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Law VS Principle VS Theory

  1. Nov 9, 2013 #1


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    I tried to google it, but I got much more confused with different and contradictory definitions. Can somebody please help me understand the difference between these terms? Is there overlapping between them? Some books say "Law of conservation of energy", but others say "Principle of conservation of energy", which is more accurate?

    Thanks in advance.
  2. jcsd
  3. Nov 9, 2013 #2


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    A principle is something that you have to apply to the problem; it is not an equation.

    Thus Fermat's principle, the principle of conservation of energy, etc.

    A law is usually some empirical statement - "Kepler's Laws of Planetary Motion", but not always.

    The terminology is often inconsistent.
  4. Nov 9, 2013 #3


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    Historically, "laws of physics" tended to be things that were experimentally true, but at the time there was no deeper explanation for them. Examples: Hooke's law of elasticity, Boyle's and Charles's gas laws, Snell's law of refraction, Faraday's and Lenz's laws of electromagnetic induction, etc.

    Later, those laws became absorbed into more general bodies of knowledge - e.g. solid mechanics, thermodynamics of an ideal gas, EM theory, etc, but the original names remain, in memory of their discoverers.
  5. Nov 9, 2013 #4


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    Staff: Mentor

    Since this is a science forum, the scientific definition would apply




    Last edited: Nov 9, 2013
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