Editing Mean free path (section)

===Acoustics===
In an otherwise empty cavity, the mean free path of a single particle bouncing off the walls is:

:<math>\ell = \frac{F V}{S},</math>

where ''V'' is the volume of the cavity, ''S'' is the total inside surface area of the cavity, and ''F'' is a constant related to the shape of the cavity. For most simple cavity shapes, ''F'' is approximately 4.<ref name="YoungRW">{{cite journal|last1=Young|first1=Robert W.|title=Sabine Reverberation Equation and Sound Power Calculations|journal=The Journal of the Acoustical Society of America|date=July 1959|volume=31|issue=7|page=918|doi=10.1121/1.1907816|bibcode=1959ASAJ...31..912Y}}</ref>
 
This relation is used in the derivation of the [[Reverberation|Sabine equation]] in acoustics, using a geometrical approximation of sound propagation.<ref>Davis, D. and Patronis, E. [https://books.google.com/books?id=9mAUp5IC5AMC&pg=PA173 "Sound System Engineering"] (1997) Focal Press, {{ISBN|0-240-80305-1}} p. 173.</ref>