Surface tension and longevity bubbles
British experimental physicist Boyce, who designed perhaps the most widely publicized soap bubble experiment.
During Christmas 1889, he gave several public lectures, showing teenagers the soap bubble experiment. One of the experiments went like this: put a ring in soapy water and make it form a soap film; if you tie a thread in the ring (and one of the lengths is a double thread), three films are formed , pierce the membrane in the double line, and the area wrapped by the double line naturally forms a circle.
Two lines are drawn into a circle contains mathematical and physical knowledge
This experiment visually demonstrates the process by which surface tension minimizes the surface area of a liquid, which is why airborne soap bubbles are spherical.
But surface tension is much more than that for soap bubbles—it’s the lifesaver of soap bubbles. When the liquid film of the soap bubble is disturbed and locally thinned, the surface tension in this part of the region will increase, and a greater pulling force will be exerted on the surrounding liquid. As a result, the liquid will be naturally pulled towards the thinned area, completing self-healing. This phenomenon is called the Maragoni effect.
James Dewar, a pioneer in the study of cryogenic gases, is famous for inventing the Dewar flask to hold liquid air. For the last 20 years of his life, he immersed himself in the study of the surface tension of soap bubbles. Dewar has set an astonishing record of keeping a single bubble for three years by carefully preserving it in a special bottle to reduce contact with air impurities.
Newton is everywhere
But the most fascinating thing about soap bubbles is the changing colors.
Why is the foam in the sun colored? The answer to this question comes from Newton.
Newton’s life was brilliant, and mathematics, mechanics, optics, and astronomy blossomed in an all-round way. Among its optical achievements, there is a research result called “Newton’s rings”, which can explain why the bubbles are colorful.
Spatial arrangement of multiple truncated octahedra
The soap film itself is colorless. Sunlight composed of visible light of different wavelengths is reflected on the upper and lower surfaces of the soap film and interferes. If in a certain part of the film, the red light in the two beams of reflected light cancels each other out, then there is blue-green; in another place, the red light may be strengthened. In addition, the thickness of the soap film is not uniform, and with the disturbance of airflow and gravity, the film thickness will also change all the time. As a result, the entire soap bubble presents a constantly changing multicolored. This phenomenon occurs on the surface of oil films floating on the water or on the surface of pearls.
The Old Lord’s Question
Of course, Newton didn’t discover Newton’s rings by blowing bubbles. However, many scholars have discovered a new world in blowing soap bubbles.
The founder of thermodynamics, the British physicist Lord Kelvin, is one of them.
Kelvin once said: “If you blow a soap bubble and observe, you can study it for a lifetime, and get from it one law of physics after another.” In 1887, Kelvin’s niece went to the country to visit the old Sir. Opening the door, the picture in front of him is the great scholar blowing bubbles happily.
Lord Kelvin, who was obsessed with soap bubbles, once asked a question: If the space is divided into many parts to ensure the smallest contact area, what shape should these parts be? This problem was later known as the “Kelvin problem”.
In a two-dimensional plane, the Kelvin problem has been solved by bees. The hexagonal honeycomb structure is the most efficient stacking method on the plane. Of course, bees have no mathematical basis, they build their nests just to save some beeswax – this is the wisdom of nature!
As for the Kelvin problem in three-dimensional space, the answer given by the old Lord himself is the truncated octahedron, which consists of eight regular hexagons and six squares. Kelvin believes that filling space with this structure is most efficient. This answer was apparently inspired by soap bubbles.
Will-Fran bubble structure
Beyond Kelvin – The Will-Frank Bubble
In 1993, Kelvin’s bubble burst.
Irish physicists Dennis Weir and Robert Forlan have proposed a new design that goes beyond the Kelvin structure.
The structure, called a Will-Fran bubble, contains two types of cells: 12-sided and 14-sided. Filling the space with Will-Fran bubbles can save 0.3% of the raw material compared to the Kelvin method.
The Will-Fran bubble was the inspiration for the design of the Beijing Olympic Swimming Center (Water Cube). Because of this model, the amount of steel required for the “Water Cube” has been greatly reduced, and the entire main body of the building was built with only 6,700 tons of steel.
However, whether the Will-Fran bubble is the final solution to the “Kelvin problem”, we can’t make a conclusion now, and we can only hope that the scientists blowing bubbles will do their best.
The Water Cube borrows from the Will-Ferran bubble model
Prato also has a problem
Like Kelvin, the Belgian physicist Prato is also a master of blowing soap bubbles. He even wrote a 450-page monograph on bubbles, “Hydrostatics and Experiments under Molecular Forces Only” ( 1873). Prato also found a problem in blowing bubbles: how to find the minimum surface mathematically given the boundary curve. This problem is also named “Plato problem”.
To answer this question requires a lot of advanced theory involving geometry. But in life, as long as you take a wire and bend it into a boundary, dip it in soapy water, and the bubbles you blow are the solution to the Prato problem.
Of course, scientists will not be so satisfied, they are eager for rigorous proof from mathematics, and even developed the Prato problem to a high-dimensional space. This search for “minimum surfaces” attracts batch after batch of brilliant minds.
In 2019, the Abel Prize, known as the “Nobel Prize in mathematics”, was awarded to American mathematician Karen Uhlenbeck. As one of the founders of modern geometric analysis, Uhlenbeck is best known for his work on minimal surfaces. Who knows, maybe she’s blowing bubbles in private too.
Scientists have never stopped researching soap bubbles.
The scientific problems that extend from the bubble are not limited to mathematics and physics. Biofilms similar to soap films, foam structures in material science, and inflatable film structures in engineering science… are all worthy of a lifetime of research.
The scientific problems that researchers think about day and night and the colorful sounds blown out by children in the summer afternoon are equally worthy of pursuit and appreciation.