# collision

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Related to collision: elastic collision, Collision theory

## 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 classic literature ?
Thus prepared to regard each other with no very cordial eye, it is not to be wondered at that the parties soon came into collision.
SABLE ISLAND--Green single barbette-tower freighter, number indistinguishable, up-ended, and fore-tank pierced after collision, passed 300-ft.
The cycles in which the stars move are those best adapted for the evolution, without collision, of the greatest possible number of bodies.
No one seeing it, even for a flash, could doubt that the room had been the theatre of some thrilling collision between two, or perhaps more, persons.
They walked about the garden paths with thoughts of their own concerns entirely uppermost, bringing their actions at every moment in jarring collision with the dim ghosts behind them, talking as though the time when Tess lived there were not one whit intenser in story than now.
For the moment her vanity was dead, stunned by collision with the realities.
Almost at the instant of impact I turned my bows upward, and then with a shattering jolt we were in collision.
With her fell a shower of her own tiny fliers, for each of them had come in violent collision with the solid shaft.
The car, which was of a circular form and fifteen feet in diameter, was made of wicker-work, strengthened with a slight covering of iron, and protected below by a system of elastic springs, to deaden the shock of collision.
The two puny things standing between them seemed already lost, but at the very moment that the beasts were upon them the man grasped his companion by the arm and together they leaped to one side, while the frenzied creatures came together like locomotives in collision.
A collision on the elevated, a panic scramble of the uninjured out upon the trestle over the street, a step on the third rail, and Harry Del Mar was engulfed in the Nothingness which men know as death and which is nothingness in so far as such engulfed ones never reappear nor walk the ways of life again.
Troy, whose practice as a solicitor had thus far never brought him into collision with thieves and mysteries.

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