A really strange liquid… or not!!!
Cornstarch Oobleck
Dilatant Fluids – Non‐Newtonian behaviour
Viscosity – Resistance to flow offered by a liquid. It is the ratio of shearing stress
experienced by the liquid over the velocity of its flow.
Newtonian fluids
Shear stress is proportional to the
strain. Viscosity doesn’t depend on the
strain applied.
Example :– Water, Ethanol
Non ‐ Newtonian fluids
Shear thinning fluids
Shear Stress
Shear stress experienced by the liquid
increases with the strain (Force)
applied. The rate at which this
increases with strain depends on the
nature of the liquid.
Newtonian fluids
Shear thickening fluids
Shear Strain Rate
Pseudoplastic (Shear thinning) fluids – The rate of increase of shear stress decreases
with applied strain. Apparent viscosities decrease as you increase the strain.
Example :‐ Ketchup, Drip‐free‐paint, Toothpaste.
Thumping hard on the backside of a ketchup bottle in principle should help!!!
Dilatant (Shear thickening) fluids – The rate of increase of shear stress increases
with applied strain. Apparent viscosities increase as you increase the strain.
Example :‐ Cornstarch Suspension, D3O liquid armor.
Thank goodness your toothpaste doesn’t freeze to a solid when you squeeze the
tube in the morning!!!
And why does it do that???
In low strain, the water flows freely between the particles of the cornstarch and is
able to flow. But when you apply strain, we have higher particle to particle
interaction. The higher interaction causes a higher viscosity. It appears to form a
solid because after a limit, the movement of the water is restricted just to the
interstitial spaces between the particles.