In the following post we can see that some guys are walking on Non-Newtonian fluids. As far as I know that, we can not predict the exact amount of strain if we predict some forces. therefore the curve will not be linear. But my question is that, why does Non-Newtonian fluid not obey Newtonian dynamics?
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A Non-Newtonian fluid acts like anything that isn't a Newtonian fluid, so it's a pretty broad category.
In the specific case of oobleck, the type of Non-Newtonian fluid that you can walk on, the resistive force it exerts is proportional to the velocity. So it acts like a dampener in regular mechanics. Push real hard and you will displace faster, but the fluid will offer much higher resistance. If you push softly, you'll move slower but with less resistance.
The deviation from Newtonian behavior happens simply because of internal properties of the fluid. Oobleck is a suspension of water and corn starch. To the best of my knowledge, the way to think of how it's shear thickening behavior arises is that at low velocities, corn start particles are far apart and are 'lubricated' by the water molecules. At higher velocities, the corn starch particles start interacting and chaining together and there isn't enough time for the water to properly lubricate the solution.
Generally for real fluids, the most successful models are a combination of different behaviors. You then find that in a low-velocity or a low-force limit the fluid may behave like a Newtonian Fluid, and in the opposite limit different forces dominate and it exhibits new behavior.
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