About Physical Laws: Over the years, one thing scientists have discovered is that nature is generally more complex than we give it credit for. The following laws of physics are considered fundamental, but many of them refer to idealized, closed systems, which are hard to obtain in the real world. Also, some are altered slightly in different circumstances. Newton's laws of motion, for example, are modified by the findings of the theory of relativity, but they are still basically valid.

Newton's Three Laws of Motion: Sir Isaac Newton developed the Three Laws of Motion, which define the fundamental relationship between the net acceleration of an object and the net forces acting upon it.

"Law" of Gravity: Newton developed his "Law of Gravity" to explain the attractive force between a pair of masses. In recent years, it has become clear that this is not the whole story, as Einstein's theory of general relativity has provided a more comprehensive explanation for the phenomenon of gravity.

Conservation of Mass-Energy: The total energy in a closed or isolated system is constant, no matter what happens. Another law stated that the mass in an isolated system is constant. When Einstein discovered the relationship E=mc2, in other words that mass was a manifestation of energy, the law was said to refer to the conservation of mass-energy, which says the total of both is retained, although some may change forms. The ultimate example of this is a nuclear explosion, where mass transforms into energy.

Conservation of Momentum: The total momentum in a closed or isolated system remains constant. An alternative of this is the law of angular momentum.

Laws of Thermodynamics: The laws of thermodynamics are actually specific manifestations of the law of conservation of mass-energy as it relates to thermodynamic processes. The first law of thermodynamics demonstrates the relationship between internal energy, added heat, and work within a system. The second law of thermodynamics relates to the natural flow of heat within a closed system.

Electrostatic Laws: Coulomb's law and Gauss's law are formulations of the relationship between electrically charged particles to create electrostatic force and electrostatic fields. The formulas, it turns out, parallel the laws of universal gravitation in structure. There also exist similar laws relating to magnetism and electromagnetism as a whole.

Invariance of the Speed of Light: Einstein's major insight, which led him to the Theory of Relativity, was the realization that the speed of light in a vacuum is constant and is not measured differently for observers in different inertial frames of reference, unlike all other forms of motion.

Modern Physics & Physical Laws: In the realm of relativity and quantum mechanics, scientists have found that these laws still apply, although their interpretation requires some refinement to be applied, resulting in fields such as quantum electronics and quantum gravity. Care should be taken in applying them in these situations.

Taken from Andrew Zimmerman Jones, Your Guide to Physics.