# collision

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## collision

Physics an event in which two or more bodies or particles come together with a resulting change of direction and, normally, energy

## Collision (physics)

Any interaction between particles, aggregates of particles, or rigid bodies in which they come near enough to exert a mutual influence, generally with exchange of energy. The term collision, as used in physics, does not necessarily imply actual contact.

In classical mechanics, collision problems are concerned with the relation of the magnitudes and directions of the velocities of colliding bodies after collision to the velocity vectors of the bodies before collision. When the only forces on the colliding bodies are those exerted by the bodies themselves, the principle of conservation of momentum states that the total momentum of the system is unchanged in the collision process. This result is particularly useful when the forces between the colliding bodies act only during the instant of collision. The velocities can then change only during the collision process, which takes place in a short time interval. Under these conditions the forces can be treated as impulsive forces, the effects of which can be expressed in terms of an experimental parameter known as the coefficient of restitution. See Conservation of momentum, Impact

The study of collisions of molecules, atoms, and nuclear particles is an important field of physics. Here the object is usually to obtain information about the forces acting between the particles. The velocities of the particles are measured before and after collision. Although quantum mechanics instead of classical mechanics should be used to describe the motion of the particles, many of the conclusions of classical collision theory are valid. See Scattering experiments (atoms and molecules), Scattering experiments (nuclei)

Collisions can be classed as elastic and inelastic. In an elastic collision, mechanical energy is conserved; that is, the total kinetic energy of the system of particles after collision equals the total kinetic energy before collision. For inelastic collisions, however, the total kinetic energy after collision is different from the initial total kinetic energy.

In classical mechanics the total mechanical energy after an inelastic collision is ordinarily less than the initial total mechanical energy, and the mechanical energy which is lost is converted into heat. However, an inelastic collision in which the total energy after collision is greater than the initial total energy sometimes can occur in classical mechanics. For example, a collision can cause an explosion which converts chemical energy into mechanical energy. In molecular, atomic, and nuclear systems, which are governed by quantum mechanics, the energy levels of the particles can be changed during collisions. Thus these inelastic collisions can involve either a gain or a loss in mechanical energy.

## collision

[kə′lizh·ən]
(physics)
An interaction resulting from the close approach of two or more bodies, particles, or systems of particles, and confined to a relatively short time interval during which the motion of at least one of the particles or systems changes abruptly.

## collision

(networking)
When two hosts transmit on a network at once causing their packets to corrupt each other.

See collision detection.

## collision

(programming)
References in periodicals archive ?
One of the colliding galaxies rotates in a direction opposite to that of its orbit.
This starburst, whose colliding galaxies have merged into a single body, lies about 120 million light-years from Earth.
The increased energy available at that facility and the use of two colliding beams of nuclei instead of one beam and a fixed target should greatly enhance the chances of creating a quark-gluon plasma.
The Eurasian and North American plates are colliding slowly, so researchers expect that it takes about a thousand years to store enough energy to trigger an earthquake along a particular patch of the subduction zone, says Abe.
Neupert had proposed that as electrons accelerate to high energies, emitting radio waves and colliding with atoms to create the hard X-rays, they also heat the ionized gas inside neighboring magnetic loops.
Up to now Soviet physicists have concentrated their electron-positron colliding beam work at Novosibirsk, where the late Gersh Budker pioneered the conception and construction of such equipment.
Thus, some anomalous events that occurred at the PETRA colliding beam apparatus of the German Electron Synchrotron Laboratory (DESY) in Hamburg back in 1984 are now being interpreted as what Harald Fritzsch of DESY calls "a peephole' into a possible new domain of physics (quoted in the September CERN COURIER).
One of these accelerators is the Intersecting Storage Rings (ISR), an apparatus that would be capable of accelerating two beams of ions and colliding them head-on.
Each colliding proton and antiproton will carry half the amount, more than 1,000 times its own rest energy.
Meanwhile the apparatus for making and controlling antiprotons and feeding them into the Tevatron was under construction with the intention of beginning colliding beam experiments sometime in 1986.

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