Joule

Joule

Diagram illustrating the definition of a joule.

The joule (symbol: J) is the SI unit of energy, work, or amount of heat. It is named after the English physicist James Prescott Joule. One joule is defined as the amount of energy transferred when a force of one newton is applied over a distance of one meter.

Definition

The joule is defined as:

1 J = 1 N·m = 1 kg·m_/s_

This means that one joule is equivalent to one newton of force causing a displacement of one meter. It can also be expressed in terms of other SI base units as one kilogram meter squared per second squared.

Applications

The joule is used in various fields of science and engineering to quantify energy, work, and heat. It is commonly used in physics to describe the energy of moving objects, in thermodynamics to measure heat transfer, and in electrical engineering to quantify electrical energy.

Related Units

The joule is related to other units of energy, such as the calorie, electronvolt, and watt-hour.

• 1 calorie ≈ 4.184 J
• 1 electronvolt (eV) ≈ 1.602 _ 10___ J
• 1 watt-hour (Wh) = 3600 J

Historical Context

The joule is named after James Prescott Joule, who studied the nature of heat and discovered its relationship to mechanical work, leading to the formulation of the first law of thermodynamics. His experiments in the 1840s established the mechanical equivalent of heat, which laid the foundation for the concept of energy conservation.

See Also

• Energy conservation
• First law of thermodynamics
• Newton (unit)
• Watt

Related Pages

• James Prescott Joule
• SI base units
• Thermodynamics