“El agua moja” is a phrase used synonymously with the obvious. But can we explain why? It’s time to visit this and many other everyday phenomena using fluid physics.

Fluid physics emerged as a formal discipline in the 16th century to contradict some of Aristotle’s approaches. According to the philosopher, nature did not approve of the existence of a vacuum. Pascal and others, however, approached the question from the opposite angle. To study the absence of matter, it was necessary to study matter itself.

Pascal’s order for his brother-in-law to climb to the top of an extinct volcano with several mercury barometers confirmed the experiments on the weight of the atmosphere and the existence of a vacuum carried out by his predecessor, Torricelli. And this opened up a great flood of information.

Fluids are gases and liquids, which are both smoke and water coming out of the chimney. All are substances with such weak forces between their particles that they cannot regain their shape if lost.

From toothpaste to Formula 1

But where can we find fluid physics in our daily routines? For example, in the way pressure changes are transmitted between two points in a fluid. With this we manage to get the toothpaste out of the tube using the same principle that makes the syringe and hydraulic brakes work.

If we dare generalize this to moving fluids, along Bernoulli’s path, we find an explanation of the ground effect of Formula 1 race cars—which makes the car stick to asphalt to improve its aerodynamics—or how marmots cool their nests. In fact, these laws apply to any sucking process, such as sucking from the breast.

Another medium earthly connected with liquids is medicine. Any anesthesiologist must have a solid understanding of the physics of liquids and gases to operate catheters or ventilation systems. The doctors were also the Weber brothers, who, as Pouiseille demonstrated, were experts in blood circulation, whose magic viscosity makes blood flow more slowly near the walls of the arteries.

The same thing happens when we run the biscuit over the surface of the pudding in a bowl. The less liquid in the container, the easier it is to move. This is also how tectonic plates behave as they move over the Earth’s mantle, one of many applications of fluid physics to geology. It is interesting that both sciences go hand in hand with everyday life through fluid physics. Another connection is Darcy’s law for the passage of a liquid through a porous medium; This could be a sandy ground, or it could also be the ground grain of an Italian coffee pot.

Returning to viscosity without leaving the kitchen, we still have some attractive examples to mention. The ketchup in the bottle flows more easily when it receives an accurate hit. With paste, yogurt, mayonnaise and other sticky foods non-NewtoniansThey are so named because when the great genius decides to begin this physical subdiscipline with his wisdom, they are physically more complex than he entered this subdiscipline.

Between stoves it is easy for us to experiment on the effect of physical conditions on liquids in general. It is very obvious when we observe that honey flows more easily when heated. This again tells us how many edges to cover when investigating fluid physics.

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Why do liquids behave like liquids?

But the examples given are no excuses to avoid the topic at the beginning. Why does water get wet, oil stains and ink stains? It is due to adhesion forces. That is, the affinity between liquid and solid substances.

This means that when bringing a fabric into contact with these liquids, they will defy gravity and climb up (the phenomenon of capillarity). But liquids are narcissistic. They feel a tremendous attachment to themselves: unifying forces. This produces the so-called surface tension, which is responsible for the formation of water drops and other liquids and maintaining their spherical shape. Worker ants use it to carry water to their colonies.

To celebrate all this science, will you toast with me? So I invite you to observe the tears in wine, another consequence of surface tension.

Unfortunately I can only cover the breadth of fluid physics in a few strokes. Having said that, I remember the fact that paint is a non-Newtonian fluid led to the invention of gotelé. But it is not worth getting into nostalgia and setting aside absolute urgency and current affairs.

Fluid physics is essential to explain a wide variety of atmospheric and oceanographic phenomena. And it allows to deny that melting glaciers raises sea levels. The argument uses the Archimedean principle, the same principle that keeps ships of exploration in the scientific field afloat. In this context, I would like to point out that climate change makes flights more sensitive to turbulence.

But then I would turn to Humphrey Bogart and be very keen to visualize it. So he would release his image as he smoked a cigar and a column of smoke that became a festival of twists and turns.

You’d better give the audience a break. And serve the metaphor to suggest caution while covid-19 is still among us. To achieve this goal, fluid physics will continue to help other disciplines brilliantly and teach us about droplets and their journeys.

Ruth Lazkoz, Professor of Theoretical Physics, University of the Basque Country / Euskal Herriko Unibertsitatea

This article was originally published on The Conversation. Read the original.