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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.


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.


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

See collision detection.


References in classic literature ?
Altogether collisions between the classes of the old society further, in many ways, the course of development of the proletariat.
It is so easy for an Englishman to sneer at these chance collisions of human beings.
He felt that they had been the first rebels, and that the rebellion had been to a great extent successful; but what above all stirred the hatred and bitterness of his heart against them was that in the frequent collisions which there had been of late they had openly called him coward and sneak.
That light-haired gentleman followed close upon their heels, at least backing up Mr Boffin in a literal sense, if he had not had recent opportunities of doing so spiritually; while Mr Boffin, trotting on as hard as he could trot, involved Silas Wegg in frequent collisions with the public, much as a pre- occupied blind man's dog may be seen to involve his master.
No wonder, when there is this contrast between the outward and the inward, that painful collisions come of it.
I directed him, with jocose reference to the collision of interests between us, to address his letter: "Tit for Tat, Post-office, West Strand.
We were not waylaid by robbers, we fed and slept unchallenged at inns, we escaped collision with the police, and we encountered no bodily dangers of any kind; yet should I not call the journey uneventful, nor indeed, I think, would Nicolete.
The public debt of the Union would be a further cause of collision between the separate States or confederacies.
If even the angle of a respectable Triangle in the middle class is not without its dangers; if to run against a Working Man involves a gash; if collision with an officer of the military class necessitates a serious wound; if a mere touch from the vertex of a Private Soldier brings with it danger of death; -- what can it be to run against a Woman, except absolute and immediate destruction?
As the craft neared the building, and just before she struck, the Martian warriors swarmed upon her from the windows, and with their great spears eased the shock of the collision, and in a few moments they had thrown out grappling hooks and the big boat was being hauled to ground by their fellows below.
Any moment a collision might have occurred which would have been fatal to us.
Stent and Ogilvy, anticipating some possibilities of a collision, had telegraphed from Horsell to the barracks as soon as the Martians emerged, for the help of a company of soldiers to protect these strange creatures from violence.