What does the law of conservation of energy imply about energy changes within an isolated system?

The law of conservation of energy states that energy cannot be created or destroyed; it can only change forms. This principle applies to isolated systems where the total energy remains constant, regardless of the processes that occur within the system.

When energy changes occur—such as mechanical work being transformed into thermal energy or chemical energy being converted to kinetic energy—the total amount of energy before and after the change is balanced. For instance, if a ball is thrown into the air, the kinetic energy is converted to potential energy at its peak and then back to kinetic energy as it falls. Throughout this process, the sum total of energy remains constant, illustrating the law of conservation of energy in action.

This clear and fundamental principle is what makes the first choice the correct answer. It emphasizes that while energy can shift between different forms or locations within a system, the overall quantity of energy must remain unchanged.