The Science behind Bubbles
Author: Navya Nair
From: Trivandrum, India
We’ve all been there at one point - a visit to the sink to wash your hands turns into a passionate observation of the soap bubbles you can blow with them. But little do most people know, bubbles serve not only as entertaining playthings but also as incredibly powerful scientific tools. They are a perfect example of the brilliant intersection of scientific concepts such as light, surface tension, and molecular chemistry in everyday life. Not only this, bubbles have profound effects on our natural world, be it in the circulation of organic matter in the ocean or the taste of champagne. In this article, we’ll discuss some of the fundamentals of bubble science and its applications.
First and foremost, let us establish the two different kinds of bubbles - soap bubbles and bubbles in a liquid.
A soap bubble is likely the kind that you imagine when you hear the word bubble. It consists of a thin spherical film of soap encapsulating air or gas. The soap film itself is made up of one water molecule sandwiched between two soap molecules. The soap molecules are arranged such that the hydrophilic (attracting water) side of each molecule lies towards the water while the hydrophobic (repelling water) side faces away from the water, towards the surface.
Half of what makes soap bubbles as beautiful as they look are the rainbow colors that swirl around their surfaces. But how does this work? Well, bubbles get their color from white light, which contains every color of the rainbow. Every color in the electromagnetic spectrum corresponds to a certain frequency. If you imagine a leaf suspended in a still pond, the number of times the leaf bobs up and down after a disturbance is created in the water is equal to the frequency of waves in the pond. In the case of light waves, frequency represents how many wave vibrations there are in a second.
When white light enters a bubble, light waves reflect from the outer soap layer to the inner one repeatedly. This inevitably causes some of the waves to interfere, resulting in their frequencies combining. Since each frequency corresponds to a different color, the newly formed frequencies make the colors on the bubble surface change. These are called interference colors.
Whether you are blowing bubble solution through cupped hands or oddly-shaped wands, the bubbles we blow always end up being spherical. This is entirely due to a property of water called surface tension, which pulls molecules of liquid as tightly together as possible to minimizes the surface area of the structure. Compared to any other shape, a sphere has the least surface area for the volume inside of it, and therefore, takes the least amount of energy to achieve. This is why no matter what shape a bubble has initially, it will try to become a sphere.
Soap films have also proven to be invaluable for scientists in studying the flow of fluids in otherwise inaccessible situations. For instance, the storms in Jupiter's atmosphere can be studied by recreating that same flow on the surface of a bubble.
Storms in Jupiter’s atmosphere
Bubbles in liquid
These are small balls of gas that appear within a liquid. When breaking waves drag air underwater at sea, millions of underwater bubbles are formed. The immense plumes of air bubbles trapped in the water create a new mixture much more substantial than air but considerably less dense than water.
Plumes of underwater bubbles
Some marine creatures such as the Emperor Penguin have developed clever ways to take advantage of this phenomenon. The penguins store air in their feathers, and release them as clouds of bubbles as they swim, making the water around them less dense. By extension, this makes their travel much faster, up to 50% faster. Over the last decade, air lubrication systems have been developed in the marine industry which uses a similar idea - air is pumped beneath the hull of ships to reduce the resistance of water and thereby, fuel consumption.
Another interesting application of underwater bubbles is as a highly effective micro-scrubber. Scientists realized that if ultrasound waves were infused with microscopic bubbles in ordinary water, the normally smooth surfaces of the bubbles start to ripple in response to the high-frequency waves. The thousands of ripples on the surface of the bubble make it rough, which allows it to scrub away at the surface that’s being cleaned.
It’s intriguing to see how physics has packed a punch in something as ‘ordinary’ as a bubble. As Victorian physicist Lord Kelvin rightly said, “Blow a soap bubble and observe it. You may observe it all your life and learn one lesson after another in physics from it”.
About the Author: Navya Nair
Navya is a rising junior in high school from Trivandrum, India. She enjoys learning new things and problem-solving. She is passionate about all the sciences, but am particularly interested in physics.
Furnace. (2013). The Science of Bubbles. curiositystream.com. United Kingdom . https://curiositystream.com/video/3067.
Wikimedia Foundation. (2021, July 6). Surface tension. Wikipedia. https://en.wikipedia.org/wiki/Surface_tension.
Putic, G. (2015). Tiny Bubbles Turn Water Into Effective Cleaning Tool. Voice of America. https://www.voanews.com/silicon-valley-technology/tiny-bubbles-turn-water-effective-cleaning-tool.