Science and Tech

Why is water wet? Fluid physics in your life

Why is water wet?  Fluid physics in your life


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

The fluid physics of water

Fluid physics emerged as a formal discipline in the 16th century to contradict some approaches of Aristotle. According to the philosopher, nature did not approve of the existence of a vacuum. But Pascal and others approached the question from the opposite perspective. To scrutinize the absence of matter, one had to study matter itself.

Pascal’s commission to his brother-in-law to climb to the top of an extinct volcano with a pair of mercury barometers he corroborated the experiments on the weight of the atmosphere and the existence of a vacuum carried out by his predecessor Torricelli. And that opened a huge floodgate of knowledge.

Fluids are gases and liquids, both smoke from a chimney and water. They are all substances with such weak forces between their particles that they cannot regain their shape if they lose it.

Water and fluid physics: from toothpaste to Formula 1

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

If we dare to generalize it for fluids in motion, we find, by Bernoulli’s path, the explanation for the ground effect of the Formula 1 racing cars –which makes the vehicle stick to the asphalt to improve its aerodynamics– or how the groundhogs cool their burrows. In fact, those laws apply to any suction process, such as suckle from the tit.

Another environment secularly linked to fluids is medicine. Any anesthesiologist must have a solid understanding of the physics of liquids Y gases to handle catheters or ventilation systems. Doctors were also the Weber brothers, experts in the circulation of the blood, whose magical viscosity makes it flow more slowly near the walls of the vessels, as Pouiseille also showed.


It is the same thing that happens when we move a biscuit over the surface of some custard in a bowl. The less liquid there is in the container, the easier it will be to move. This is also how the tectonic plates when moving 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 the physics of fluids. Another link is Darcy’s law for the passage of a liquid through a porous medium, which can be a sandy soil but also the ground grain of a Italian coffee maker.

Without leaving the kitchen, but returning to viscosity, we still have attractive examples to mention. When the ketchup enclosed in the bottle receives a Accurate blow flows more easily. The paste, along with yogurt, mayonnaise and other viscous foods, goes into non newtoniansso called because they are physically more complex than those with which the great genius delved into this physical subdiscipline when he set out to start it with his wisdom.

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

Why do fluids behave like fluids?

However, the examples given are not excuses to avoid the initial topic. Why does water wet, oil stain and ink stain? It is due to adhesion forces. That is, the affinity between liquid and solid substances.

This translates into the fact that, when putting a fabric in contact with these liquids, they would climb up defying gravity (capillarity phenomenon). But liquids are narcissistic. They feel a tremendous attachment to themselves: the cohesive forces. This generates the so-called surface tension, responsible for the formation of drops of water and other liquids and maintaining their spherical shape. That is worth the worker ants to transport water to their colony.

Will you toast with me to celebrate so much science? Well, then I invite you to observe the tears of wine, another consequence of surface tension. Unfortunately I can only cover the breadth of fluid physics in a few strokes. Saying it, I remember that the fact that the paint be a non-Newtonian fluid allowed to invent the gotelé. But it is not worth getting entangled in nostalgia and putting aside issues of absolute urgency and current affairs.

fluid physics

Fluid physics is essential to explain a wide range of phenomena atmospheric Y oceanographic. And it allows denying that the melting of the North Pole raises the sea level. The argument uses Archimedes’ principle, the same principle that keeps the exploration ships of this scientific field afloat. In this context, I would like to point out that climate change makes flights more susceptible to the phenomenon of turbulence.

But then I would be very tempted to make it visual by resorting to Humphrey Bogart. She would thus take the image of him smoking a cigarette and releasing a column of smoke that becomes a festival of twists and turns. Better give the audience a break. And serve the metaphor to recommend prudence while the covid-19 stay with us. To achieve this goal, fluid physics will continue to brilliantly assist other disciplines and tell us about droplets and their travels.

Font: Ruth Lazkoz / THE CONVERSATION

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