Editing Drop (liquid) (section)

== Surface tension ==
[[Image:Bouncing droplets compact size.gif|left|120px|thumb|Drop of water bouncing on a water surface subject to vibrations]]
[[File:Water droplet surviving an attempt to be cut by a knife.ogv|thumb|Surface tension prevents water droplet from being cut by a hydrophobic knife.]]
Liquid forms drops because it exhibits [[surface tension]].<ref>{{Cite book|url=https://books.google.com/books?id=o8MdoOd6pOcC&pg=PA196|title=The American Desk Encyclopedia|last=Luck|first=Steve|date=1998|publisher=Oxford University Press, USA|isbn=978-0-19-521465-9|page=196}}</ref>

A simple way to form a drop is to allow liquid to flow slowly from the lower end of a vertical tube of small diameter. The surface tension of the liquid causes the liquid to hang from the tube, forming a pendant. When the drop exceeds a certain size it is no longer stable and detaches itself. The falling liquid is also a drop held together by surface tension.

=== Viscosity and pitch drop experiments===
{{main|Viscosity|Pitch drop experiment}}
Some substances that appear to be solid, can be shown to instead be extremely [[viscosity|viscous]] liquids, because they form drops and display droplet behavior. In the famous [[pitch drop experiment]]s, [[pitch (resin)|pitch]] – a substance somewhat like solid [[bitumen]] – is shown to be a liquid in this way. Pitch in a funnel slowly forms droplets, each droplet taking about 10 years to form and break off.