A physical law, scientific law, or a law of nature is a scientific generalization based on empirical observations of physical behavior. Empirical laws are typically conclusions based on repeated scientific experiments over many years, and which have become accepted universally within the scientific community. The production of a summary description of nature in the form of such laws is a fundamental aim of science.
Laws of nature are distinct from the law, either religious or civil, and should not be confused with the concept of natural law. Nor should 'physical law' be confused with 'law of physics' - the term 'physical law' usually covers laws in other sciences (e.g. biology) as well.
Origin of laws of nature
Some extremely important laws are simply definitions. For example, the central law of mechanics F = dp/dt (Newton's second "law" of mechanics) is often treated as a mathematical definition of force. Although the concept of force predates Newton's law, there was no mathematical definition of force before Newton. The principle of least action (or principle of stationary action), Schroedinger equation, Heisenberg's uncertainty principle, causality and a few other laws also fall into this category (of mathematical definitions).
Physical law Facts for Kids. Kiddle Encyclopedia.