If there is something that is a standard of our beaches, it is the walks that we stick along the shore. Now, walking along the beach presents us with a curious paradox: when we lift our foot from the wet sand we see how the sand appears fleetingly dry .
If we stop to think about it a bit, it is intriguing to say the least. When pressing with our feet the sand should react like sponges when we squeeze them: oozing water . But if we look at it, when we lift our feet we do not see that thin layer of water on top of our footprint, but on the contrary, it appears dry. How is it possible?
I recommend that if you are spending your holidays on one of our beaches, do the following experiment: take some sand and put it in a flexible plastic bottle along with some water. Now squeeze the walls: you will watch the water disappear into the sand. This happens because by pressing the sand, the grains are redistributed, which leads to an increase in volume between them. There is more space for the water and therefore more space.
The interesting thing is that this silly observation is very important when it comes to effectively taking advantage of the process of obtaining oil or wine: a higher pressure does not have to produce an extraction of the liquid .
