Law (in science)
High school
A scientific law is a statement, often an equation, that describes a pattern that holds in every tested case, without explaining why.
Examples
Examples
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Newton’s law of universal gravitation, $F = G m_1 m_2 / r^2$
High school
Newton’s law of gravitation is a law because it is an equation that describes how strongly masses attract.
Non-examples
Things that may be mistaken for examples.
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Before an experiment: “Bean plants grow taller with more hours of light each day”
Elementary
The hypothesis “Bean plants grow taller with more hours of light each day” is not a law, because it has not been observed to hold in every tested case.
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The theory of evolution by natural selection
High school
Evolution by natural selection is not a law because it explains why species change rather than describing one pattern.
Properties
- A law describes what happens, and a theory explains why. A theory does not become a law by gaining more evidence.
Distinctions involving this term
- Conjecture vs. hypothesis vs. law vs. theory: Mathematics and science both have words for statements that are proposed, tested, or established, and the words are often confused. A conjecture is a statement believed true but not yet proved, and it belongs to mathematics, where statements are settled by proof. In science, where statements are tested by evidence, a hypothesis is a testable proposal, and a theory is a well-supported explanation of many observations. A law describes a pattern that holds in every tested case, often as an equation such as $F = G m_1 m_2 / r^2$, without explaining why the pattern holds; explaining it is the job of a theory. In everyday speech, “theory” means a guess, but in science a theory is an a principle or body of principles that explains observed data and phenomenon.