Learn about the complexity of fluid flow and fluid knots in this video from NOVA Digital. Fluids include liquids and gases, such as water or air. Fluid flow is dependent on several factors and is hard to predict. Scientists are researching one aspect of fluids (a measure called knottedness) to better understand fluid flow. Three physicists recently advanced the field of fluid dynamics when they successfully created a knot of air using a 3D printer and a water tank. Questions remain about whether fluids conserve knottedness but engineers may someday use knottedness to develop more aerodynamic and hydrodynamic vehicles.