## Friday, March 2, 2012

### Oobleck Recipe

Recipe For Oobleck:

- 1 cup water
- 2 cups corn starch
- Few drops of food coloring of your choice (We used blue)

Oobleck is a Non-Newtonian Fluid that got it's name from the book titled Bartholomew and the Oobleck written by Dr. Seuss. But what is a Non-Newtonian Fluid you might ask? Here is a brief explanation I found on wikipedia.com.

A non-Newtonian fluid is a fluid whose flow properties differ in any way from those of Newtonian fluids. Most commonly the viscosity(resistance to deformation or other forces) of non-Newtonian fluids are dependant on shear rate or shear rate history. However, there are some non-Newtonian fluids with shear-independent viscosity, that nonetheless exhibit normal stress-differences or other non-Newtonian behaviour. Many salt solutions and molten polymers are non-Newtonian fluids, as are many commonly found substances such as ketchup, custard,toothpaste, starch suspensions, 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, and can even be time-dependent. Therefore a constant coefficient of viscosity cannot be defined.
Therefore, 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 which 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.

Got that? Me neither! But once you mix up the above concoction I assure that you and your children will have a much better understanding of what a Non-Newtonian fluid is!