Energy is conserved in a closed system, meaning it cannot be created or destroyed.

In such a system, energy can be transformed from one form to another, but the total amount of energy remains unchanged. This principle is known as the law of conservation of energy. According to this law, energy can neither be created nor destroyed; it can only be converted from one form into another.

For instance, consider a ball dropped from a certain height. As the ball descends, its potential energy is transformed into kinetic energy. Upon striking the ground, the kinetic energy is transferred to the ground, producing sound and heat energy. Nevertheless, the total energy of the system, comprising the ball and the Earth, remains constant.

Another illustration of energy conservation in a closed system is a pendulum swinging back and forth. During its motion, the pendulum continuously converts potential energy into kinetic energy and vice versa. Although some energy may be lost to friction as heat, the overall amount of energy within the system remains unchanged.

In summary, energy is conserved in a closed system because it cannot be created or destroyed. It can only be transformed from one form to another, ensuring that the total energy within the system remains constant.