Those who have poured viscous liquids like syrup or honey are familiar with how they stack up in a rope-like coil, as shown in the top row of images above. What is less familiar, thanks to the high speed at which it occurs, is the Kaye effect, which happens in fluids like shampoo when drizzled. Shampoo is a shear-thinning liquid, meaning that it becomes less viscous when deformed. Like a normal Newtonian fluid, shampoo first forms a heap (bottom row, far left). But instead of coiling neatly, the heap ejects a secondary outgoing jet. This occurs when a dimple forms in the heap due to the impact of the inbound jet. The deformation causes the local viscosity to drop at the point of impact and the jet slips off the heap. The formation is unstable, causing the heap and jet to collapse in just a few hundred milliseconds, at which point the process begins again. (Image credit: L. Courbin et al.)
The Kaye Effect
