How many times has this happened to you? Pour water on the table and try to empty it from one glass to another or by washing teaspoon Do you see how the water follows the curvature? Instead of falling vertically, as we would like, the water falls flows down the side of the glass. The reason for this phenomenon is no secret, it has an exact name: Coanda effect, named after the French-Romanian physicist who theorized it. This happens with all liquids, more or less visible depending on their density: For example, it also happens with air with the wings of airplanes. This is a behavior that is due to the adhesion and cohesion forces of liquids. However, it can be avoided by increasing the speed at which the liquid is poured. Let's see together what the Coandă effect consists of and in what other cases it can be observed.
Why water doesn't fall vertically: the Coandă effect
The reason we create a mess in these cases is because the water tends to follow the profile of the glass. This behavior is not random, but is due to the Coandă effect: Moving liquids tend to follow the surfaces they come into contact with.
But why is this happening? Because the liquid is “pushed” through the glass onto the glass. Air pressure – which is greater than the pressure that the glass exerts on the liquid – and Adhesive force between liquid and solid. Simply put, the layer of liquid that comes into contact with the glass is forced to stick to the glass. In addition, there are inside the liquid Cohesive forces between the molecules that ensure that the entire liquid follows the profile of the glass and not just the inner layer of the liquid.
How to avoid this effect
Even if it may seem “more dangerous” to us, that Solution Follow the instructions to decant liquids without spilling them on the table Pour them in quickly!
In fact, when pouring slowly, the previously described adhesion and cohesion forces “overwhelm” the other possible forces acting on the liquid, and therefore the water continues to flow over the glass itself. Once it gets over the edge.
However, if we pour it quickly, the other forces “outweigh” the adhesion force. For example, if you pour it quickly, it increases Weight capacity Amount of water, which means more water flows at the same time than if we water slowly. This means that in this case it is The weight force wins over the adhesion forceand so The liquid falls vertically.
Another solution is Choose the right glass for decanting. The Coandă effect also depends on the Surface curvature and be Continuity. The greater the curvature, the sooner the liquid begins to fall downwards.
To make it clear with an example: the edge of the Coffee cups that's enough bent And continuously, So if you're trying to pour coffee from one cup to another, that's a lot difficult don't get drunk. If we use a instead very thin glassits edge is practically free of curvature and will be more simply Pour the water precisely.
If you notice, disposable cups have a special edge: they make a very tight turn and then stop. This shape serves precisely to prevent water from dripping into the glass (and to protect our mouths when drinking).
In what other cases do we see the Coandă effect?
A fun experiment to see the Coandă effect is that of spoon under running water from the sink: If we bring the spoon closer to the water, we will notice that the water that comes into contact with it no longer flows straight, but follows the curved profile of the spoon. We can also notice that as the intensity of the beam increases – and therefore its speed – the effect decreases.
Furthermore, we can see that if we bring the spoon very close without touching the water, the pressure difference and adhesion forces cause the spoon to stick to the water.
There are other, much more complex examples of this effect. Henri Coandă himself observed this while studying aerodynamics, in fact this effect is very clear along aerodynamics Airplane wing.
Another application of this phenomenon takes place in Forum 1In the past, the Coandă effect was used on the body to direct the engine's exhaust gases to the ground and thus increase the aerodynamic load on the car.
