{{Short description|Sudden surface disturbance of quiet liquids}} {{Other uses|Splash (disambiguation)}} {{More footnotes|date=January 2019}}[[File:Splash (fluid mechanics).jpg|thumb|180px|A splash after half a [[brick]] hits the water; the image is about half a metre across. ]] [[Image:Water splashes 001.jpg|180px|thumb|A drop of water splashing onto a hard surface]] [[File:Water drop impact on a water-surface - (2).jpg|thumb|{{center|A drop of water splashing onto a water surface, showing the formation of a back-jet}}]] [[File:Slow Motion splash - 2022 Nov 24.webm|thumb|Slow motion video of a fruit falling into water.]]
{{More citations needed section|date=January 2026}} In [[fluid mechanics]], a '''splash''' is a sudden disturbance to the otherwise quiescent [[free surface]] of a liquid (usually [[water]]). The disturbance is typically caused by a solid object suddenly hitting the surface, although splashes can occur in which moving liquid supplies the energy. This use of the word is [[onomatopoeia|onomatopoeic]]; in the past, the term "'''plash'''" has also been used.
Splash also happens when a liquid [[droplet]] impacts on a liquid or a solid surface; in this case, a symmetric ''corona'' (resembling a [[coronet]]) is usually formed as shown in [[Harold Eugene Edgerton|Harold Edgerton]]'s famous milk splash photography, as [[milk]] is opaque. Historically, Worthington (1908) was the first one who systematically investigated the splash dynamics using photographs.
Splashes are characterized by transient [[Ballistics|ballistic]] flow, and are governed by the [[Reynolds number]] and the [[Weber number]]. In the image of a brick splashing into water, one can identify freely moving airborne water droplets, a phenomenon typical of high Reynolds number flows; the intricate non-spherical shapes of the droplets show that the Weber number is high. Also seen are entrained air bubbles in the body of the water, and an expanding ring of disturbance propagating away from the impact site.
[[Sand]] is said to splash if hit sufficiently hard (see [[dry quicksand]]) and sometimes the impact of a [[meteorite]] is referred to as splashing, if small bits of ejecta are formed.
Physicist Lei Xu and coworkers at the [[University of Chicago]] discovered that the splash due to the impact of a small drop of [[ethanol]] onto a dry solid surface could be suppressed by reducing the pressure below a specific threshold. For drops of diameter 3.4 mm falling through [[air]], this pressure was about 20 [[kilopascal]]s, or 0.2 [[atmosphere (unit)|atmosphere]].<ref>{{cite journal | last1=Xu | first1=Lei | last2=Zhang | first2=Wendy W. | last3=Nagel | first3=Sidney R. | title=Drop Splashing on a Dry Smooth Surface | journal=Physical Review Letters | publisher=American Physical Society (APS) | volume=94 | issue=18 | date=2005-05-11 | issn=0031-9007 | doi=10.1103/physrevlett.94.184505 | article-number=184505| pmid=15904376 | arxiv=physics/0501149 | bibcode=2005PhRvL..94r4505X | s2cid=19178437 }}</ref>
A plate made of a hard material on which a stream of liquid is designed to fall is called a "splash plate". It may serve to protect the ground from [[erosion]] by falling water, such as beneath an [[artificial waterfall]] or water outlet in soft ground. Splash plates are also part of [[spray nozzle]]s, such as in [[irrigation sprinkler]] systems.
==See also== *[[Drop impact]] *[[Slosh]], other free surface phenomenon
== References == {{Reflist}}
[[Category:Fluid dynamics]]