A "fermi" (symbol: fm) is a unit of length used in physics to describe extremely small distances at the atomic and subatomic scale. One fermi is equal to 10^-15 meters or 0.000000000000001 meters. It is named after the Italian physicist Enrico Fermi, who made significant contributions to nuclear physics and particle physics.
The fermi is particularly useful for describing the sizes of atomic nuclei and the distances between particles within atomic nuclei. For example, the typical diameter of an atomic nucleus is on the order of a few femtometers (1 femtometer = 1 fm). It is also used in high-energy particle physics to describe the cross-sectional area of particle interactions.
In summary, the fermi is an essential unit of length for understanding the microscopic world of atoms, nuclei, and subatomic particles, where distances are incredibly small.
An "ell" is an antiquated unit of length that has been historically used in various countries, including England, Scotland, and Germany. The length of an ell could vary depending on the region and the specific purpose, but it was typically used to measure cloth or textiles. The term "ell" is derived from the Latin word "ulna," which means "forearm," as the length of an ell was often based on the length of a person's forearm.
Different regions had their own variations of the ell, but some common measurements include:
English Ell: In England, the English ell was approximately 45 inches or 1.143 meters.
Scottish Ell: In Scotland, the Scottish ell was longer, measuring around 37 inches or 0.94 meters.
French Ell: In France, the French ell, also known as the aune, was used and had its own variations, but it was typically around 1.188 meters.
Flemish Ell: In parts of Europe, including Belgium and the Netherlands, the Flemish ell was used, which was approximately 27 inches or 0.686 meters.