Particle

Last updated November 18, 2024

In the physical sciences, a particle (or corpuscule in older texts) is a small localized object which can be described by several physical or chemical properties, such as volume, density, or mass.^[1]^[2] They vary greatly in size or quantity, from subatomic particles like the electron, to microscopic particles like atoms and molecules, to macroscopic particles like powders and other granular materials. Particles can also be used to create scientific models of even larger objects depending on their density, such as humans 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.^[3] However, the noun particulate is most frequently used to refer to pollutants in the Earth's atmosphere, which are a suspension of unconnected particles, rather than a connected particle aggregation.

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.^[4] 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.^[5] The treatment of large numbers of particles is the realm of statistical physics.^[6]

Size

The term "particle" is usually applied differently to three classes of sizes. The term macroscopic particle , usually refers to particles much larger than atoms and molecules. These are usually abstracted as point-like particles, even though they have volumes, shapes, structures, and etc. Examples of macroscopic particles would include powder, dust, sand, pieces of debris during a car accident, or even objects as big as the stars of a galaxy.^[7]^[8]

Another type, microscopic particles usually refers to particles of sizes ranging from atoms to molecules, such as carbon dioxide, nanoparticles, and colloidal particles. These particles are studied in chemistry, as well as atomic and molecular physics. The smallest particles are the subatomic particles , which refer to particles smaller than atoms.^[9] These would include particles such as the constituents of atoms – protons, neutrons, and electrons – as well as other types of particles which can only be produced in particle accelerators or cosmic rays. 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,^[10]^[11] including wave–particle duality,^[12]^[13] and whether particles can be considered distinct or identical ^[14]^[15] is an important question in many situations.

Composition

Particles can also be classified according to composition. Composite particles refer to particles that have composition – that is particles which are made of other particles.^[16] 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.^[17] According to our current understanding of the world, only a very small number of these exist, such as leptons, quarks, and gluons. However it is possible that some of these might be composite particles after all, and merely appear to be elementary for the moment.^[18] While composite particles can very often be considered point-like, elementary particles are truly punctual.^[19]

Stability

Both elementary (such as muons) and composite particles (such as uranium nuclei), are known to undergo particle decay. Those that do not are called stable particles, such as the electron or a helium-4 nucleus. The lifetime of stable particles can be either infinite 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 photons.

N-body simulation

In computational physics, N-body simulations (also called N-particle simulations) are simulations of dynamical systems of particles under the influence of certain conditions, such as being subject to gravity.^[20] These simulations are common in cosmology and computational fluid dynamics.

N refers to the number of particles 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.^[20]

Distribution of particles

Examples of a stable and of an unstable colloidal dispersion. ColloidalStability.png — 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 be solid, liquid, or gaseous; as well as continuous or dispersed. The dispersed-phase particles have a diameter of between approximately 5 and 200 nanometers.^[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 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.

Related Research Articles

In particle physics, an elementary particle or fundamental particle is a subatomic particle that is not composed of other particles. The Standard Model presently recognizes seventeen distinct particles—twelve fermions and five bosons. As a consequence of flavor and color combinations and antimatter, the fermions and bosons are known to have 48 and 13 variations, respectively. Among the 61 elementary particles embraced by the Standard Model number: electrons and other leptons, quarks, and the fundamental bosons. Subatomic particles such as protons or neutrons, which contain two or more elementary particles, are known as composite particles.

<span class="mw-page-title-main">Fermion</span> Type of subatomic particle

In particle physics, a fermion is a subatomic particle that follows Fermi–Dirac statistics. Fermions have a half-odd-integer spin and obey the Pauli exclusion principle. These particles include all quarks and leptons and all composite particles made of an odd number of these, such as all baryons and many atoms and nuclei. Fermions differ from bosons, which obey Bose–Einstein statistics.

A molecule is a group of two or more atoms that are held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemistry, and biochemistry, the distinction from ions is dropped and molecule is often used when referring to polyatomic ions.

