Which law states that energy cannot be created or destroyed, only transformed from one form to another?

The principle that energy cannot be created or destroyed but can only be transformed from one form to another is known as the First Law of Thermodynamics. This law is foundational to the field of thermodynamics and underlines the notion that in any energy transfer or transformation, the total amount of energy remains constant.

For example, when you consume food, your body transforms the chemical energy stored in the food into kinetic energy for movement and thermal energy to maintain body temperature. Throughout these processes, energy is not lost but rather changes from one form to another, demonstrating the core tenet of this law.

The other options, while related to energy, describe different aspects. The Second Law of Thermodynamics addresses the concept of entropy and the direction of energy transformations (noting that they tend to become more disordered). The Law of Conservation of Energy is often used interchangeably with the First Law of Thermodynamics but is not a formal law in the same scientific context, whereas the Law of Energy Transformation is a less recognized phrase that does not specifically capture the principle stated in the question. Therefore, the First Law of Thermodynamics directly encapsulates the concept that energy can only be transformed and not created or destroyed.