Joule (J)

Definition

The joule (J) is the SI unit of energy, work, and heat. It is defined as the amount of energy transferred when a force of one newton moves an object one meter in the direction of the force. Formally, 1 J = 1 N·m = 1 kg·m²/s².

History

The joule is named after the British physicist James Prescott Joule, who studied the relationship between heat and mechanical work in the 19th century. The term "joule" was officially adopted in 1889 at the first International Electrical Congress, recognizing Joule's contributions to thermodynamics and energy.

Uses

Joules are widely used in physics and engineering to quantify energy, work, and heat. In everyday life, you might encounter joules in contexts such as electrical energy consumption (e.g., kilojoules in food energy). The unit is standard in scientific research globally, particularly in fields like thermodynamics and mechanics.

Conversions

• 1 J = 0.239 calories (cal)
• 1 J = 1 × 10⁻³ kilojoules (kJ)
• 1 J = 0.737 foot-pounds (ft·lb)

Fun Facts

• A common misconception is that joules only measure electrical energy; they apply to all forms of energy.
• The joule is also used to express energy in various contexts, such as calories in nutrition.