Quicksand: science behind the scenes.

Have you ever imagined what you would do if you got trapped in quicksand? Is quicksand a living being? Why does it suck things down? Let’s figure out the ins and outs of this amazing and at the same time weird thing in this new post.

What is quicksand?

First of all, no, it is not a living being who is going to “eat” you. It is a colloid hydrogel, made of a mixture of sand, clay or slit and water. It is mainly formed in areas where there is lots of underground water. This kind of hydrogel is also called a non-newtonian fluid. These fluids get completely different behaviour, depending on the stress you apply to them, as they can change its viscosity (continue reading to know more about non-newtonian fluids). When there is a lot of stress, they behave as a solid: they are tough. However, when there is no stress, it becomes soft and behaves like a regular fluid.

And now, you might be thinking: how can it happen, if sand is not water-soluble? Yes, you are right, if you add sand over a glass of water, after a while, the sand will be in the bottom of the glass. Nevertheless, the phenomenon is a little different.

How is it formed?

When loose sand or other granulated soils mix with water and they form a saturated blend, the water gets trapped. When this colloid is agitated, the soil turns into a liquified area, making water push the sand to the surface. This effect causes the sand to be “quick”. The agitation could come from two phenomena: flowing underground water or earthquakes. The former is more prone to occur. The next chart displays the formation of quicksands.

Quicksand forms when uprising water reduces the friction between sand particles, causing the sand to become "quick."
Formation of quicksand. It forms when uprising water reduces the friction between sand particles, causing the sand to become “quick.” Source: HowStuffWorks

Do you want to make your own quicksand? Click here to learn how or go to the Experiments tab! It’s cheap and easy!

How can I get out of quicksand?

I won’t get deep into this, but if you are interested, here you can learn how to get out of quicksand, step by step and with pictures so you can practise! Just briefly, the density of quicksand is double the density of your body, so if you relax, you will float!

More (about) non-newtonian fluids

Why are they called non-newtonian? It is related to Isaac Newton’s apple? Yes, they are called non-newtonian fluids, because they don’t follow Newton’s law of viscosity. And what is this law about? Newton discovered the viscosity of fluids only depends on temperature so that they become less viscous when heated and more viscous when cooled. Most common fluids, such as water or oil,  are newtonian. However, there are some that don’t follow this law. They can be divided into two groups: shear-thinning (viscosity diminishes when shaken or stirred) and shear-thickening (viscosity increases when stress is applied). Among the former, we find ketchup, shaving cream,  whipped cream, toothpaste, blood, nail polish, syrups and wall paint. However, corn starch and water (“oobleck“), gravy or some body fluids like synovial fluid (the liquid we have in our joints) belong to the latter.

Examples of non-newtonian fluids. Source: Newcastle University

Now, could you now make a guess about which type of fluid quicksand is?





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