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Q: Sound in crystal water glass ( Answered ,   3 Comments )
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 Subject: Sound in crystal water glass Category: Science > Physics Asked by: taxingwoman-ga List Price: \$5.00 Posted: 03 Feb 2003 15:51 PST Expires: 05 Mar 2003 15:51 PST Question ID: 156934
 ```How is sound created in a crystal water glass when you rub the edge. A picture would be good.```
 Subject: Re: Sound in crystal water glass Answered By: ericynot-ga on 03 Feb 2003 20:39 PST Rated:
 ```Hi taxingwoman, Your question brought back memories of past family holiday dinners when the siblings and I would endeavor to play various songs on Mom's best wine glasses. We had a lot of fun, and somehow managed not to ever break any of them :) So, what made those impromptu performances possible? In a word, friction. From the "Apple Valley High School Physics Web Page" we learn this: "Question: What causes the glass to sing when your finger goes around the rim? The ridges in your finger set the glass into vibration at its natural frequency. These vibrations build and form a loud sound. Question: Does your fingertip need to be wet? What does the moisture have to do with anything? Your fingertip needs to be wet in order to remove the oils from between your finger's ridges. This helps produce just the right amount of friction between your fingertip and the glass." http://www.isd196.k12.mn.us/Schools/avhs/AV%20connect/science/sound-notes.html Here's a slightly more detailed explanation from the How Stuff Works website: "Every material (such as glass, steel, concrete) has a natural frequency at which it vibrates, called a resonant frequency. If you put energy into the substance at its resonant frequency, you will force it to vibrate or resonate (resonance is a forced vibration). In the case of the wine glass, your finger slides and sticks along the surface of the glass as you rub the rim (a wet fingertip has no oil and makes a better contact with the glass). The rubbing imparts energy to the glass molecules and causes them to resonate. The motion of your hand sets up a wave of vibration traveling through the glass. The vibrating glass causes air molecules to vibrate at the same frequency. The vibrating air molecules are the sound wave that you hear (the frequency or pitch of the sound wave is the same as the resonant frequency of the glass). So, how does the water change the pitch of the singing wine glass? As the resonant wave moves around the glass, it drags the water molecules with it, creating a wave of water that you can see near the edge of the glass. The dragging water molecules effectively increase the mass (both the water and the glass molecules) and reduce the energy of the wave traveling through the glass. When the energy is reduced, so is the frequency of the wave in the glass, which is reflected in the pitch of the sound wave that you hear." http://science.howstuffworks.com/question603.htm Those explanations are educational, but they leave unanswered a nagging question: why don't regular glasses make music like the good crystal? Here's an enlightening discussion of that question from "How Things Work" by Lou Bloomfield: What is the difference between crystal and glass? "The 'crystal' that's used in fine glassware is actually a glass, but it is chemically different from the glass that's used in more common glassware. Both materials are formed by melting together a mixture of silicon dioxide (also called quartz or silica) and other chemicals and both are glasses, meaning that their atoms are arranged haphazardly and not in the crystalline lattices of such materials as salt or sugar. But the chemicals that are added to silicon dioxide to make normal glassware--sodium oxide and calcium oxide--make the glass easier to melt and work with at the expense of strength. That's why normal glassware is relatively soft, emitting a dull sound when you rap it because it experiences lots of internal friction. In contrast, the chemicals added to silicon dioxide to make "crystal" glassware include lead oxide, which makes the glass easier to melt but doesn't weaken the glass nearly so much. Lead "crystal" glassware is relatively hard and emits a ringing tone when you rap it because it experiences very little internal friction." http://howthingswork.virginia.edu/windows_and_glass.html You asked about a picture, but this is a discussion of an action event, so here's a video showing how to make a wine glass "sing": http://science.howstuffworks.com/mpeg/wine.mpg One more thing: in researching your question, I learned that Benjamin Franklin, back in 1761, designed a musical instrument using these principles which he called the Armonica. Unfortunately, Franklin's instrument was made of lead glass which evidently caused neurologic damage to many of those who played it. In 1982, an inventor named Gerhard Finkenbeiner successfully recreated Franklin's armonica (thankfully) using lead-free glass. You can learn more about this instrument here: http://www.crystalmusic.com/glassarmonica.html If you have any questions about this answer, just use the Answer Clarification feature before rating it, and I'll get right back to you. Thanks for your very interesting question, ericynot-ga Google search term: crystal glass sound explanation```
 taxingwoman-ga rated this answer: ```Wow ! How nice to have a clear answer to my question. Thanks for all the links,very helpful```

 ```As an inveterate singing wine glass performer, I would like to add that glass other than lead crystal can be made to resonate. It only need be thin enough. The section of the answer that referred to a glass harmonica made with unleaded glass proves the point. By the way, the part about lead crystal glass harmonicas causing health problems is nonsense, typical of the hysteria caused by those who haven't a clue about relative exposure to toxic materials. I am a retired chemist who worked in the coatings (paint) industry. I inhaled and handled more lead pigment in my 45 years in the business than 100 average persons are likely to encounter in their lifetimes. I am 75 years old and probably in better health than the neurotics who believe we are all doomed by whatever their current bogeyman may be.```
 `Didn't the Romans all go crazy from drinking out of lead cups ?`
 ```Taxingwoman-ga asks if the "Romans *all* went crazy from drinking out of lead cups". The short answer is NO, as in NO. There is plausible conjecture that lead poisoning may have been endemic in parts of the Roman Empire because of their use of lead plumbing. Since the Roman regime persisted for 500 years and produced hundreds of brilliant and effective personages, it is, to put it charitably, obvious that not *all* Romans were crazy. As for today's lead hazards: children eating lead paint chips, definitely; exhaust from engines using leaded gas, maybe, but how much leaded gas is used in US today?;drinking from leaded crystal, miniscule. My family and friends who dine with us have been using leaded crystal glassware for 45 years. We may be crazy, but not because of lead.```