Particles

A particle is a minute fragment or quantity of matter. In the physical sciences, a particle is a small object to which can be ascribed several physical or chemical properties such as volume or mass. They vary greatly in size, 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, such as humans moving in a crowd or celestial bodies in motion.

The term is rather general in meaning, and is refined as needed by various scientific fields. Something that is composed of particles may be referred to as being particulate. However, the term 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.

The concept of particles is particularly useful when modelling nature, as the full treatment of many phenomena can be complex. 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.

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