law of thermodynamics

American  

noun

1. any of three principles variously stated in equivalent forms, being the principle that the change of energy of a thermodynamic system is equal to the heat transferred minus the work done first law of thermodynamics, the principle that no cyclic process is possible in which heat is absorbed from a reservoir at a single temperature and converted completely into mechanical work second law of thermodynamics, and the principle that it is impossible to reduce the temperature of a system to absolute zero in a finite number of operations third law of thermodynamics.

2. zeroth law of thermodynamics.

---

law of thermodynamics British  

noun

1. any of three principles governing the relationships between different forms of energy. The first law of thermodynamics (law of conservation of energy) states that the change in the internal energy of a system is equal to the sum of the heat added to the system and the work done on it. The second law of thermodynamics states that heat cannot be transferred from a colder to a hotter body within a system without net changes occurring in other bodies within that system; in any irreversible process, entropy always increases. The third law of thermodynamics (Nernst heat theorem) states that it is impossible to reduce the temperature of a system to absolute zero in a finite number of steps

2. Also called: zeroth law of thermodynamics.  the principle that if two bodies are each in thermal equilibrium with a third body then the first two bodies are in thermal equilibrium with each other

---

law of thermodynamics Scientific  

1. See under thermodynamics

---

Example Sentences

The Carnot principle, which later became part of the second law of thermodynamics, was formulated for large-scale systems such as steam turbines.

From Science Daily • Jan. 22, 2026

Speaking at the event on Friday, Ramanna said his system was inspired by the first law of thermodynamics.

From The Wall Street Journal • Nov. 10, 2025

Further studies are necessary before we can definitely state that the second law of infodynamics is as fundamental as the second law of thermodynamics.

From Salon • Oct. 25, 2023

This is a basic law of thermodynamics: heat moves to where it’s colder.

From Seattle Times • Aug. 21, 2023

The second law of thermodynamics results from the fact that there are always many more disordered states than there are ordered ones.

From "A Brief History of Time: And Other Essays" by Stephen Hawking