Wärme

Wärme is the energy transfer between bodies or systems as a result of a temperature difference. It is not a property of a material but energy in transit; the amount transferred depends on the process and the properties of the substances involved. In thermodynamics, heat is measured in joules, with common smaller units such as calories (1 cal = 4.184 J).

The amount of heat required to raise the temperature of a substance depends on its mass, its specific heat capacity, and the temperature change, described by Q = m c ΔT for sensible heat. When a substance changes phase, additional heat, called latent heat, is involved, such as the latent heats of fusion and vaporization.

Heat transfer occurs mainly through three mechanisms: conduction, convection, and radiation. Conduction involves energy transfer through solids and dense fluids via molecular interactions; metals are particularly good conductors. Convection involves the bulk movement of fluids, as warm air rising or boiling water circulating. Radiation transfers energy by electromagnetic waves and does not require a material medium, allowing the Sun to warm the Earth.

In everyday and technical contexts, Wärme is central to heating and cooling systems, engines, climate processes, and many biological and chemical phenomena. The concept contrasts with temperature, which is a measure of the average kinetic energy of particles within a body; heat is the energy in transit that can change that energy or cause phase transitions.