In the field of atomic and molecular physics, an "atomic unit of length" is a unit of measurement that is used to express distances at the atomic and molecular scale in a dimensionless way. It is part of a system of atomic units (a.u.) that simplifies calculations involving fundamental physical constants and properties of atoms and molecules.
The atomic unit of length (a.u. of length) is defined in terms of the Bohr radius (a₀), which is a fundamental constant in atomic physics. The Bohr radius is approximately 0.52917721067 angstroms (Å) or 5.2917721067 x 10^-11 meters (m).
In atomic units, the Bohr radius is set to exactly 1 a.u. of length. Therefore, when using atomic units, distances are expressed relative to the Bohr radius, and the value of 1 a.u. of length corresponds to the typical size scale of atomic and molecular structures.
The use of atomic units simplifies many quantum mechanical calculations and allows physicists and chemists to work with dimensionless quantities, making it easier to compare and analyze atomic and molecular properties.
A furlong is a unit of length that is used primarily in horse racing and some other sports, as well as in some older systems of measurement. In modern terms, one furlong is equal to 1/8th of a mile. This is equivalent to 660 feet or 220 yards.
The term "furlong" has historical roots and was originally used in medieval England as a way to measure distances for plowing fields. Over time, it became associated with horse racing and is still used today to describe the length of a horse racing track. In horse racing, races are often measured in furlongs, and the distance of a race may be referred to as "6 furlongs" or "10 furlongs," for example.
While the furlong is not commonly used in everyday measurements, it is still relevant in certain specialized contexts, particularly in horse racing and related sports.