Spectrum Analysis Of Ring Test Of 50% And 80% 1967 Coins - Page 2

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Scooby Due Pillar of the Community United States 4000 Posts	Posted 01/24/2011 9:43 pm Very interesting read. Thank you! How about some '82 zinc vs. copper comparisons. Report this Post to the Staff
sel_69l Bedrock of the Community Australia 21788 Posts	Posted 01/25/2011 06:27 am samboyyellowsub:That's interesting. Australia used to have sliver florin coins in circulation prior to the introduction of decimal currency in 1966. Coins made before 1946 were .925 fine, those after that were .500 fine, but had the same mass and diameter. The alloys for .925 fine were silver 92.5%, copper 7.5%, and for .500 fine were silver 50%, copper 40%, nickel 5%, and zinc5% That means the .925 silver coins were thinner and denser that the .500 ones. This resulted in the two alloys having different ring tones, naturally. The ring pitch of the .925 coins is lower. I had always assumed that due to greater inertia resulting from the greater density of the .925 coins, the ring tones for for these coins must be lower. I guess that if you have clad coins rather than a homogeneous alloy, the ring characteristics would be altered in a different way than by the assumption that I have indicated above. Although my observations are true, my assumptions may be wrong. Can you make a comment about my assumptions? Report this Post to the Staff
samboyellowsub Valued Member United States 113 Posts	Posted 01/25/2011 09:40 am sel_691, If the mass is the same, actually, the inertia is the same. Although, I get what you're thinking about density affecting inertia. Say you have an inflated birthday party balloon, and a coin that is the same mass. What you're perceiving is that the coin has greater inertia for its size, than the balloon, which it true. But they have the same inertia if they have the same mass. In two similarly sized objects, the thing that affects the pitch the most is not necessarily the density, but the speed of sound in the material. Copper is less dense than silver but carries sound (mechanical vibrations) faster than silver in all respects. This is not always the rule though. For instance tungsten is nearly twice as dense as silver, and it carries sound much faster than silver. The speed of sound is proportional to a material's elasticity. An easily perceptible mechanical property related to elasticity is probably malleability versus springiness, the easier a metal "gives" without the tendency to return to its undisturbed state, the lower its elasticity and the lower the speed of sound and the lower the ring pitch. Like gold, it is softer than silver and as you might expect it carries sound slower. Hope that helps. Report this Post to the Staff
samboyellowsub Valued Member United States 113 Posts	Posted 01/25/2011 09:45 am forgot to add, that yes, a clad coin will change things quite a bit. The chunk of zinc inside the penny will act almost completely independently of the copper cladding. The reason for this is that there is a boundary between the copper and zinc and sound reflects off of boundaries in materials. Not to say that some sound doesn't transmit between boundaries, because it does. But that is why it doesn't sound as sharp, because its two resonant systems; the filler and the cladding and they do compete with each other for sonic real-estate! Report this Post to the Staff
North of 49 Pillar of the Community Canada 617 Posts	Posted 01/25/2011 6:40 pm Very impressive , thanks. Report this Post to the Staff
sel_69l Bedrock of the Community Australia 21788 Posts	Posted 01/25/2011 11:44 pm samboyellowsub. Before, I did not have enough background knowledge. Now I have a reason. It seems that the lattice structure of atoms in a metal or an alloy has a lot to do with elasticity and sound transmission. Some alloys are certainly harder, and that is why alloys are preferred to pure metals in circulating coins. Sukria. ('thankyou' in Urdu)! Report this Post to the Staff
SPP-Ottawa Moderator Canada 10463 Posts	Posted 11/23/2011 9:42 pm Quote: I dropped the coins on my hardwood floor on which I rested my laptop I would like to see a repeat of your test, but with the coins dropped on a piece of marble. That is what the Royal Canadian Mint used to use to "ring" their silver coins, 'odd' sounding coins were rejected, which could have been a bad alloy mix of silver, or other flaws like cracked coins. http://www.liveleak.com/view?i=677_1293705960 (you can fast forward to 8:03 of this archive video) Also, that is why vintage cash registers also used to have a marble slab above the cash drawer, to ring the coins if they were suspect of being a cast counterfeit of other metals or lower silver content. "Discovery follows discovery, each both raising and answering questions, each ending a long search, and each providing the new instruments for a new search." -- J. Robert Oppenheimer Content of this post is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported License. See: http://creativecommons.org/licenses...0/deed.en_US My eBay store Edited by SPP-Ottawa 11/23/2011 9:46 pm Report this Post to the Staff
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