Sand is a granular material composed of grains of minerals such as quartz, feldspar, mica, among others. It can be found in many shapes and sizes, from the large sand dunes of the desert to the fine, soft sand of the beaches.
A phenomenon that many people have experienced is the feeling that sand sticks on everything, especially on skin and clothes. But why does this happen?
The answer lies in the physics of granular materials. When a grain of sand comes into contact with a surface, it can adhere to that surface due to the frictional force between the two materials.
In addition, the shape of the sand grains also contributes to this adherence. Sand grains are generally angular and irregular, which means they fit together and on other surfaces more effectively than softer shaped grains.
Another factor that contributes to the adhesion of sand is humidity. When sand is wet, it clumps together and forms small liquid bridges between the grains, which increases the adhesion strength. As a result, wet sand is even more likely to stick to surfaces.
In addition, static electricity can also contribute to sand sticking. When sand is moved, it can become electrified, generating an electrical charge that can attract more grains of sand and other particles. This may explain why sand often seems to stick together more on dry, low-humidity days.
Another explanation for sand adhesion is the surface tension of liquids. When we are at the beach, sea water wets the sand and creates a thin layer of liquid on the surface. This layer of liquid creates surface tension that can cause sand to stick to our skin or other surfaces.
Finally, it is important to remember that the adhesion of sand varies according to the characteristics of the grains of sand and the surfaces in contact with it. For example, smooth, low-porosity surfaces tend to hold less sand than rough, porous surfaces. Also, different types of sand, such as beach sand and desert sand, can have different levels of adhesion.
This is why sand sticks to everything due to a combination of physical factors such as frictional force, the shape of sand grains, humidity, static electricity and the surface tension of liquids.
While it can be frustrating to have sand sticking to our clothes and skin, it's important to remember that this property of sand is also what allows for the formation of impressive natural structures, such as desert dunes and beach sand cliffs.
