The termparticle is rather general in meaning, and is refined as needed by various scientific fields. Anything that is composed of particles may be referred to as being particulate.[3] However, the nounparticulate is most frequently used to refer topollutants in theEarth's atmosphere, which are asuspension of unconnected particles, rather than a connectedparticle aggregation.
The concept of particles is especially useful whenmodellingnature, as the full treatment of many phenomena can be complex and also involve difficult computation.[4] It can be used to make simplifying assumptions concerning the processes involved.Francis Sears andMark Zemansky, inUniversity Physics, give the example of calculating the landing location and speed of abaseball thrown in the air. They gradually strip the baseball of most of its properties, by firstidealizing it as a rigid smoothsphere, then by neglectingrotation,buoyancy andfriction, ultimately reducing the problem to theballistics of aclassicalpoint particle.[5] The treatment of large numbers of particles is the realm ofstatistical physics.[6]
Particles can also be classified according to composition.Composite particles refer to particles that havecomposition – that is particles which are made of other particles.[16] For example, acarbon-14 atom is made of six protons, eight neutrons, and six electrons. By contrast,elementary particles (also calledfundamental particles) refer to particles that are not made of other particles.[17] According to ourcurrent understanding of the world, only a very small number of these exist, such asleptons,quarks, andgluons. However it is possible that some of thesemight be composite particles after all, and merely appear to be elementary for the moment.[18] While composite particles can very often be consideredpoint-like, elementary particles are trulypunctual.[19]
Both elementary (such asmuons) and composite particles (such asuraniumnuclei), are known to undergoparticle decay. Those that do not are called stable particles, such as theelectron or ahelium-4nucleus. Thelifetime of stable particles can be eitherinfinite or large enough to hinder attempts to observe such decays. In the latter case, those particles are called "observationally stable". In general, a particle decays from a high-energy state to a lower-energy state by emitting some form ofradiation, such as the emission ofphotons.
N refers to thenumber of particles considered. As simulations with higherN are more computationally intensive, systems with large numbers of actual particles will often be approximated to a smaller number of particles, and simulation algorithms need to beoptimized through various methods.[20]
Examples of a stable and of an unstable colloidal dispersion.
Colloidal particles are the components of a colloid. A colloid is a substance microscopically dispersed evenly throughout another substance.[21] Such colloidal system can besolid,liquid, orgaseous; as well as continuous or dispersed. The dispersed-phase particles have a diameter of between approximately 5 and 200nanometers.[22] Soluble particles smaller than this will form a solution as opposed to a colloid. Colloidal systems (also called colloidal solutions or colloidal suspensions) are the subject ofinterface and colloid science.Suspended solids may be held in a liquid, while solid or liquid particles suspended in a gas together form anaerosol. Particles may also be suspended in the form ofatmospheric particulate matter, which may constituteair pollution. Larger particles can similarly formmarine debris orspace debris. A conglomeration of discrete solid, macroscopic particles may be described as agranular material.
^Sears, F. W.; Zemansky, M. W. (1964). "Equilibrium of a Particle".University Physics (3rd ed.).Addison-Wesley. pp. 26–27.LCCN63015265.
^F. W. Sears; M. W. Zemansky (1964). "Equilibrium of a Particle".University Physics (3rd ed.).Addison-Wesley. p. 27.LCCN63015265.A body whose rotation is ignored as irrelevant is called a particle. A particle may be so small that it is an approximation to a point, or it may be of any size, provided that the action lines of all the forces acting on it intersect in one point.
.jpg)
