ordinary sticky tape will do, but best of all is electrician's insulation tape - you can stretch it a bit to make it really tight.

What you do

1. Be very, very careful of sharp edges. Good can openers will leave a smooth edge, but it still can be sharp. Take care when handling the can!

2. Keep one can back - we'll come back to it in a moment.

3. Wash the cans out, and remove both ends from them.

4. Join the cans end-to-end, and tape them very tightly, so you're making a single, rigid cylinder.

5. A cylinder three cans long is enough, but four, five or six cans will work too.

6. Go back to the can you held back, and add it to the end of your cylinder so you have a tube, closed at just one end.

It may not look like much, but you've just made a musical instrument. Hold it lightly, and bash the closed end on the ground - you should hear the cylinder ring with a surprisingly pleasant note. It seems to work best on carpet, and if you tilt the tube slightly so you're bashing the rim at an angle rather than the end, flat-on.

If you make a number of cylinders of different lengths you'll find they play different notes - so you can drum away to your heart's content.

What's going on

Hitting one end of the bongo causes the cans to vibrate, this vibration is transferred to the air inside them. The frequency of vibrating air determines if it is a high note or a low note. At the beginning all notes are played in the tube but soon many die away. A closed pipe like this has a natural frequency, this is the frequency which the pipe 'encourages'. While the other notes are lost, this note dominates and that is what you hear.

Longer cylinders have a lower natural frequency - a lower note.

Our assumption is that the main wavelength of note produced is a little over twice the length of the tube, but without investigating with a spectrum analyser it's hard to know - let us know if you try. More mysterious is why the sound produced is so pleasant, when you'd expect a ghastly metallic clank. But then, musical instruments - even ones made out of old soup tins - are more an art than a science.

Special Safety Advice

Be very, very careful with the can opener and the sharp open cans - ask an adult to help you. You shouldn't waste good food, if you save your cans up for recycling anyway you'll already have a supply!