Final answer:
The principle of conservation of energy in physics asserts that energy cannot be created or destroyed but can change forms within an isolated system, a concept supported by both classical and relativistic physics.
Step-by-step explanation:
The principle of conservation of energy is a fundamental concept in physics stating that energy cannot be created or destroyed within an isolated system. The total amount of energy remains constant, though it can be transformed from one form to another. Classical physics maintains that this conservation applies to all systems, and this has been borne out through countless experiments.
In the context of relativity, energy conservation holds true as well when the definition of energy includes the conversion of mass into energy, as per Einstein's famous equation E = mc². Relativistic energy is conserved in all inertial frames, as is relativistic momentum, underscoring the interconnectedness and conservation of fundamental physical quantities.
Historical experiments, such as those conducted by Émilie du Châtelet, helped solidify the law of energy conservation, paving the way for the comprehensive understanding we have today, which spans multiple forms of energy, including kinetic and potential energy, as well as mass-energy equivalence in relativity.