Editing Coin (section)

== Physics and chemistry ==
[[File:2019 American Silver Eagle and 1943 Walking Liberty Half dollar side by side.jpg|thumb|right|An [[American Silver Eagle]] minted in 2019 (left), an example of a [[Bullion coin]]. Its obverse design is based on the older, formerly circulating silver [[Walking Liberty half dollar]] (right).]]

=== Flipping ===
{{Main|Coin flipping}}
To flip a coin to see whether it lands ''heads'' or ''tails'' is to use it as a two-sided [[dice|die]] in what is known in mathematics as a [[Bernoulli trial]]: if the probability of heads (in the parlance of Bernoulli trials, a "success") is exactly 0.5, the coin is fair.

=== Spinning ===
{{further|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.<ref>{{Cite journal|last1=Easwar |first1=K. |last2=Rouyer |first2=F. |last3=Menon |first3=N. |title=Speeding to a stop: The finite-time singularity of a spinning disk |doi=10.1103/PhysRevE.66.045102 |journal=Physical Review E |volume=66 |issue=4 |pages=045102 |year=2002 |pmid=12443243 |bibcode=2002PhRvE..66d5102E }}</ref>

===Odor===
Iron and copper coins have a characteristic metallic smell that is produced upon contact with oils in the skin. Perspiration is chemically reduced upon contact with these metals, which causes the skin oils to decompose, forming with iron the volatile molecule [[1-octen-3-one]].<ref>[http://www.nature.com/news/2006/061023/full/news061023-7.html A 'metallic' smell is just body odour] {{webarchive|url=https://web.archive.org/web/20160524004703/http://www.nature.com/news/2006/061023/full/news061023-7.html |date=2016-05-24 }}</ref>