Singing Wine Glass
If the glass sings when you rub a wet finger along its rim, it’s made of fine quality crystal.
Is that a myth? Must be. Because I can make all the round rimmed glasses in my unchina cabinet sing. I don’t have any glass that I could qualify as high quality crystal or even expensive for that matter. But who cares? I can make them all sing so either I got lucky or the quality
part of it is a myth.
We had fun making our wine glasses sing yesterday. We even got waves to appear in the water. That was very cool.
What you need is:
A round rimmed wine glass
What you need to do is:
Place the wine glass on a firm hard surface like a table
Hold the wine glass by its stem
Dip your finger in the water
Run it along the rim exerting gently pressure on the rim
Don’t touch the sides of the glass
Lo! The glass should sing. If the myth is true and the glass is badly made, it won’t sing! But usually it does. I’ve got it to sing with a glass that had air bubbles in the glass.
The theory behind this is that as your wet finger slips and slides on the rim, it imparts energy to the glass molecules. The glass molecules start vibrating till they reach a frequency at which they resonate
Resonance is a forced vibration of particles and each material has a natural resonant frequency.
So what makes the sound? The vibrating glass molecules cause the air molecules to start vibrating at the same frequency. As your hand moves, it creates a wave of vibration in the glass molecules which is transferred to the air molecules. Sound is a wave. And the singing you hear is this sound wave, of air molecules vibrating at the same resonant frequency of the glass.
Why should you not touch the sides of the glass? Well, your hand will absorb some of that energy instead of the air molecules. So the sound produced will be lower and more dull.
So where do the waves in the water come from? As your hand moves, the sound wave moves with it. It, in turn, drags water molecules with it. You can see the waves clearly at the edge of the glass. Isn’t that cool? What you can do simply by wetting your finger and running it along the rim of the glass?
Why does Daddy’s glass sound different from mine, was the question posed by my daughter. She looked at the two glasses and soon figured out that he had more water in his than she did in hers. His made a deeper sound. Hers was a high pitched sound. The Indian musical instrument Jal Tarang
is based on this principle.
Resonance is quite an interesting subject. If you impart enough energy to the wine glass at its resonant frequency, it can shatter!! You won’t be able to do with just your finger though. This is one of the reasons why soldiers do not march in tandem when they cross a bridge. They could make it collapse by building up enough energy to make the bridge resonate and break apart.