What State Of Matter Is Sand ?

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When it comes to matter, we have basically four states of matter namely, solid, liquid, gas and plasma. There are others but they aren't very obvious or common. However, there are substances which are also matter but don't fall into any of the conventional states of matter (including those other forms of matter that aren't obvious or common), an example being sand.

Hold on.......... I don't mean a grain of sand, we all know it's solid. What we are actually discussing is the kind we see more often, grains of sand - as a collective. When you pick up sand, you don't pick up a grain, you pick up grains. So, for the remainder of this article, when we discuss about sand, we talking about it as a collective - not a single grain. Now, sand (grains) is also matter but they belong to a kind of matter classified as "granular materials", another example is powder. But unfortunately, "granular materials" isn't a form of matter according to current classifications of matter states and if they aren't, then what state of matter do they belong to ?

It's actually quite complicated. When different gases come together, assuming there isn't a chemical reaction, the resulting product is a "mixture of gases" which still happens to be in the gaseous state - air is an example. Applying the same principle to liquids you have the same, that is, a mixture of liquids which collectively is still liquid. However, try applying the same principle to solids and you are likely to be wrong, especially when the solids are of uncountable amounts. Let's look at sand which happens to be the main focus of this article.

Sand which happens to be made of many solid particles can take the shape of a container - a macroscopic property of liquids. Have you watched when sand is poured from a container, especially in a construction site ?

What do you notice?

It moves like a liquid, technically, it's flowing - a macroscopic property of fluids (liquid and gas). So, do we say that sand is liquid?

I think you may need to rethink. Ok, why do I say so ?

Sand too can have a definite shape, you must have seen a pile/heap of sand before - probably in a construction site, apparently there isn't any container giving it that shape. The fact is that, sand like all other granular materials are very complicated systems, they can display all three (solid, liquid and gas) properties and even novel properties not found in the conventional states of matter, depending on certain conditions. In a dynamic setting, sand displays fluid characteristics, when you look at sand being poured, it's in a dynamic setting and therefore you see it flowing.

Sand too can display gaseous properties, this also happens in a dynamic setting. Put sand in any container, the container shouldn't be filled completely - there should be lots of space remaining, close the container and shake it rigorously, what do you notice?
The sand not only takes the shape of the container but the particles become very far apart from each other and distribute themselves to fill nearly all the spaces in the container and surprisingly this is how gases normally behave (regardless of shaking the container).

In a static setting it can display both properties of solid and liquid. When in a container at rest can take the shape of the container and when not in a container can take a definite shape, like in the case of a heap/pile of sand. This is so because of the state of the "sheer stress".

Another reason why you can't really classify sand as a liquid (especially Newtonian liquids) is when it's in a static state in a container. Imagine a tank of water (with an opening close to the bottom), actually this is how conventional tanks are designed (with tap at the bottom). If you notice, when the height of the water reduces, the water runs/flows more slowly or the greater the height of water, the higher the flow from the tap. This is actually a principle/law in hydrodynamics (Torricelli's law) and it's kinda related to Bernoulli's principle, in a uniform gravitational field, the greater the height of the liquid, the greater the pressure at the bottom and in turn the greater the flow/velocity. From Torricelli's principle one can get Stevin's law, which is that the pressure at the bottom of a cylindrical tank filled with water depends on the height of the water (in a uniform gravitational field). Unfortunately, if you happen to replace water with sand in the tank, Stevin's principle doesn't hold, the principle for sand is very different, it appears to follow what is called a "Janssen Effect".

There are more reasons why sand can't be given a specific state of matter, the ones presented in this article are the less technical and very familiar ones. But this doesn't mean it may never have, it appears apparently that's the least of scientists worries, there are a lot of things yet to be figured out, especially those regarding complex systems. Also remember in one of my previous articles we discussed about the same difficulty assigning a state of matter to living things (especially cells) - we are also complex systems. I believe only time would tell.

Ok guys, this is where we conclude this article have a thoughtful day and see you when next we meet again - online.

For further reading

Granular material

State of matter

Solid

Liquid

Torricelli's law

Thank you all once again for stopping by to read my jargons and also thank you @stemng, @lemouth and the @Steemstem team for your valuable supports.

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