Here’s a neat party trick to impress your friends.
Rub your finger around the rim of a wineglass and friction causes it, and any liquid it contains, to oscillate. When this vibration produces an audible pure tone, the wine glass is said to “sing”.
Now Ana Karina Ramos Musalem and pals at the Weizmann Institute of Science in Israel have shown how to couple one singing wineglass to another so the second wineglass sings without anybody touching it.
The trick is to place both wineglasses in a sink of water (without the water overflowing into the glasses). Rubbing one so that it sings should make the other sing too. This phenomenon is known as phase-locking and is also responsible for populations of crickets that chirp together and fireflies that flash together.
Phase locking depends on the strength of the coupling. This is greatest when the glasses are closer together and when their resonant frequency is similar. So if you run into trouble, try moving them nearer to each other and matching their frequencies by changing the amount of water in each glass.
Then watch as jaws drop around the dinner table.
(With apologies to Maya Angelou.)
Ref: arxiv.org/abs/0901.0656: Phase locking between two singing wineglasses
[…] Lembrei disso por causa de um artigo publicado no arXiv por pesquisadores israelenses que fizeram duas taças próximas uma da outra cantarem juntas, esfregando apenas uma delas. A taça parada ao lado da taça cantante recebe as vibrações da vizinha e começa a cantar também, no mesmo tom. Os autores do experimento mediram as vibrações com uma aparelhagem simples, que dá para montar em qualquer laboratório didático de física. (via the physics arXiv blog) […]
Please update with clarification on how deep the water in the container has to be. Just below the top of the glasses?
The team don’t give the size of their wineglasses. But they do say they experimented with different heights of water in the container (11, 12 and 13 cm) and report that it has little effect on the outcome.
The glasses are about 16-18 cm in hight, It is better to put enough water as high as the widest point of the glass, but it will start working even with much less than that.