Which principle states that energy cannot be created or destroyed?

The principle that states that energy cannot be created or destroyed is known as conservation of energy. This fundamental concept in physics indicates that the total amount of energy in a closed system remains constant over time. This means that energy can be transformed from one form to another—for example, from kinetic energy to potential energy—but the overall total will not change.

This principle is vital in understanding various phenomena in physics, such as mechanical systems, electrical circuits, and thermal processes. In practical applications, it allows scientists and engineers to analyze energy systems, ensuring conservation is maintained when designing experiments or technologies.

Other principles listed, such as the law of conservation of momentum, focus on the relationship of momentum in isolated systems, while thermal dynamics looks at heat transfer and energy changes within systems. Newton's laws primarily describe motion and forces acting on objects, rather than the conservation of energy principle directly. Thus, conservation of energy is the correct answer, capturing the essence of energy interactions within any physical system.