Eli5 why does wet sand stick together?



Eli5 why does wet sand stick together?

In: Earth Science

Sand particles are quite small, so they have a relatively low volume/mass compared to their surface area (square-cube law). That’s important.

Water undergoes strong cohesive (which is responsible for surface tension) forces with itself due to hydrogen bonds, and it also has strong adhesive (sticking) forces as a result of induced interactions with silicon dioxide – also called wetting. These forces help the light sand particles to stick together, especially when you look at the scale where water is extremely effective for this purpose – as opposed to say ball bearings, pebbles, or golf balls.

Damp sand sticks together because water forms little grain-to-grain bridges. Surface tension–the same force that lets some insects walk on the surface of a pond–acts like rubberbands between the grains. Adding water to damp sand fills spaces between the grains. The bridges vanish and the sand begins to flow more easily.

Pretty much only because of water. 1) cohesion, 2) surface tension. Sand itself isn’t a very sticky substance (relative to clay and silt) because it is largely inert and doesn’t have many exhange sites (if at all) for other molecules/nutrients/whatever to bind

Because water sticks to water, and water sticks to sand. And because sand is rough and hard, and doesn’t slip past itself (it rolls instead), the combination can’t move much, so it’s stronger than just the sticky water.