A non- Newtonian fluid is a fluid that does not follow Newton's Law of Viscosity. Most commonly, the viscosity (the gradual deformation by shear or tensile stresses) of non-Newtonian fluids is dependent on shear rate or shear rate history. Some non-Newtonian fluids with shear-independent viscosity, however, still exhibit normal stress-differences or other non-Newtonian behavior. Many salt solutions and molten polymers are non-Newtonian fluids, as are many commonly found substances such as ketchup, custard, toothpaste, starch suspensions, maizena, honey, paint, blood, and shampoo. In a Newtonian fluid, the relation between the shear stress and the shear rate is linear, passing through the origin, the constant of proportionality being the coefficient of viscosity. In a non-Newtonian fluid, the relation between the shear stress and the shear rate is different. The fluid can even exhibit time-dependent viscosity. Therefore, a constant coefficient of viscosity cannot be defined. Although the concept of viscosity is commonly used in fluid mechanics to characterize the shear properties of a fluid, it can be inadequate to describe non-Newtonian fluids. They are best studied through several other rheological properties that relate stress and strain rate tensors under many different flow conditions—such as oscillatory shear or extensional flow—which are measured using different devices or rheometers. The properties are better studied using tensor-valued constitutive equations, which are common in the field of continuum mechanics.
1 Types of non-Newtonian behaviour
2.1 Oobleck 2.2 Flubber 2.3 Chilled caramel topping 2.4 Silly Putty 2.5 Plant resin 2.6 Ketchup 2.7 Dry granular flows
3 See also 4 References 5 External links
Types of non-Newtonian behaviour Summary
Classification of fluids with shear stress as a function of shear rate.
Comparison of non-Newtonian, Newtonian, and viscoelastic properties
Viscoelastic Kelvin material, Maxwell material "Parallel" linear combination of elastic and viscous effects Some lubricants, whipped cream, Silly Putty
Soap solutions, cosmetics and toothpaste Food such as butter, cheese, jam, ketchup, mayonnaise, soup, taffy, and yogurt Natural substances such as magma, lava, gums, honey, and extracts such as vanilla extract Biological fluids such as blood, saliva, semen, mucus and synovial fluid Slurries such as cement slurry and paper pulp, emulsions such as mayonnaise, and some kinds of dispersions
Demonstration of a non- Newtonian fluid at Universum in Mexico City
Oobleck on a subwoofer. Applying force to oobleck, by sound waves in this case, makes the non- Newtonian fluid thicken.
An inexpensive, non-toxic example of a non-
Newtonian fluid is a
suspension of starch (e.g. cornstarch) in water, sometimes called
"Oobleck", "ooze", or "magic mud" (1 part of water to 1.5–2 parts of
corn starch). The name "oobleck" is derived from the Dr.
Seuss book Bartholomew and the Oobleck.
Because of its properties, oobleck is often used in demonstrations
that exhibit its unusual behavior. A person may walk on a large tub of
oobleck without sinking due to its shear thickening properties, as
long as the individual moves quickly enough to provide enough force
with each step to cause the thickening. Also, if oobleck is placed on
a large subwoofer driven at a sufficiently high volume, it will
thicken and form standing waves in response to low frequency sound
waves from the speaker. If a person were to punch or hit oobleck, it
would thicken and act like a solid. After the blow, the oobleck will
go back to its thin liquid like state.
Main article: Flubber (material)
Flubber is a non-Newtonian fluid, easily made from polyvinyl
alcohol–based glues (such as white "school" glue) and borax. It
flows under low stresses but breaks under higher stresses and
pressures. This combination of fluid-like and solid-like properties
makes it a Maxwell fluid. Its behaviour can also be described as being
viscoplastic or gelatinous.
Chilled caramel topping
Another example of this is chilled caramel ice cream topping (so long
as it incorporates hydrocolloids such as carrageenan and gellan gum).
The sudden application of force—by stabbing the surface with a
finger, for example, or rapidly inverting the container holding
it—causes the fluid to behave like a solid rather than a liquid.
This is the "shear thickening" property of this non-Newtonian fluid.
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.
Main article: Silly Putty
Bingham plastic Caramel Complex fluid Dilatant Dissipative particle dynamics Generalized Newtonian fluid Herschel–Bulkley fluid Navier–Stokes equations Newtonian fluid Pseudoplastic Quicksand Rheology Superfluids Weissenberg effect Thixotropy
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