Is it a solid or a liquid?

Today question is easy to understand but kinda hard to answer

Is toothpaste a solid or a liquid?

Easy, right? NO!!! Ok, let's us recap the properties of solid and liquid.

Solid:

1) Have a fixed shape and volume

2) Not easily compressible 

3) Does not flow easily

Particles in solid

4) Particles are tightly packed, usually in a regular pattern.

5) Particles vibrate (jiggle) but generally do not move from place to place.

Liquid:

1) Assumes the shape of the part of the container which it occupies 

2) Not easily compressible

3) Flows easily 

Particles in liquid

4) Particles are close together with no regular arrangement.

5) Particles vibrate, move about, and slide past each other.

Now the question still remains. Is toothpaste a solid or a liquid? If it's a solid, it should have a fixed shape instead of following the shape of the toothpaste tube. If it's a liquid, it should flow out by itself , but we need to push the toothpaste out. Well, it's neither a solid nor a liquid, it's a non newtonian fluid, bingham plastic for exact.

Non newtonian fluid are categorise into three major type, just like matter.

• Shear thickening fluid
• Shear thinning fluid
• Bingham plastic

Shear thickening fluid

The viscosity (thickness) of these fluid change according to the rate of force act on it (Just like stirring). 

For example: Corn starch and water / Sand and water

When we stir the mixture above slowly (low rate of force), the mixture is like liquid. However when we stir vigorously (high rate of force), the mixture act like solid.

Corn starch and water 

Shear thinning fluid

It's a total opposite of shear thickening fluid. That's all I can say.

For example: Hair gel

When we pour the hair gel (low rate of force), it act more like solid cause it hardily flows. However when we rub it between our fingers vigorously (high rate of force), it act more like liquid cause it's easy to rub.

Hair gel

Bingham fluid

These fluids have constant viscosity, but the viscosity is different from solid, liquid and gas.

For example: Molten chocolate syrup

No matter how we stir the syrup, it's still be the same thickness. But it doesn't like liquid

So now the conclusion is "Toothpaste is a Bingham fluid which is a non newtonian fluid." Now we can call it a day! Thanks for paying attention.