Femtometre

Unit of length in the metric system

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Unit system	Metric
Unit of	Length
Symbol	fm
Named after

A femtometre (fm) is a unit of length in the metric system equal to 1×10⁻¹⁵ metres. It is also known as a fermi, named after the Italian physicist Enrico Fermi. The femtometre is used primarily in particle physics and nuclear physics to measure the size of atomic nuclei and the distances between subatomic particles.

Applications

The femtometre is particularly useful in the field of nuclear physics, where it is used to express the sizes of atomic nuclei. For example, the radius of a proton is approximately 0.84 to 0.87 femtometres. The femtometre is also used in particle physics to describe the range of the strong nuclear force, which is on the order of a few femtometres.

Relation to other units

The femtometre is a submultiple of the metre, the SI base unit of length. It is related to other units of length as follows:

• 1 femtometre = 1×10⁻¹⁵ metres
• 1 femtometre = 1×10⁻¹² micrometres
• 1 femtometre = 1×10⁻⁹ nanometres
• 1 femtometre = 1×10⁻⁶ picometres

History

The term "fermi" was introduced by Enrico Fermi and has been used in the field of nuclear physics since the mid-20th century. The femtometre, as part of the SI, was adopted later to provide a standardized unit of measurement.

See also

• Metre
• Nanometre
• Picometre
• Subatomic particle
• Nuclear physics
• Particle physics