In the absence of gravity, surface tension

In the absence of gravity, surface tension dominates the physics of fluids. Here, in an image taken on the International Space Station, it causes water to extend from a metal loop as if it were stirred by an invisible spoon.

This stirring effect was created by using a flashlight to unevenly heat the water. The resulting temperature difference induced an imbalance in the surface tension, causing the fluid to rotate.

Such surface-tension-triggered movement, called Marangoni convection, is less obvious on Earth, but can be seen in environments such as cooling puddles of molten steel.