Kilogram-force (kgf)
The kilogram-force, symbol kgf, defines a non-SI unit as the force Earth’s gravity exerts on one kilogram of mass at sea level, equal to 9.80665 newtons. Engineers and mechanics widely used it before the universal adoption of the SI. Today, users still find kilogram-force in older engineering documents, aviation, and certain regions. Its continued presence shows how mass-based and force-based units overlap, highlighting the transition from practical everyday measurements to the universal SI system.
Dyne (dyn)
The dyne (dyn) is a force unit in the centimeter–gram–second (CGS) system. It was common in 19th and early 20th-century physics. One dyne equals 10⁻⁵ newtons. It is the force needed to accelerate a mass of one gram by one centimeter per second squared. Today, science uses the newton, but dynes are still used in specialized fields, such as measuring surface tension in chemistry and physics. The dyne helped bridge old metric units with today’s SI.