Particle physics or high-energy physics is the study of fundamental particles and forces that constitute matter and radiation. The field also studies combinations of elementary particles up to the scale of protons and neutrons, while the study of combination of protons and neutrons is called nuclear physics.

Physical chemistry is the study of macroscopic and microscopic phenomena in chemical systems in terms of the principles, practices, and concepts of physics such as motion, energy, force, time, thermodynamics, quantum chemistry, statistical mechanics, analytical dynamics and chemical equilibria.

Quantum mechanics is a fundamental theory that describes the behavior of nature at and below the scale of atoms. It is the foundation of all quantum physics, which includes quantum chemistry, quantum field theory, quantum technology, and quantum information science.

Atomic, molecular, and optical physics (AMO) is the study of matter–matter and light–matter interactions, at the scale of one or a few atoms and energy scales around several electron volts. The three areas are closely interrelated. AMO theory includes classical, semi-classical and quantum treatments. Typically, the theory and applications of emission, absorption, scattering of electromagnetic radiation (light) from excited atoms and molecules, analysis of spectroscopy, generation of lasers and masers, and the optical properties of matter in general, fall into these categories.

In physics, a subatomic particle is a particle smaller than an atom. According to the Standard Model of particle physics, a subatomic particle can be either a composite particle, which is composed of other particles, or an elementary particle, which is not composed of other particles. Particle physics and nuclear physics study these particles and how they interact. Most force-carrying particles like photons or gluons are called bosons and, although they have quanta of energy, do not have rest mass or discrete diameters and are unlike the former particles that have rest mass and cannot overlap or combine which are called fermions. The W and Z bosons, however, are an exception to this rule and have relatively large rest masses at approximately 80 GeV and 90 GeV respectively.

The macroscopic scale is the length scale on which objects or phenomena are large enough to be visible with the naked eye, without magnifying optical instruments. It is the opposite of microscopic.

In quantum physics and chemistry, quantum numbers are quantities that characterize the possible states of the system. To fully specify the state of the electron in a hydrogen atom, four quantum numbers are needed. The traditional set of quantum numbers includes the principal, azimuthal, magnetic, and spin quantum numbers. To describe other systems, different quantum numbers are required. For subatomic particles, one needs to introduce new quantum numbers, such as the flavour of quarks, which have no classical correspondence.

<span class="mw-page-title-main">Azimuthal quantum number</span> Quantum number denoting orbital angular momentum

In quantum mechanics, the azimuthal quantum number $ℓ$ is a quantum number for an atomic orbital that determines its orbital angular momentum and describes aspects of the angular shape of the orbital. The azimuthal quantum number is the second of a set of quantum numbers that describe the unique quantum state of an electron.

In condensed matter physics, a quasiparticle is a concept used to describe a collective behavior of a group of particles that can be treated as if they were a single particle. Formally, quasiparticles and collective excitations are closely related phenomena that arise when a microscopically complicated system such as a solid behaves as if it contained different weakly interacting particles in vacuum.

In physics, semiclassical refers to a theory in which one part of a system is described quantum mechanically, whereas the other is treated classically. For example, external fields will be constant, or when changing will be classically described. In general, it incorporates a development in powers of the Planck constant, resulting in the classical physics of power 0, and the first nontrivial approximation to the power of (−1). In this case, there is a clear link between the quantum-mechanical system and the associated semi-classical and classical approximations, as it is similar in appearance to the transition from physical optics to geometric optics.

In quantum mechanics, angular momentum coupling is the procedure of constructing eigenstates of total angular momentum out of eigenstates of separate angular momenta. For instance, the orbit and spin of a single particle can interact through spin–orbit interaction, in which case the complete physical picture must include spin–orbit coupling. Or two charged particles, each with a well-defined angular momentum, may interact by Coulomb forces, in which case coupling of the two one-particle angular momenta to a total angular momentum is a useful step in the solution of the two-particle Schrödinger equation. In both cases the separate angular momenta are no longer constants of motion, but the sum of the two angular momenta usually still is. Angular momentum coupling in atoms is of importance in atomic spectroscopy. Angular momentum coupling of electron spins is of importance in quantum chemistry. Also in the nuclear shell model angular momentum coupling is ubiquitous.

