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Models, Theories, and Laws

The Role of Experimentation: Models, Theories, and Laws


Isaac Newton (1642–1727) was very reluctant to publish his revolutionary work and had to be convinced to do so. In his later years, he stepped down from his academic post and became exchequer of the Royal Mint. He took this post seriously, inventing reeding (or creating ridges) on the edge of coins. This was to prevent unscrupulous people from trimming the silver off of them before using them as currency. Image Attribution: Arthur Shuster and Arthur E. Shipley: Britain’s Heritage of Science. London, 1917.

The laws of nature are concise descriptions of the universe around us. They are human statements of the underlying laws or rules that all natural processes follow. Such laws are intrinsic to the universe; humans did not create them and so cannot change them. We can only discover and understand them. Their discovery is a very human endeavor, with all the elements of mystery, imagination, struggle, triumph, and disappointment inherent in any creative effort. (See pictures above and below.) The cornerstone of discovering natural laws is observation. Science must describe the universe as it is, not as we may imagine it to be.

Marie Curie

Marie Curie (1867–1934) sacrificed monetary assets to help finance her early research and damaged her physical well-being with radiation exposure. She is the only person to win Nobel prizes in both physics and chemistry. One of her daughters also won a Nobel Prize. Image Attribution: Wikimedia Commons

We all are curious to some extent. We look around, make generalizations, and try to understand what we see. For example, we look up and wonder whether one type of cloud signals an oncoming storm. As we become serious about exploring nature, we become more organized and formal in collecting and analyzing data. We attempt greater precision and perform controlled experiments (if we can). Then, we write down ideas about how we may organize and unify the data. We then formulate models, theories, and laws based on the data we have collected and analyzed. We do this to generalize and communicate the results of these experiments.


A model is a representation of something that is often too difficult (or impossible) to display directly. While we justify a model with experimental proof, it is only accurate under limited situations. An example is the planetary model of the atom in which we picture electrons as orbiting the nucleus, analogous to the way planets orbit the Sun. (See image below.)


What is a model? This planetary model of the atom shows electrons orbiting the nucleus. It is a drawing that we use to form a mental image of the atom that we cannot see directly with our eyes because it is too small. Image Attribution: OpenStax Physics

We cannot observe electron orbits directly. However, the mental image helps explain the observations we can make, such as the emission of light from hot gases (atomic spectra). Physicists use models for a variety of purposes. For example, models can help physicists analyze a scenario and perform a calculation, or we can use them to represent a situation in the form of a computer simulation.


A theory is an explanation for patterns in nature that is supported by scientific evidence and verified multiple times by various groups of researchers. Some theories include models to help visualize phenomena, whereas others do not. Newton’s theory of gravity, for example, does not require a model or mental image, because we can observe the objects directly with our own senses. The kinetic theory of gases, on the other hand, is a model in which we view a gas as consisting of atoms and molecules. Atoms and molecules are too small for us to observe directly with our senses. Thus, we picture them mentally to understand what our instruments tell us about the behavior of gases.


A law uses concise language to describe a generalized pattern in nature that is supported by scientific evidence and repeated experiments. Often, we can express a law in the form of a single mathematical equation. Laws and theories are similar in that they are both scientific statements that result from a tested hypothesis and are supported by scientific evidence. However, the designation law is reserved for a concise and very general statement that describes phenomena in nature, such as the law that energy is conserved during any process, or Newton’s second law of motion, which relates force, mass, and acceleration by the simple equation \(F = ma.\) 

A theory, in contrast, is a less concise statement of observed phenomena. For example, we cannot express the Theory of Evolution and the Theory of Relativity concisely enough for them to become laws. The biggest difference between a law and a theory is that a theory is much more complex and dynamic. A law describes a single action, whereas a theory explains an entire group of related phenomena. And, whereas a law is a postulate that forms the foundation of the scientific method, a theory is the end result of that process.

We refer to less broadly applicable statements as principles (such as Pascal’s principle, which applies only in fluids). However, the distinction between laws and principles often is not carefully made.


Models, theories, and laws help scientists analyze already collected data. However, the development of a model, theory, or law often points scientists toward even new discoveries.

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