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A 'non-Newtonian fluid' is a fluid in which the viscosity changes with the applied strain rate. As a result, non-Newtonian fluids may not have a well-defined viscosity.
Although the concept of viscosity is commonly used to characterize a material, it can be inadequate to describe the mechanical behavior of a substance, particularly non-Newtonian fluids. They are best studied through several other rheological properties which relate the relations between the stress and strain tensors under many different flow conditions, such as oscillatory shear, or extensional flow which are measured using different devices or rheometers. The rheological properties are better studied using tensor-valued constitutive equations, which are common in the field of continuum mechanics.

Contents

Common examples

Classification types

See also

External links

Common examples

An inexpensive, non-toxic sample of a non-Newtonian fluid sometimes known as oobleck can be made very easily by adding corn starch (cornflour) to a cup of water. Add the starch in small portions and stir it in slowly. When the suspension nears the critical concentration - becoming like single cream (light cream) in consistency - the so called "shear thickening" property of this non-Newtonian fluid becomes apparent. The application of force - for example by stabbing the surface with a finger, or rapidly inverting the container holding it - leads to the fluid behaving like a solid rather than a liquid. More gentle treatment, such as slowly inserting a spoon, will leave it in its liquid state. Trying to jerk the spoon back out again, however, will trigger the return of the temporary solid state. A person moving quickly and/or applying sufficient force with his feet can literally walk across such a liquid, as shown here and here and here
Shear thickening fluids of this sort are being researched for bullet resistant body armor, useful for their ability to absorb the energy of a high velocity projectile impact but remain soft and flexible while worn.
A familiar example of the opposite, a shear-thinning fluid, is paint: one wants
the paint to flow readily off the brush when it is being applied to the surface
being painted, but not to drip excessively.

Classification types

Kelvin material	"Parallel" linear combination of elastic and viscous effects
Anelastic	Material returns to a well-defined "rest shape"
Time-dependent viscosity	Rheopectic	Apparent viscosity increases with duration of stress	Some lubricants
	Thixotropic	Apparent viscosity decreases with duration of stress	Non-drip paints and tomato ketchup and most honey varieties.
Generalized Newtonian fluids		Stress depends on normal and shear strain rates and also the pressure applied on it	Blood, Custard

See also

★ Newtonian fluid

★ Rheology

★ Viscosity

★ Superfluids

★ Navier-Stokes equations

★ Dissipative particle dynamics

★ Finite deformation tensors

★ Oobleck

★ Quicksand

★ Bingham plastic

External links

★ Viscosity Chart

★ A pool filled with non-newtonian fluid (youtube video)

★ Narrated scientific experiments on the effects of vibrations on a non-newtonian fluid (youtube video)

★ Amateur experiments on the effects of vibrations on a non-newtonian fluid (google video)

★ Cornstarch Lifeforms (youtube video)