What Are the Differences Between Law, Principle, and Theory in Science?

[bgq]

Hi,

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.

 

[UltrafastPED]

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.

 

[AlephZero]

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.

 

[Evo]

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

Theory

Definitions from scientific organizations
The United States National Academy of Sciences defines scientific theories as follows:
The formal scientific definition of theory is quite different from the everyday meaning of the word. It refers to a comprehensive explanation of some aspect of nature that is supported by a vast body of evidence. Many scientific theories are so well established that no new evidence is likely to alter them substantially. For example, no new evidence will demonstrate that the Earth does not orbit around the sun (heliocentric theory), or that living things are not made of cells (cell theory), that matter is not composed of atoms, or that the surface of the Earth is not divided into solid plates that have moved over geological timescales (the theory of plate tectonics)...One of the most useful properties of scientific theories is that they can be used to make predictions about natural events or phenomena that have not yet been observed.[16]

http://en.wikipedia.org/wiki/Theory#Definitions_from_scientific_organizations

Hypothesis

People refer to a trial solution to a problem as a hypothesis, often called an "educated guess"[8][9] because it provides a suggested solution based on the evidence. Some scientists reject the term "educated guess" as incorrect, however.[10] Experimenters may test and reject several hypotheses before solving the problem.
According to Schick and Vaughn,[11] researchers weighing up alternative hypotheses may take into consideration:
Testability (compare falsifiability as discussed above)
Parsimony (as in the application of "Occam's razor", discouraging the postulation of excessive numbers of entities)
Scope – the apparent application of the hypothesis to multiple cases of phenomena
Fruitfulness – the prospect that a hypothesis may explain further phenomena in the future
Conservatism – the degree of "fit" with existing recognized knowledge-systems.

http://en.wikipedia.org/wiki/Hypothesis#Scientific_hypothesis

Law

While scientific theories and laws are both based on hypotheses, a scientific theory is an explanation of the observed phenomenon, while a scientific law is a description of an observed phenomenon

Both scientific laws and theories are supported by a large body of empirical data; both help unify a particular field of scientific study; and both are widely accepted by the vast majority of scientists within a discipline.