In a closed system, what remains constant during an event?

In a closed system, the principle of conservation of energy states that the total energy remains constant during an event. This means that the energy can neither be created nor destroyed but can only change forms. For instance, potential energy can convert into kinetic energy, thermal energy, and so forth, yet the total amount of energy remains unchanged.

This principle is fundamental in mechanics and helps to understand how energy transformation occurs in various processes, whether in mechanical systems like pendulums or in thermodynamic systems. If energy seems to be lost, it has often been converted to a less useful form, such as heat, but its total quantity remains constant.

Other aspects such as mass, temperature, and force do not have the same invariant nature under all conditions. For example, mass is generally conserved in closed systems, but in certain nuclear reactions, mass-energy equivalence indicates that mass can be converted to energy. Temperature is a variable and can change due to energy transformations. Force, on the other hand, pertains to interactions affecting the motion of objects but does not have a conservation law like energy. Thus, in the context of a closed system, total energy is the quantity that always stays constant.