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Circulating coins commonly suffered from "shaving" or "clipping": the public would cut off small amounts of precious metal from their edges to form new coins.[29] Unmilled British sterling silver coins were sometimes reduced to almost half their minted weight. This form of debasement in Tudor England was commented on by Sir Thomas Gresham, whose name was later attached to Gresham's law. The monarch would have to periodically recall circulating coins, paying only the bullion value of the silver, and reminting them. This, also known as recoinage, is a long and difficult process that was done only occasionally.[30] Many coins have milled or reeded edges, originally designed to make it easier to detect clipping. The side of a coin carrying an image of a monarch or other authority, or a national emblem, is usually called the obverse, or colloquially, heads; see also List of people on coins. The other side, which may carry the denomination, is usually called the reverse, or colloquially, tails. The year of minting is usually shown on the obverse, although some Chinese coins, most Canadian coins, the pre-2008 British 20p coin, and all Japanese coins, are exceptions. In cases where a correctly oriented coin is flipped about its horizontal axis to show the other side correctly oriented, the coin is said to have coin orientation. In cases where a coin is flipped about its vertical axis to show the other side correctly oriented, it is said to have medallic orientation. While coins of the United States dollar display coin orientation, those of the Euro and pound sterling have medallic orientation. Bimetallic coins are sometimes used for higher values and for commemorative purposes. In the 1990s, France used a tri-metallic coin. Common circulating bimetallic examples include the €1, €2, British £2 and Canadian $2. The exergue is the space on a coin beneath the main design, often used to show the coin's date, although it is sometimes left blank or containing a mint mark, privy mark, or some other decorative or informative design feature. Many coins do not have an exergue at all, especially those with few or no legends, such as the Victorian bun penny. 3 Russian Rubles coin minted in 2008. Not all coins are round. The Australian 50 cent coin, for example, has twelve flat sides. Some coins have wavy edges, e.g. the $2 and 20-cent coins of Hong Kong and the 10 cent coins of Bahamas. Some are square-shaped, such as the 15 cent coin of the Bahamas. During the 1970s, Swazi coins were minted in several shapes, including squares, polygons, and wavy edged circles with 8 and 12 waves. Some other coins, like the British 20 and 50 pence coins and the Canadian Loonie, have an odd number of sides, with the edges rounded off. This way the coin has a constant diameter, recognisable by vending machines whichever direction it is inserted. A triangular coin with a face value of £5 (produced to commemorate the 2007/2008 Tutankhamun exhibition at The O2 Arena) was commissioned by the Isle of Man: it became legal tender on 6 December 2007.[31] Other triangular coins issued earlier include: Cabinda coin, Bermuda coin, 2 Dollar Cook Islands 1992 triangular coin, Uganda Millennium Coin and Polish Sterling-Silver 10-Zloty Coin.[32] Guitar-shaped coins were once issued in Somalia. Poland once issued a fan-shaped 10 złoty coin and the 2002 $10 coin from Nauru, was Europe-shaped.[33] Some mediaeval coins, called bracteates, were so thin they were struck on only one side. The Royal Canadian Mint is now able to produce holographic-effect gold and silver coinage. However this procedure is not limited to only bullion or commemorative coinage. The 500 yen coin from Japan was subject to a massive amount of counterfeiting. The Japanese government in response produced a circulatory coin with a holographic image. The Royal Canadian Mint has also released several coins that are coloured, the first of which was in commemoration of Remembrance Day. The subject was a coloured poppy on the reverse of a 25 cent piece. For a list of many pure metallic elements and their alloys which have been used in actual circulation coins and for trial experiments, see coinage metals.[34] Physics Flipping Main article: Coin flipping Coins are popularly used as a sort of two-sided die; in order to choose between two options with a random possibility, one choice will be labeled heads and the other tails, and a coin will be flipped or tossed to see whether the heads or tails side comes up on top – see coin flipping. Mathematically, this is known as a Bernoulli trial: a fair coin is defined to have the probability of heads (in the parlance of Bernoulli trials, a "success") of exactly 0.5. Spinning Further information: Euler's Disk Coins can also be spun on a flat surface such as a table. This results in the following phenomenon: as the coin falls over and rolls on its edge, it spins faster and faster (formally, the precession rate of the symmetry axis of the coin, i.e., the axis passing from one face of the coin to the other) before coming to an abrupt stop. This is mathematically modeled as a finite-time singularity – the precession rate is accelerating to infinity, before it suddenly stops, and has been studied using high speed photography and devices such as Euler's Disk. The slowing down is predominantly caused by rolling friction (air resistance is minor), and the singularity (divergence of the precession rate) can be modeled as a power law with exponent approximately −1/3.[35] Chemistry The odor of coins Iron coins have a characteristic metallic smell that is produced upon contact with oils in the skin. Perspiration is chemically reduced upon contact with iron, which causes the skin oils to decompose, forming the volatile molecule 1-octen-2-one.[36] |
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