 # Why are non-Newtonian fluids called non-Newtonian when they follow Newton’s third law? To my understanding, Newton’s third law states that for every action there is an equal and opposite reaction. Therefor if I punch the non-Newtonian fluid harder, there will be a harder reaction force stopping my hand. So why is the fluid called non-Newtonian? owsicag7 2022-07-20 Answered
Why are non-Newtonian fluids called non-Newtonian when they follow Newton’s third law?
To my understanding, Newton’s third law states that for every action there is an equal and opposite reaction. Therefor if I punch the non-Newtonian fluid harder, there will be a harder reaction force stopping my hand. So why is the fluid called non-Newtonian?
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Newtonian fluids are named after Isaac Newton, who first used the differential equation to postulate the relation between the shear strain rate and shear stress for such fluids.
For Newtonian fluids there is a direct proportionality between the two quantities and so for fluids which that is not so are called non-Newtonian.
So just like the three laws of motion, law of gravitation, the rings due to interference of light (Newton first investigated them quantitatively), law of cooling, etc, Newton was (amongst) the first to investigate phenomena quantitatively and thus he is heralded for doing this by having his name used when describing various physical effects.