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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 periodicals archive ?
Normally the OIII emission comes from collisionally excited lines of oxygen and the reasons for no OIII emission in this case could be either a low temperature central star that is not emitting enough high energy photons to excite the nebula, or a high density nebula where the energy levels that produce the OIII lines are getting collisionally de-excited before they have a chance to emit the photons, a process called damping.
However, the levels with higher n-values stay in detailed balance relative to each other at these atmospheric depths, and they also collisionally couple tightly to the continuum" [64].
2) (a) The general instrument settings used for LC/MS/MS detection and quantification of all 4 analytes in MRM mode were as follows: resolution, Q1 and Q3; unit dwell time, 180 ms; ion spray voltage, 5500 V; source temperature, 350[degrees]C; curtain gas, 25 psi; gas 1, 25 psi; gas 2, 40 psi; collisionally activated dissociation gas, 5.