calor

Calor is a term that can refer to several related concepts. In everyday Spanish and other Romance languages, calor means heat or warmth and is used to describe high temperatures, a sensation of being hot, or the warmth of objects and environments. In scientific contexts written in Spanish, calor equals thermodynamic heat—the form of energy that flows between systems as a result of a temperature difference.

Caloric theory: In the history of physics, calor or caloric was a hypothetical, weightless fluid proposed to be the fundamental cause of heat. The theory posited that caloric was conserved and could move from hotter to colder bodies, accounting for thermal phenomena. It gained prominence in the 18th century through the work of Antoine Lavoisier and others, but was gradually challenged by experiments showing heat can be produced by work. Experiments by Count Rumford (Benjamin Thompson) and especially James Prescott Joule demonstrated the equivalence of heat and work, leading to the abandonment of caloric in favor of caloric-less, kinetic theories of heat and the first law of thermodynamics.

Contemporary usage: Today, caloric theory is treated as a historical concept. In physics and engineering, heat is described in terms of internal energy, temperature, and entropy; calor is not considered a real substance. The term "calor" persists in linguistic usage as the Spanish word for heat and in some technical terms borrowed from Spanish, but it no longer denotes a physical fluid.