Was putting away the champagne and wine glasses from our New Years celebration and asked Gregory to bring them back out to the dining room so I could put them away. As they are crystal I asked him carry only two at a time. However, as my little man loves to make music, he still managed to clink them all the way there each trip.
I explained to him my reasoning for asking him to only carry two at time and why we would prefer his caution – in that crystal glasses are more easily broken than regular glass. That’s when I remembered what else crystal glasses do that make them so unique.
They can SING!
We brought one back out to the kitchen and I filled partially with water and showed him how it sings. He then tried it himself and asked how. While I know it works – I’m not sure how – so…(you guessed it!) we “googled” it. What we found was really cool!
The Mechanics (I had no idea – but now I do):
- The principle at work here is a “slip-stick” form of friction. It is also called “dry-damping.” When the fingertip circles the rim of the glass, it excites the glass molecules. They follow the motion of the finger around the glass, in effect “stretching” in the direction of the moving finger. The frictional force is high as the molecules stretch.
- The elastic forces within the glass pull the molecules back into place, but because of inertia they overshoot and go too far. At this point, the molecules are moving in the opposite direction of the finger. The frictional force is low. The stretching and returning action of the molecules becomes a cycle. An imbalance in the frictional forces is created, causing the vibration that makes the sound.
- This illustrates the fundamental natural frequency of the glass. Different glasses have different frequencies, which depend on factors such as the size of the glass, the position of the glass and the volume of liquid in the glass.
- Regular glass is “soft” glass. It has high internal friction (molecular) so that sound waves produce a dull sound. Crystal contains lead, which makes it “harder,” with very little internal molecular friction: molecules are freer to follow the fingertip. This creates the clearer sound in crystal.
- Regular glass can make a rim sound, although with more difficulty, and the tone has less quality.
What was even better than the description on how and why was finding videos on people creating amazing sound using these techniques. Here’s my favourite of the day….
Just think: wine glasses + water +a wet finger + friction = beautiful ethereal music. What else do we have so easily at our finger tips which could create something totally different than what we currently use it for?