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Physics vocabulary · Heat and Thermodynamics

Entropy

Meaning in physics, with examples

/ˈentrəpi/nounCommon term

In physics, entropy means: A measure of how spread out, or disordered, the energy of a system is. In an isolated system the total entropy never decreases, which is one way of stating the second law of thermodynamics.

In Turkish: entropi

How it is used

Symbol S, measured in joules per kelvin (J/K). Used to explain why heat flows from hot to cold, why no heat engine can be 100% efficient and why some processes are irreversible. Popular science links it to 'the arrow of time'.

Example sentences

  1. When the ice melts in the warm room, the total entropy of the ice and the room increases.

  2. A refrigerator can lower the entropy inside it only by increasing the entropy of the kitchen.

Common collocations

  • increase in entropy
  • change in entropy
  • second law of thermodynamics
  • entropy of a system
  • first law of thermodynamicsThe principle that the change in a system's internal energy equals the heat supplied to it minus the work it does. It is the conservation of energy applied to heat and work.
  • heatEnergy that flows from a hotter object to a colder one because of the temperature difference between them. Like all energy, it is measured in joules (J).
  • temperatureA measure of how hot or cold something is, linked to the average kinetic energy of its particles. In science it is measured in kelvin (K) or degrees Celsius (°C).
  • efficiencyThe fraction of the energy put into a device that comes out as useful energy. It is given as a decimal or a percentage and can never be more than 100%.
  • heat transferThe movement of thermal energy from a hotter place to a colder one. It happens in three ways: conduction, convection and radiation.

More terms: Heat and Thermodynamics

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