Table of Contents

## Introduction

Sir Isaac Newton is famous for the development of several important scientific theories in the fields of physics as well as mathematics.

He described Newtonian fluids which are normal liquids that had a constant viscosity. The Newtonian fluids had a fixed viscosity or flow quality in a given temperature and an atmospheric pressure. Within the temperatures of 0˚C and 100˚C which are the melting point and the boiling point of the water respectively, water has a constant viscosity.

Newtonian fluids are the most basic mathematical representations of liquids that take into account viscosity. Whereas no actual fluid exactly meets the criteria, many prevalent liquids and gases, such as water and air, can be considered to be Newtonian fluids. Non-Newtonian fluids, on the other hand, are rather prevalent.

## What is viscosity?

The measure of a fluid’s resistance to flow. The viscosity of thick slow-flowing liquids is high, while the viscosity of thin fast-flowing liquids is low.

## What is force?

A push or pull which affects an object’s form, direction, and/or movement to change. Force is measured in Newton (N)

## What is pressure?

Force applied per unit area of the surface of an object is called the pressure. Pressure is measure in Newtons per square meter.

## Different types of non-Newtonian fluids

When stressed, not all non-Newtonian fluids react the same way; some become more solid, while others become more fluid. The characteristics of non-Newtonian fluids may change depending on the amount of stress applied or else on the duration the stress is applied. Due to different characteristics of these non-Newtonian fluids, they are categorized into several groups.

1. Thixotropic – this means the fluid behaves like a solid when it is kept still and becomes liquid when shaken. In other words, the viscosity of the fluid decreases when stress is applied for a prolonged duration of time. Honey is a perfect example for this. When stirred continuously honey becomes more liquid in its character. Yoghurt, peanut butter and most gels act in this manner. Thixotropic is a type of time dependent viscosity.
2. Rheopectic – this means the fluid acts as a liquid but when stress is applied it becomes more solid. In other words, the viscosity of the fluid increases when stress is applied for a prolonged time duration. Cream and gypsum paste are common examples for this kind of non-Newtonian fluid. When stress is applied continuously these fluids become more solid in its behavior. Rheopectic is a type of time dependent viscosity.
3. Shear thinning – this means the viscosity of the fluid decreases with powerful stress. It is the amount of stress that matters rather than the duration. Nail polish, ketchup, blood and silicone oils are different examples for shear thinning non-Newtonian fluids.
4. Shear thickening or dilatant – this means the viscosity increases with powerful stress. It is the amount of stress that matters rather than the duration. Cornstarch in water (known as oobleck) is a popular example for dilatants.

## Non-Newtonian fluid oobleck / cornstarch?

Cornstarch solution also known as oobleck is a non-Newtonian fluid which means its viscosity depends of the stress applied to it. Newtonian fluids on the other hand are the liquids that have a constant viscosity in a given temperature and atmospheric pressure.

Oobleck is made from mixing cornstarch with water. When you grasp it in a ball, it feels solid, but when you let go of your hand, it turns liquid. It adopts to the form of the container around it.

Dr. Seuss’s novel, Bartholomew and the Oobleck, inspired the term Oobleck. The oobleck is a mysterious material that falls from the sky in it.

## How non-Newtonian fluids work?

Newtonian fluids have a constant viscosity in a given temperature and atmospheric pressure setting. Non-Newtonian fluids have a variable viscosity that usually depends either on the amount of stress applied or the duration the stress is applied.

Depending on the characteristics non-Newtonian fluids can be classified as thixotropic, rheopectic, shear thinning and shear thickening. Let’s see how these mechanisms work in illustrated diagrams.

## How to make a non-Newtonian fluid?

Let’s see a non-Newtonian fluid recipe. We are going to make cornstarch solution which is known as oobleck.

### What you need to make oobleck

• A mixing bowl
• 2 cups of cornstarch
• 1 cup of water
• Food coloring

### How to make oobleck

1. Take the mixing bowl and add 2 cups of cornstarch
2. Add food coloring to 1 cup of water and mix it
3. Slowly add the cup of water while mixing with hand
4. Mix the contents well until it has a honey-like viscosity
5. Now you can study the characteristics of a non-Newtonian fluid

## What are the uses of non-Newtonian fluids?

Well, it is diverse. Can you list all the uses of cosmetics, toothpaste, butter, jam, yoghurt, gums, honey, blood and emulsions? The uses actually depend on the specific non-Newtonian fluid we are referring to.

But in advanced science non-Newtonian fluids can be used for specific functions due to their characteristics. Body armor used in the military is a perfect example. It is lightweight and acts as a solid on sudden stress. So, it is hard and light weight at the same time.

Certain types of building material act in dangerous ways in natural disasters. Understanding the behaviors of non-Newtonian fluids is essential when choosing building materials.

## Non-Newtonian fluids Q&A time!

### Is Lava a non-Newtonian fluid?

Yes. Lava and magma act as non-Newtonian fluids.

### Is Glass a non-Newtonian fluid?

Glass is shown to have solid properties, so glass is not a non-Newtonian fluid.

### Is Blood a non-Newtonian fluid?

Biological fluids like blood and saliva are non-Newtonian fluids.

### Is Ketchup a non-Newtonian fluid?

Yes. Ketchup has characteristics of a non-Newtonian fluid.

### Is Slime a non-Newtonian fluid?

Yes. Slime has a variable viscosity that relies on stress applied to the material therefore making it a non-Newtonian fluid.

## Conclusion

Fluids can be studied as Newtonian fluids and non-Newtonian fluids. Non-Newtonian fluids can be further divided into four groups depending on their behavior. Non-Newtonian fluids exist in nature and scientists investigate their qualities in order to develop novel solutions that may be employed for a variety of purposes.

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