Definition: As a physical quantity, energy designates the ability of a physical system to perform work, release heat or emit radiation. Energy occurs in different forms. Examples are kinetic, electric, chemical, and thermal energy. The forms of energy can be converted. Hence, a steam turbine converts the different energy forms of water vapor into electrical energy. The fundamental importance of energy is reflected in every science and in business. It is measured depending on the type of energy:
- thermal energy in Joule (J),
- mechanical energy in Newton metre (Nm), and
- electrical energy in watt-seconds (Ws).