Joule

The joule is the SI unit of energy, and is the energy which will sustain a force of one newton over one metre. The symbol of the joule in SI is J. The joule is also used to measure thermal energy, and is the unit of work. The joule is also the energy produced by a source of power of one watt in one second, and the energy released by an electric charge of one coulomb dropping one volt in electrical potential.

The joule is named for James Prescott Joule (1818 - 1889), who discovered the relation between mechanical and heat energy.

The joule is a derived unit in the SI, equal to 1 N·m; or in terms of SI basic units: J = m²·kg·s^-2.

Practical use

• A baseball pitched by a fast Major League pitcher has a kinetic energy of approximately 230 J.
• One "dietary calorie" (as used in the United States) is 4186 J (4.186 kJ).
• One gram of gasoline releases about 50 kJ on combustion in air.
• A small car (about 1200 kg) travelling at 65 miles per hour (105 km/h) has a kinetic energy of 1 megajoule (1 MJ).
• One "kilowatt-hour" is 3.6 MJ.
• One ton of TNT releases 4.184 GJ on exploding.