femtometër

The femtometre, also known as the fermi, is a unit of length in the metric system, equal to 10^-15 meters or one quadrillionth of a meter. It is commonly used in the fields of particle physics and nuclear physics to describe the extremely small scales at which these phenomena occur. The term "femto" is derived from the Danish and Norwegian word "femten," meaning fifteen, reflecting the unit's origin as a subdivision of the ångström, which was defined as 10^-10 meters. The femtometre is abbreviated as "fm." For example, the diameter of a proton is approximately 1.7 fm. The femtometre is part of the International System of Units (SI), and its use is standardized by the International Bureau of Weights and Measures.