Gravity is Optional

We know that bells ring and that organ pipes resonate. In fact, most musical instruments work by controlling resonance.

The corollary is that anything that resonates at audible frequencies can be used to make music.

Water glasses | Rods | Bowls | Tacoma Narrows Bridge

Water glasses

If you rub a wet finger around the rim of a drinking glass (sadly, it won't work with most plastics), you can produce a sound that is very hard to locate. This is due to resonance. Some people have been able to play tunes using a collection of glasses, tuned by adjusting the amount of water in each glass.

However, his explanation of WHY the frequency changes when the amount of water changes - the amount of water causes the speed of sound to change - is totally ridiculous. Everyone "knows" that longer organ pipes produce lower tones (frequencies) because of their length. Therefore, it follows that less water produces a larger resonance cavity and, by direct analogy, will cause a lower tone. Since his description was obvious nonsense, I performed several experiments. It is absolutely true that less water produces higher frequencies - proving, without a doubt, that the size of the empty space inside the glass is NOT the primary factor in producing a given frequency. Additional experiments indicate that, by tipping the glass, different frequencies can be produced without changing the amount of water. What appears to be happening is that when the glass vibrates, the shape of the open part changes. Basically, opposite sides move toward and away from each other. (You can see this happening in the next video.) The speed of this deformation is affected by how much mass needs to be moved. Thus, more water means more mass, slower vibrations, and a lower frequency - just as reported in the video.

The glass armonica, invented by Benjamin Franklin in 1761 AD, uses a collection of different size glass resonators (similar to bowls or bells) mounted on a rotating shaft. The only real difference is that the glass moves while the finger stays still.

To see how a glass vibrates, check the following video at about 2:55.


We saw this at the 2010 DC Science and Engineering Fair. The idea is to slide your fingers along a metal rod. To make it work, just add some violin rosin. (Yes, it IS sticky .. that is why it works.)

To make it work, hold the rod in the exact center (where it balances). Then, slide your fingers along the rod from the center to the end. If you can get it to work, the sound is deafening. Everyone within 5 feet of you will ask you to "please" quit. (I suggest you do. The word "please" in this context means that if you don't bad things might happen - :)

The person that demonstrated this to us said that it would only work on solid aluminum rods.

Well, since we don't believe anything other people say (until we have verified that it might be true), we tried other pieces of metal. We have verified that it also works on

Thereby proving, beyond all doubt, that you should ONLY trust experimental results and not what some "expert" says. (Hint - don't trust us either. Get some metal and try this yourself. It won't insult us .. really.)

By the way, longer rods are easier to resonate than shorter.


This is another experiment several exhibitors had at the 2010 DC Science and Engineering Fair. It is simply a brass bowl, with 2 handles, and partly filled with water. Moving wet hands on the handles causes vibrations. (Wet is important. I think it has a similar effect as rosin.) At resonance, the water jumps out of the bowl. (I need a better video.)

On a serious note, this demonstration indicates that, in some circumstances, water can act as an anti-lubricant. Basically, dry hands do not seem to work, and wet hands do. On the other hand, the water may simply make your skin swell.

In nature, alligators produce low frequency sounds (bellows) that produce a similar result.

Tacoma Narrows Bridge

In architecture, and many engineering projects, resonance is a bad thing. The failure of the Tacoma Narrows Bridge in 1940 is due to resonance when the wind blew across the center span.

Author: Robert Clemenzi
URL: http:// / Resonance.html