Twang on a can

Here, as unwisely promised yesterday, is a clip of me twanging the ring-pull of an aluminium fizzy drink can whilst simultaneously filling it with water. What do you think happens to the pitch of the note?

My own, subjective and non-scientific, opinion is that the pitch stays the same. The note seems to get higher because the upper harmonic partials are increasingly favoured as the can fills. If I were to blow the can like a flute then I would hear the air inside vibrating. Less volume of air, as the water replaces it, means a gradual rise in pitch. When I twang the can it is the can I hear resonating. The water dampens (no pun intended - 'deadens' might be a better word) the sound of the lower partials.

Today I went for a long walk by the sea so no sonic experiments. But tomorrow I shall continue to explore the seasonal debris and make some more rubbish instruments. If you would like to join in then hang on to all sizes of bottles, both glass and plastic, tin cans of various types, wrapping paper and anything else you think might produce a noise.

These instruments are rubbish

Before you consign the debris from your seasonal festivities to landfill and the recycling banks why not have some fun with it first? That is certainly my own intention and I'm starting with some fizzy drinks cans. I had a grand plan which I'll reveal tomorrow but on the way I noticed a thing or two. You may know that all plastic bottles of the same size play the same note if blown like a flute. Well aluminium cans are the same although it is not nearly as easy to produce a sound in this way. However, when you twang the ring-pull (which remains attached to the modern can after opening) the pitch varies betrween cans. Of the five cans I tried the pitch varied between G and Bb. These cans were all the same brand from the same multipack. Although the cans all contain the same volume of air there must be other variations in their construction.

The next thing I did was to twang the ring-pull as I gradually filled a can with water. It requires a steady hand. (Using a funnel has a deadening effect.) Why not try this now? I'll post a movie of my own experiment tomorrow. Before you begin, though, what do think will happen to the sound as you pour in the water? Does experience tally with your prediction?