It is not an SI unit because it contains the non-SI unit hour. Rapid advances in science and technology in the 19th and 20th centuries. Table Showing Some Common Derived Quantities And Their Si Units Basic Physics Physics Notes Physics Formulas Although SI is used almost universally in science including in the US some countries such as the United States still use their own system of units. . The site also includes a predictive tool that suggests possible conversions based on input allowing for easier navigation while learning more about various unit systems. The SI unit of energy is the joule J equal to one watt-second. Adopted by the 11th General Conference on Weights and Measures CGPM in 1960 it is abbreviated SI in all languages. Thus the names of all units start with a lower-case letter except at the beginning of a sentence or in capitalized material such as a title. International System of Units SI French Système Inte