Water entry dynamics
Water entry is a classical fluid dynamics phenomenon that has been studied since the pioneering experiments of Worthington & Cole (c. 1897). With applications to entry of missiles and water-walking creatures, this topic is still revealing truly fascinating features that so far elude a proper theoretical description. A great example of this is the buckling instability.
Buckling instability
When a sphere impacts onto a quiescent water surface, an ejecta emerges and forms a crown splash. The wall of this crown can be subject to air drag and underpressure, which causes it to collapse inward. When this happens, a buckling instability occurs, where distinct ribs form. This has been compared to the wrinkling of elastic sheets, but the underlying physics are still unresolved (see our recent JFM paper and focus on fluids review here).
Hot balls splash and sink fast!
If a superheated sphere is immersed in a liquid, it can create an inverse Leidenfrost effect, where the sphere becomes wrapped in a vapor jacket, prohibiting contact with the surrounding bulk liquid. When the sphere is dropped onto a tank of liquid, the splash it creates can be quite different from a cold sphere. It also sinks considerably faster.
