Which principle states that energy is not created or destroyed, but only changes forms?

The principle that states energy is not created or destroyed, but only changes forms is the Law of Conservation of Energy. This fundamental concept in physics asserts that the total amount of energy in a closed system remains constant over time. In practical terms, this means that energy can be transformed from one type to another—such as potential energy converting to kinetic energy or chemical energy converting to thermal energy—yet the total energy remains unchanged throughout these transformations.

This principle is critical in numerous fields, ranging from engineering and environmental science to understanding physical systems in mechanics and thermodynamics. For example, when a ball is thrown into the air, its kinetic energy decreases as it rises (slowing down) and converts into potential energy, which is then converted back into kinetic energy as it falls.

Other principles mentioned do not directly relate to energy transformation in this way; therefore, they do not encompass the fundamental idea of energy conservation as clearly or directly as the Law of Conservation of Energy does. Understanding this principle provides a foundational basis for analyzing energy interactions in various physical and chemical processes.