Definition

Noun: A fundamental principle of physics stating that the total entropy of an isolated system can never decrease over time. It describes the irreversibility of natural processes, indicating that energy spontaneously disperses from being concentrated to becoming more spread out and that heat flows naturally from hotter to colder objects.

Usage

The "second law of thermodynamics" is used to explain why certain processes are irreversible and to define the direction of time for thermodynamic systems. - It is a cornerstone of classical thermodynamics and statistical mechanics. - It is often invoked in discussions about energy efficiency, heat engines, and the ultimate fate of the universe.

Examples

• Scientific Context:
  • The second law of thermodynamics explains why a cup of hot coffee left on a table eventually cools to room temperature.
  • According to the second law of thermodynamics, no heat engine can be 100 percent efficient because some energy is always dissipated as waste heat.
• Broader Context:
  • The concept of entropy increase from the second law of thermodynamics is sometimes used metaphorically to describe increasing disorder in complex systems.

Advanced Usage

• Clausius Statement: "Heat can never pass from a colder to a warmer body without some other change, connected therewith, occurring at the same time." This is one formulation of the law.
• Kelvin-Planck Statement: "It is impossible to devise a cyclically operating device which produces no other effect than the extraction of heat from a single body and the performance of an equivalent amount of work." This is another equivalent formulation focusing on heat engines.

Variants and Related Words

• Entropy (n): A measure of the disorder or randomness in a system, central to the statement of the second law.
• Thermodynamics (n): The branch of physics that deals with the relationships between heat and other forms of energy.
• First Law of Thermodynamics (n): The law of conservation of energy for thermodynamic systems.
• Third Law of Thermodynamics (n): The law stating that the entropy of a perfect crystal approaches zero as the temperature approaches absolute zero.

Synonyms

• Law of increased entropy
• Entropy principle

Related Phrases

• Heat death of the universe: A hypothesized ultimate fate of the universe, derived from the implications of the second law, where maximum entropy is reached and no thermodynamic free energy remains.
• Perpetual motion machine of the second kind: A hypothetical machine that violates the Kelvin-Planck statement of the second law by converting heat entirely into work.

Noun

1. a law stating that mechanical work can be derived from a body only when that body interacts with another at a lower temperature; any spontaneous process results in an increase of entropy