And Friday is here again, bringing with it the weekly column "A Taste of Physics" — issue #43.
This time: surface tension, the Laplace and Plateau laws, and how all of this relates to… soap bubbles!
-
Soap bubbles are a fascinating thing.
Their fragile, perfect structure, their gentle floating, and the swirling colors they display make them a joy to watch at any age.
But soap bubbles are also a captivating example of a long list of interesting physical phenomena.
-
The common thread running through these phenomena is that a physical system always tends to minimize its energy.
Of course, this isn't a conscious decision on nature's part — it's a process driven by energy loss to the surroundings, much like a cup of tea cooling down when left in the open air.
-
A bubble forms due to the phenomenon of surface tension.
Surface tension arises because molecules near the surface are not pulled upward toward the air, unlike interior molecules, which are pulled in every direction.
The spherical shape of a bubble emerges because it is the shape with the lowest possible potential energy.
-
Smaller bubbles tend to collapse into larger ones, and the reason lies in a complex mathematical equation known as the Laplace equation.
According to this equation, the smaller the bubble, the greater the outward air pressure inside it — and so it merges with the larger bubble in order to reach the lowest possible total energy.
The reason smaller bubbles carry excess energy is that the smaller the bubble, the greater its curvature, and therefore the inward pressure is distributed across fewer molecules.
If you've ever wondered why inflating a birthday balloon is hardest on the first breath, now you know why.
-
Plateau's laws define the contact angles between soap bubbles in a foam.
They show that the junction of three bubbles always occurs at a precise angle of exactly 120 degrees.
Here too, the reason is that this arrangement is the most energetically efficient.
The same relationship can be found in a honeycomb — the hexagonal shape arises from 120-degree angles at the junction points, making it the most efficient possible structure.
-
The fact that molecules "know" how to arrange themselves independently is profoundly significant.
It can be found in some particularly remarkable places, such as the folding of proteins in the human body into complex three-dimensional structures.
Shabbat Shalom 😊
#ATasteOfPhysics