Why is energy conserved during elastic and inelastic collisions?

In the study of physical science, the conservation of energy is a fundamental principle stating that energy is neither created nor destroyed, but merely changes form. While the total energy of a closed system remains constant, the way it is distributed during a collision depends on the nature of the interaction.12

In a perfectly elastic collision, the total kinetic energy of the particles before the impact is equal to the total kinetic energy after the impact. No kinetic energy is transformed into other forms of energy.13

In an inelastic collision, some of the external kinetic energy of the colliding bodies is transformed into other forms, such as heat or internal energy, which relates to the random motions of the atoms or molecules within the objects. Although the kinetic energy of the system decreases, the total energy—the sum of external kinetic, potential, and internal thermal energy—remains conserved. This is consistent with the first law of thermodynamics, which accounts for all energy transfers, including heat.451