Particle

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.

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, 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.

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. |access-date = 2010-02-08 |url-status = dead |archive-url = https://web.archive.org/web/20110305235040/http://science.yourdictionary.com/subatomic-particle |archive-date = 2011-03-05

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, including wave–particle duality, and whether particles can be considered distinct or identical 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. |access-date = 2010-02-08 |url-status = dead |archive-url = https://web.archive.org/web/20101115083717/http://science.yourdictionary.com/composite-particle |archive-date = 2010-11-15 |access-date = 2010-02-08 |url-status = dead |archive-url = https://web.archive.org/web/20101014204411/http://science.yourdictionary.com/elementary-particle |archive-date = 2010-10-14 While composite particles can very often be considered point-like, although having internal structure, elementary particles have so far been found to have no structure. |author-link=United States National Research Council |chapter-url=https://books.google.com/books?id=nRqq7Lov7IwC&pg=PA19

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

Main article: 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. 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.

Distribution of particles

Main article: Colloid

Colloidal particles are the components of a colloid. A colloid is a substance microscopically dispersed evenly throughout another substance. |access-date=2015-04-12 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.

References

References

1. Dubinski. (2003). "Galaxy Dynamics and Cosmology on Mckenzie". [[Canadian Institute for Theoretical Astrophysics]].
2. Graps. (20 March 2000). "N-Body / Particle Simulation Methods".