A meter (m) is the base unit of length in the International System of Units (SI), which is the modern metric system used for scientific and everyday measurements in most countries around the world. The meter is defined as the length of the path traveled by light in a vacuum during a time interval of 1/299,792,458 of a second.
In more practical terms, a meter is approximately equal to:
Meters are commonly used for measuring various lengths and distances, including the dimensions of objects, the length of rooms or buildings, and distances between locations on Earth. It is a versatile unit of measurement that is widely used in science, engineering, construction, and everyday life.
A femtometer (fm), also known as a fermi, is an extremely tiny unit of measurement used to express even smaller distances than a picometer. It is equal to one quadrillionth of a meter, which is 0.000000000000001 meters or 1 × 10^-15 meters. The prefix "femto" denotes a factor of 10^-15 in the International System of Units (SI).
Femtometers are typically used in the field of nuclear physics and particle physics to describe the sizes and distances involved in atomic nuclei and subatomic particles. The nucleus of an atom, for example, is on the order of a few femtometers in diameter. In high-energy physics experiments and discussions about fundamental particles like protons, neutrons, and quarks, femtometers are a relevant unit of measurement due to the incredibly small scales involved.