Making Sounds

Last weekend Nicholas studied a bit about Sound.

From the reading, he knew some facts about sound: sound is produced by vibration of materials - sound of piano comes from vibration of strings, his voice comes from vibration of his vocal chords....sound has to travel through materials. Sound travels very fast in air, faster in steels, but it can not travel through vacuum!

To make physical sense of what he read, we did a couple of experiments given in the book together. One is about the Glass music.

Nicholas took a wine glass, pour some water in it, and wet his finger. Following the instruction, he rubbed the glass' thin rim slowly with the wet finger while holding the base of the glass firmly on a table. Some sound was made. After a couple tries, the sound made from the glass became smooth and interesting. (Question: One has to wet his finger to make the sound, why? what would happen if one rub the glass rim with dry finger?)

Making sound from a wine glass

Justin was attracted to our experiments. He started to make some better sound; I commented that if he changed the water level, the sound he made would change pitch as well. He took my advice, rubbed the glass rim with full cup of water, poured some water out, rubbed the rim again,the pitch of the sound was higher; he poured some more water out, the pith was even higher; the pitch was highest when the glass was empty.

Nicholas then commented that if we had a lot of glasses with different water level of water in it, we could play music with the glasses. Indeed we can, in fact it has been done for some time - Nicholas found this moonlight sonata on glass harp online, right after the experiments. In the video, the music was made on different sizes of glasses.

This was a very interesting experiment - which made Nicholas learn, think and discover the secret of sound.

Note: change the water level in a given size glass, or change the size of glass sizes both change the glass' natural frequencies - i.e. the effect is the same, but change in size makes a more appreciable change in glass natural frequencies, and more obvious change in sound