collissions

Collisions, despite the common misspelling collissions, is the term used to describe events in which two or more bodies exert forces on each other over a short time, leading to changes in their motion and, in some cases, their internal state. The concept spans everyday experiences, scientific study, and cosmic processes.

In physics, collisions are analyzed through conservation laws. The total momentum of a closed system is conserved, with impulse transferring momentum between the involved bodies. The outcome depends on how kinetic energy changes: elastic collisions conserve kinetic energy, while inelastic collisions do not, with some energy dissipated as heat, sound, or deformation. A perfectly inelastic collision leaves the bodies stuck together and moving as a single mass after impact.

Collisions occur across scales. Macroscopically, car crashes and sports impacts illustrate momentum transfer and safety design. Microscopically, particle collisions in accelerators probe fundamental forces and constituents of matter. In astronomy and planet formation, collisions between asteroids and protoplanets contribute to growth, fragmentation, and the creation of craters, influencing the structure of planetary systems.

In computing and information systems, a different use of the term refers to hash collisions, where two inputs produce the same hash value. Such collisions require strategies for resolution, such as chaining or open addressing in data structures.

Key concepts used to study collisions include the coefficient of restitution, which quantifies how bouncy a collision is, and the center-of-mass frame, which simplifies analysis by focusing on the motion relative to the system’s collective motion.