Fluids in Physics

When you think of a "normal" liquid you think of one that you can pour into a glass and it will take the shape of the glass. These are called Newtonian fluids. But there are fluids that don't behave like this -- referred to as Non-Newtonian fluids.

Non-Newtonian fluids change their viscosity or flow behaviour under stress. If you apply a force to such fluids (say you hit, shake or jump on them), the sudden application of stress can cause them to get thicker and act like a solid, or in some cases it results in the opposite behaviour and they may get runnier than they were before. Remove the stress (let them sit still or only move them slowly) and they will return to their earlier state.

ScienceLearn

This causes some very odd behavior which you don't typically expect from a liquid. There are a few different types of Non-Newtonian fluids and they each behave slightly differently. Honey, if it's been sitting a while, tends to harden. If you constantly stir it, it will eventually get smoother and becomes more and more liquid-like. Another example of a Non-Newtonian fluid is referred to as Oobleck. Oobleck has recently been going around social media as it is very entertaining for people to play with. When poured slowly it behaves like a liquid; on the other hand if it is striked fast and hard it reacts as if it is a solid. This allows you to run across it without falling through or to hit it with a hammer and not have it splash everywhere.