Normal Newtonian fluids such as water flow at a rate directly proportional to the pressure applied โ the greater the pressure, the faster it flows. However, there is a class of materials called non-Newtonian fluids that break this rule in a dramatic and surprising way.
Oobleck โ a simple mixture of cornstarch and water in a 2:1 ratio โ is the most famous example of a non-Newtonian fluid. At first glance, it looks and feels like a regular thick liquid. However, when you try it, you find that it behaves as if it has a life of its own.
When you slowly dip your hand into oobleck, it flows like a normal liquid and your hand goes in without any problem. However, if you try to dip your hand quickly โ or hit the surface of the oobleck โ it suddenly behaves like a hard solid. You can stand or run on a large pool of oobleck without sinking, as long as you keep moving โ but if you stop, you will slowly sink.
This phenomenon occurs because of the cornstarch particles in the water. When pressure is applied slowly, the particles have time to move out of the way, allowing the material to flow. However, when pressure is applied quickly, the particles become 'trapped' between each other and do not have time to move โ the mass of the particles blocks the flow and the material responds like a solid.
Non-Newtonian fluids have many useful applications. Safety suits that use non-Newtonian fluids become hard when a hard object hits them (absorbing the impact) but are flexible under normal conditions. Liquid armor, sports protection, and electronic protectors all use this principle.