A scientific law is a statement or mathematical equation that describes or predicts a natural phenomenon. It does not explain why or how a phenomenon occurs. Another name for a scientific law is a law of nature or law of science. All scientific laws are based on empirical evidence and the scientific method. In science, an assertion can be disproven, but never proven, so it’s possible for a scientific law to be revised or disproven by future experiments. In contrast, a mathematical theorem or identity is proven to be true.
Examples of Scientific Laws
There are laws in all scientific disciplines, although primarily they are physical laws. Here are some examples:
- Beer’s law
- Dalton’s law of partial pressures
- Ideal gas law
- Kepler’s laws of planetary motion
- Law of conservation of mass
- Law of conservation of energy
- Law of conservation of momentum
- Law of reflection
- Laws of thermodynamics
- Newton’s law of universal gravitation
- Newton’s laws of motion
Difference Between a Scientific Law and Scientific Theory
Both scientific laws and scientific theories are based in the scientific method and are falsifiable. However, the two terms have very different meanings. A law describes what happens, but does not explain it. A theory explains how or why something works.
For example, Newton’s law of universal gravitation describes what happens when two masses are a given distance apart. The law can be written as a mathematical equation [F = G(m1m2/r2)] and used to make predictions and calculations. However, the law does not explain how gravity works or why two masses are attracted to one another. Scientists didn’t really have an explanation for gravity until Einstein’s theory of general relativity, which continues to be revised as we understand more about the nature of spacetime.
As another example, Hubble’s law of Cosmic Expansion (velocity = Hubble constant x distance) describes the movement of galaxies away from each other. It does explain why this occurs. The Big Bang Theory is one of the theories that explains why galaxies move apart, but the theory does not offer a formula for calculating this motion.
Can a Hypothesis or Theory Become a Law?
A hypothesis, theory, and law are all parts of scientific inquiry, but one never becomes another. They are different things. A hypothesis never becomes a theory, no matter how many experiments support it, because a hypothesis is simply a prediction about how one variable responds when another is changed. A theory takes into account the results of many experiments, testing different hypotheses. A theory explains how something works. Like a theory, a law draws on the results of repeated observations and experiments. But, a law states in words or mathematical equations what happens. Laws don’t explain why.
- Barrow, John (1991). Theories of Everything: The Quest for Ultimate Explanations. ISBN 0-449-90738-4.
- Feynman, Richard (1994). The Character of Physical Law (Modern Library ed.). New York: Modern Library. ISBN 978-0-679-60127-2.
- Gould, Stephen Jay (1981). “Evolution as Fact and Theory“. Discover. 2 (5): 34–37.
- McComas, William F. (2013). The Language of Science Education: An Expanded Glossary of Key Terms and Concepts in Science Teaching and Learning. Springer Science & Business Media. ISBN 978-94-6209-497-0.