A drop of a thick cornstarch-water mixture falls onto a table. Normally, such a mixture solidifies instantly upon a sharp impact: you can even run across a pool filled with it. But in this experiment, things went differently. The high-speed camera captured that in the first instant after contact, the drop spreads out like an ordinary liquid. Only later, when the impact speed drops, does it suddenly seize up and behave like a solid.
This order (first liquid, then solid) came as a surprise. Usually, for such mixtures, it's the opposite: the harder the impact, the faster they solidify. Here, at the highest speeds, the mixture momentarily 'forgets' its unusual nature and flows like water with starch. Only when the motion slows down does it remember that it can solidify, and the drop clumps together.
This result helps us better understand the behavior of complex fluids that change their properties depending on how quickly they are compressed. Such mixtures are used in body armor, brake fluids, and even cooking. Now scientists know that under very sharp loads, these materials can behave differently than old models predicted. And that matters for those designing protective gear or industrial processes where such fluids experience rapid impacts.
If you slowly lower your finger into a cornstarch-water mixture, it will sink in easily, like into thick syrup. But if you punch the surface with your fist, the mixture instantly turns solid and won't let your hand through.