<span class="mw-page-title-main">Spin-1/2</span> Type of matter

In quantum mechanics, spin is an intrinsic property of all elementary particles. All known fermions, the particles that constitute ordinary matter, have a spin of ⁠1/2⁠. The spin number describes how many symmetrical facets a particle has in one full rotation; a spin of ⁠1/2⁠ means that the particle must be rotated by two full turns before it has the same configuration as when it started.

In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which are made up of interacting subatomic particles, and in everyday as well as scientific usage, matter generally includes atoms and anything made up of them, and any particles that act as if they have both rest mass and volume. However it does not include massless particles such as photons, or other energy phenomena or waves such as light or heat. Matter exists in various states. These include classical everyday phases such as solid, liquid, and gas – for example water exists as ice, liquid water, and gaseous steam – but other states are possible, including plasma, Bose–Einstein condensates, fermionic condensates, and quark–gluon plasma.

<span class="mw-page-title-main">Boson</span> Class of subatomic particle

In particle physics, a boson ( ) is a subatomic particle whose spin quantum number has an integer value. Bosons form one of the two fundamental classes of subatomic particle, the other being fermions, which have odd half-integer spin. Every observed subatomic particle is either a boson or a fermion. Paul Dirac coined the name boson to commemorate the contribution of Satyendra Nath Bose, an Indian physicist.

This glossary of physics is a list of definitions of terms and concepts relevant to physics, its sub-disciplines, and related fields, including mechanics, materials science, nuclear physics, particle physics, and thermodynamics. For more inclusive glossaries concerning related fields of science and technology, see Glossary of chemistry terms, Glossary of astronomy, Glossary of areas of mathematics, and Glossary of engineering.

References

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↑ Lambe, T. W.; Whitman, R. V. (1969). Soil Mechanics. John Wiley & Sons. p. 18. ISBN 978-0-471-51192-2. The word 'particulate' means 'of or pertaining to a system of particles'.
↑ Sears, F. W.; Zemansky, M. W. (1964). "Equilibrium of a Particle". University Physics (3rd ed.). Addison-Wesley. pp. 26–27. LCCN 63015265.
↑ F. W. Sears; M. W. Zemansky (1964). "Equilibrium of a Particle". University Physics (3rd ed.). Addison-Wesley. p. 27. LCCN 63015265. 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.
↑ Reif, F. (1965). "Statistical Description of Systems of Particles". Fundamentals of Statistical and Thermal Physics. McGraw-Hill. pp. 47ff. ISBN 978-0-07-051800-1.
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↑ Eisberg, R.; Resnick, R. (1985). "Photons—Particlelike Properties of Radiation". Quantum Physics of Atoms, Molecules, Solids, Nuclei, and Particles (2nd ed.). John Wiley & Sons. pp. 26–54. ISBN 978-0-471-87373-0.
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↑ Reif, F. (1965). "Quantum Statistics of Ideal Gases – Physical Implications of the Quantum-Mechanical Enumeration of States". Fundamentals of Statistical and Thermal Dynamics. McGraw-Hill. pp. 353–360. ISBN 978-0-07-051800-1.
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↑ "Elementary particle". YourDictionary.com. Archived from the original on 2010-10-14. Retrieved 2010-02-08.
↑ D'Souza, I. A.; Kalman, C. S. (1992). Preons: Models of Leptons, Quarks and Gauge Bosons as Composite Objects. World Scientific. ISBN 978-981-02-1019-9.
↑ US National Research Council (1990). "What is an elementary particle?". Elementary-Particle Physics. US National Research Council. p. 19. ISBN 0-309-03576-7.
1 2 Graps, A. (20 March 2000). "N-Body / Particle Simulation Methods". Archived from the original on 5 April 2001. Retrieved 2019-04-18.
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↑ Levine, I. N. (2001). Physical Chemistry (5th ed.). McGraw-Hill. p. 955. ISBN 978-0-07-231808-1.