Non-newtonian fluid

A Newtonian fluid is the fluid that follows the Newton's laws of motion. (Law of inertia, F=ma, Law of action-reaction). Each Newtonian fluid has the constant fluid viscosity which makes the motion directly proportional to the shear stress applied to it. Consider when one slaps water, a Newtonian fluid, with his hand. If he slaps water lightly, the water wave would merely change. However, when he slaps water hard, the water would splash out (The amount of force is directly proportional to the amount of water reaction). Because of its proportional stress and motion, the motion of the fluid can be calculated through an equation and is easily predictable.

A Non-newtonian fluid is the fluid whose motion for a certain force cannot be explained through Newton's laws of motion. Unlike Newtonian fluid, Non-Newtonian fluid has an irregular motion for a certain force. Consider when one squeezes out ketchup from a ketchup bottle. The squeezed-out ketchup sits still and does not have any movement as if it is a solid. However, when something is dipped into the ketchup (when some force is applied), it readily changes its shape as if it is a liquid. The reason the motion of the fluid is so inconstant is because its fluid viscosity is not constant and therefore, changes its physical properties.





* GRAPH of stress to motion

-> Newtonian fluid draws a linear function (directly proportional force and motion)

-> Non-Newtonian fluid draws a seemingly exponential function (it is actually more complicated than that)

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Non-newtonian experiment with oobleck (cornstarch + water)

Material
1 cup of water

2 1/2 cup of cornstarch

2 containers

1 spoon

1 12 inch speaker

1 straw

Procedure

1. Put 2 1/2 cups 0f cornstarch into a bowl


2. Pour 1 cup of water into the bowl


3. While you are adding the water, stir it slowly. Care should be taken not to stir it too hard because then the suspension of cornstarch and water would become thick and unable to stir.


4. Oobleck is completely made!!


5. Have fun with the oobleck

6. Clean up

Things you can try

• stir it slowly and fast


• deep your finger slowly and then punch really fast


• try to make a ball with it, and then try to hold it


• pour a portion of the oobleck on the table and try to pick it up
  
• put the oobleck on a speaker with maximum amplitude and 60 Hz frequency (To protect the speaker, cover it with a trash bag and then put the oobleck on the bag.)

* Also, try to drop the oobleck from some height and see what happens. Does it make a dull sound as if a solid drops from a distance? Or does it drop as if it is liquid. Why?

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• Different Types of NON-NEWTONIAN fluids

Non-Newtonian fluids are divided into a several different types in the way they behave against force. For example, the motion of oobleck that hardens when a sudden strong force is applied is quite different from that of ketchup that softens when outer force occurs.

-> stress-dependent

1. shear-thickening: Viscosity increases as stress increases (eg. oobleck, ice cream caramel topping)

2. shear-thinning: Viscosity decreases as stress increases (eg. ketchup)

-> time-dependent

1. Rheopectic: Viscosity increases as the duration of stress increases (eg. whipped cream).

2. Thixotropic: Viscosity decreases as the duration of stress increases (eg. honey).

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Real Life Application

According to the research, many countries are studying the properties of Non-Newtonian fluids, especially the shear-thickening property, in order to make body armor. Since shear-thickening Non-Newtonian fluids harden when a sudden strong force is applied, it's been believed that this property would effectively protect the wearer from fast bullets or stabbing knives (As soon as the bullets or the knives touch the surface of the armor, the armor would get hardened). This way, soldiers could move freely and easily with their light armors and yet the armors would be effective enough to stop the bullets before they hurt the wearer.