The way gases and liquids mix and move is a surprisingly complex topic. Each year, the APS Division of Fluid Dynamics hosts its Gallery of Fluid Motion. Here, the simple addition of food dye leads to "chaotic mixing" and "pulsations" of colour.

Fluid dynamics has a number of applications, from the bizarre to the mundane. The way water is spun up by tyres - here, exiting as a thin sheet that develops holes and arcs - is of particular interest to safety regulators and tyre makers.

The way fuel is "atomised" has profound effects on the efficiency of combustion engines. In this simulation, fuel is pumped in from below into a pressurised and turbulent environment mimicking the inside of a jet engine.

You might expect three jets of liquid would merge into one. But with some fluids - in this case silicone oil - a thin film of air keeps the streams separate, making the oil jets bend and bounce off one another.

Oil does mix with water, with the help of soap. A mixture of the three added to pure water from the centre of this image creates a spreading "front" of oil droplets at the edges that, after a particular distance, mix in spectacular, turbulent vortices.

Some materials such as Lotus leaves shed water because they are "superhydrophobic". Water drops on this microscopic artificial "bed of nails" coalesce randomly, but researchers aim to design superhydrophobic materials that shed water by design.