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Glossary
Joule
A joule (symbol J) is the SI unit of energy—used for mechanical work, heat, and energy in general. It tells you “how much energy was transferred or required.”
On one line: 1 J = 1 N·m (one newton of force applied through one meter of distance). It’s also equal to 1 watt-second (1 W·s), which is handy in electrical and thermal work.
Industrial intuition: a joule is pretty small, so you’ll often see kJ or MJ. For example, tightening a fastener, accelerating a rotating shaft, heating a small volume of fluid, or absorbing impact energy in a test can all be expressed in joules—but larger systems (steam, furnaces, engines) quickly move into kilojoules and megajoules.