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ther·mo·dy·nam·ics (thûrmō-dī-nămĭks)
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n.
1. (used with a sing. verb) Physics that deals with the relationships and conversions between heat and other forms of energy.
2. (used with a pl. verb) Thermodynamic phenomena and processes.

THERMODYNAMICS

Thermodynamics is the branch of physics that deals with the relationships between heat and other forms of energy. Four basic laws have been established.

THE FOUR LAWS
First LawThe first law states that the amount of energy added to a system is equal to the sum of its increase in heat energy and the work done on the system. The first law is an example of the principle of conservation of energy.
Second LawThe second law states that heat energy cannot be transferred from a body at a lower temperature to a body at a higher one without the addition of energy. Thus, warm air outside can transfer its energy to a cold room, but transferring energy from a cold room to the warm air outside requires extra energy (as with an air conditioner).
Third LawThe third law states that the entropy of a pure crystal at absolute zero is zero. Since there can be no physical system with lower entropy, all entropy thus has a positive value by definition.
Zeroth LawThe zeroth law states that if two bodies are in thermal equilibrium with some third body, then they are also in equilibrium with each other. This law has its name because it was implicitly assumed in the development of the other laws, and is in fact more fundamental than the others, but was only later established as a law itself.

Copyright © 2011 by Houghton Mifflin Harcourt Publishing Company


The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2019 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
 

Indo-European & Semitic Roots Appendices

    Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:

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    The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.

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