Sound particle

Not to be confused with the phonon, a quantum quasiparticle used to describe very high frequency vibrations.

In continuum mechanics, specifically in acoustics, a sound particle refers to a material element in a medium through which an acoustic wave is transmitted.

Here, the term material element is only applicable in the continuum model of matter, where a material body is assumed to consist of uncountably infinitely many points (called material points), which take up all the space within the region of the body. In other words, a material body is assumed to be (the closure of) a regular open, connected bounded subset of either $\mathbb {R}$, $\mathbb {R} ^{2}$ or $\mathbb {R} ^{3}$, depending on whether the body is a one-dimensional elastic rod, a two-dimensional elastic lamina, or a three-dimensional elastic body, respectively. A material medium is defined in the same way, except that it need not be a bounded subset.

The continuum model of matter ignores that matter is made of finitely small, discrete particles (atoms or molecules); the material points in a continuum body are modelled as points in Euclidean space, and are not to be visualized as finitely small, discrete particles.