Why Are Bubbles Spherical?

Take a piece of wire and bend it into a square. Dip it in bubble mixture and blow. Why isn’t it a cube-shaped bubble that comes out the other side? Or if the wire is triangular, why can’t you blow a pyramid-shaped bubble? Why is it that, regardless of the shape of the frame, the bubble comes out as a perfect spherical ball?

The answer is that nature is lazy, and the sphere is nature’s easiest shape. The bubble tries to find the shape that uses the least amount of energy, and that energy is proportional to the surface area. The bubble contains a fixed volume of air, and that volume does not change if the shape changes. The sphere is the shape that has the smallest surface area which can contain that fixed amount of air. That makes it the shape that uses the least amount of energy.

Manufacturers have long been keen to copy nature’s ability to make perfect spheres. If you’re making ball bearings or shot for guns, getting perfect spheres could be a matter of life and death, since a slight imperfection could lead to a gun backfiring or a machine gun breaking down. 

The breakthrough came in 1783 when a Bristole-born plumber, William Watts, realized that he could exploit nature’s predilection for spheres.

When molten iron is dropped from the top of a tall tower, like the bubble the liquid droplets form into perfect spheres during their descent. Watts wondered whether, if you stuck a vat of water at the bottom of the tower, you could freeze the spherical shapes as the droplets of iron hit the water.

He decided to try his idea out in his own house in Bristol. The trouble was that he needed the drop to be further than three floors to give the falling molten lead time to form into spherical droplets.

Watts’ clever use of Nature to make spherical ball bearings

So Watts added another three storeys on top of his house and cut holes in all the floors to allow lead to fall through the building. The neighbours were a bit shocked by the sudden appearance of this tower on the top of his home, despite his attempts to give it a Gothic twist with the addition of some castle-like trim around the top. But so successful were Watts’ experiments that similar towers soon shot up across England and America. His own shot tower stayed operational till 1968. 

Neither do I want to have an abrupt wrap-up, nor do I have more words on the fancies of nature. Excerpt from The Number Mysteries by Marcus du Sautoy

~Shamoil Khomosi

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8 thoughts on “Why Are Bubbles Spherical?

  1. I always enjoy how you tend to take a question many wouldn’t bother to ask–“why are bubbles spherical?” give a scientific explanation to the question and then an example of why we should care. Another great post, thank you.

    Liked by 1 person

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