plate glass gravel water sound

I continued with the glass/water/rocks experiments. First I should note a few leftovers that I found when I returned to my assemblage.

When the water evaporated, a powdery deposit remained.

This substance was chalky and did not hold together well but left some interesting patterns, particularly on the stones themselves.

I left what silt was in the glass, then prepared to try an experiment to the previous with plate glass instead of a goblet. The assemblage:

-Scrap of plate glass

-Gravel from previous (silt washed off)

-Small container of water to wet rocks

-Hammer (for just in case)

Similar to the previous iteration, I held the glass with the rocks and water on top and agitated laterally. The glass, being flat did not hold the rocks well. 

Notably the individual rocks did not move uniformly. Some moved greater distances when agitated and some appeared to move more in certain directions than others. A whole mess of research could be done on the effects of shape size and mass on movement in these circumstances. 

I however was in no mood for analysis or physics. Instead I decided to try a different approach and decided to try to get the plate to resonate with the rocks on top.

When I was researching resonance the other day I came across forms know as Chlandi patterns. If the rocks one uses are small enough (say sand) and placed upon a vibrating plate with free edges, they will form regular patterns dependent upon the mode of harmonic excitation of the system. 

Chlandi patterns:

from “The Physics of Sound” by Berg and Stork

I figured I would try for something more like this, and that it was OK to continue using the gravel because the results for sand are already known

I slid the plate so that most of it hung off the edge of the desk and placed my backpack on it so that the plate would not fall off.

I attempted to make the plate resonate by tapping with a finger and a pencil. I was not satisfied with the results. I remembered a description of a Chlandi apparatus where the plate was driven from a central string which itsself was excited by musical bow. I didn't have one nor a way to get a string through the center of the glass but I looked around for something similar. I found some thin plastic tubing. This I drew along the edge f the glass farthest from the desk.

This made some interesting noise and left behind some cool shavings

 I also spotted a flue brush with a handle made of twisted wire - I tried this on the edge. It was much better at creating vibrations - the texture of the tightly twisted wire seems to do a very good job of 'grabbing' the edge of the glass just right.

Note that this quickly erodes the sharp edge of the glass. This is potentially very useful! I don't know of any other way to do this besides expensive diamond grit abrasives. Also if done in a more controlled manner it appears as though this would begin to cut the glass like a saw (certain types of PVC saw work in this way). This also leaves behind a fine dust of metal and glass.

The really interesting stuff happened though when I tried to record the sounds. I will play them in class because I haven't figured out how to do that here and also I think the real breakthrough one will have a cool effect over Skype.