Particle

 ( Broad-concept Articles ) 

In the physical sciences, a particle (or corpuscle in older texts) is a small physical body which can be described by several physical or chemical properties, such as volume, density, or mass. They vary greatly in size or quantity, from subatomic particles like the electron, to microscopic particles like and , to macroscopic particles like powders and other granular materials. Particles can also be used to create of even larger objects depending on their density, such as moving in a crowd or celestial bodies in motion.

The term particle 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.

However, the noun particulates is most frequently used to refer to air pollution in the Earth's atmosphere, which are a suspension of unconnected particles, rather than a connected particle aggregation.

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Conceptual properties The concept of particles is especially useful when modelling nature, as the full treatment of many phenomena can be complex and also involve difficult computation. It can be used to make simplifying assumptions concerning the processes involved. Francis Sears and Mark Zemansky, in University Physics, give the example of calculating the landing location and speed of a baseball thrown in the air. They gradually strip the baseball of most of its properties, by first idealizing it as a rigid smooth sphere, then by neglecting rotation, buoyancy and friction, ultimately reducing the problem to the ballistics of a classical point particle. The treatment of large numbers of particles is the realm of statistical physics.

Reif (1965). 9780070518001, McGraw-Hill. ISBN 9780070518001

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Size The term "particle" is usually applied differently to three classes of sizes. The term macroscopic particle, usually refers to particles much larger than and . These are usually abstraction as point particle, even though they have volumes, shapes, structures, etc. Examples of macroscopic particles would include powder, dust, sand, pieces of debris during a car accident, or even objects as big as the of a galaxy.

Another type, microscopic particles usually refers to particles of sizes ranging from to , such as carbon dioxide, , and colloid. These particles are studied in chemistry, as well as atomic physics and molecular physics.

The smallest particles are the subatomic particles, which refer to particles smaller than atoms. These would include particles such as the constituents of atoms – , , and – as well as other types of particles which can only be produced in particle accelerators or . These particles are studied in particle physics.

Because of their extremely small size, the study of microscopic and subatomic particles falls in the realm of quantum mechanics. They will exhibit phenomena demonstrated in the particle in a box model,

Reif (1965). 9780070518001, McGraw-Hill. . ISBN 9780070518001

including wave–particle duality,

R. (1985). 9780471873730, John Wiley & Sons. ISBN 9780471873730

R. (1985). 9780471873730, John Wiley & Sons. ISBN 9780471873730

and whether particles can be considered distinct or identical

Reif (1965). 9780070518001, McGraw-Hill. ISBN 9780070518001

Reif (1965). 9780070518001, McGraw-Hill. ISBN 9780070518001

is an important question in many situations.

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Composition Particles can also be classified according to composition. Composite particles refer to particles that have – that is particles which are made of other particles. For example, a carbon-14 atom is made of six protons, eight neutrons, and six electrons. By contrast, elementary particles (also called fundamental particles) refer to particles that are not made of other particles. According to our Standard Model, only a very small number of these exist, such as , , and . However it is possible that some of these preon, and merely appear to be elementary to scientists now.

I. A. (1992). 9789810210199, World Scientific. ISBN 9789810210199

While composite particles can very often be considered point particle, although having internal structure, elementary particles have so far been found to have no structure.

US National Research Council (1990). 9780309035767, US National Research Council. ISBN 9780309035767

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Stability Both elementary (such as ) and composite particles (such as uranium atomic nucleus), are known to undergo particle decay. Those that do not are called stable particles, such as the electron or a helium-4 atomic nucleus. The mean lifetime of stable particles can be either infinity 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 of radiation, such as the emission of .

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N-body simulation In computational physics, N-body simulations (also called N-particle simulations) are simulations of of particles under the influence of certain conditions, such as being subject to gravitation. These simulations are common in cosmology and computational fluid dynamics.

N refers to the particle number considered. As simulations with higher N 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 be optimized through various methods.

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Distribution of particles Colloidal particles are the components of a colloid. A colloid is a substance microscopically dispersed evenly throughout another substance. Such colloidal system can be solid, liquid, or ; as well as continuous or dispersed. The dispersed-phase particles have a diameter of between approximately 5 and 200 nanometre.

Levine (2025). 9780072318081, McGraw-Hill. . ISBN 9780072318081

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 of interface and colloid science. Suspended solids may be held in a liquid, while solid or liquid particles suspended in a gas together form an aerosol. Particles may also be suspended in the form of atmospheric particulate matter, which may constitute air pollution. Larger particles can similarly form marine debris or space debris. A conglomeration of discrete solid, macroscopic particles may be described as a granular material.

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See also

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Further reading

• Griffiths (2025). 9783527406012, Wiley-VCH. ISBN 9783527406012

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