chaleur

Chaleur is the French word for heat and, in everyday language, warmth. In physics, chaleur (heat) is the form of energy transferred between systems or bodies due to a temperature difference. It is not a substance, but energy in transit. Temperature, by contrast, is a measure of the average kinetic energy of particles and does not itself denote energy transfer.

Heat can be transferred by three mechanisms: conduction, convection, and radiation. Conduction occurs through direct contact between substances; convection involves bulk motion of fluids; radiation transfers energy as electromagnetic waves. The amount of heat transferred is measured in joules in the SI system; the calorie is a historical unit often used in food energy.

In many materials, the relation between heat and temperature change is governed by the specific heat capacity, c, through Q = m c ΔT for a mass m. When a substance changes phase, heat is required or released without a change in temperature; this latent heat is quantified as Lf for fusion and Lv for vaporization.

Thermodynamics describes heat within energy balance. The first law states that the change in internal energy equals heat added minus work done by the system (ΔU = Q − W). Practical studies of chaleur underpin heat engines, refrigeration, climate science, cooking, and many industrial processes.

Historically, the concept of heat evolved in the 18th and 19th centuries, with contributions from scientists such as Cavendish, Joule, Carnot, and Clausius, leading to the development of the mechanical theory of heat and the idea of entropy.