10.3 Space Figures

Question

Natalie asked her teacher why, when you blow bubbles, they are round like a sphere and not cubes or other shapes. Research the question and then write a response you can give to this student.

Answer 1

Hi Karen P.,

Didn't I just answer another question from you???

Anyway, the shape a bubble surface takes is governed by its edges (more on this in a moment) and by energy concepts. If you have a free-floating, small bubble (no edges) it will be very close to spherical. That is b/c the surface is being pulled together by the force called "surface tension", so it tries to be as small as possible while still holding the contents in. That shape is a sphere -- it has the smallest surface area : volume ratio of any 3-D shape. There may be a trifle of distortion from uneven distribution of the liquid -- it tends to drain to the bottom, which you can see in bright light from the play of interference colors on its surface. And, also, for very large bubbles (think, the magicians at carnivals and fairs!), the shape of the bubble is blown about by the local breeze and by the turbulence of creation, and it may lazily change shapes as it drifts, and coats your younger brother with slimy goop.

Now, if your bubble is supported on a frame, then things can get interesting! But under all conditions, the bubble shape will be that so as to minimize the total surface area of all the combined surfaces.

You might want to arrange some experiments! If you had a viscous liquid and blew bubbles into the bottom of it, would the bubbles necessarily be spherical as they rose? You might want to briefly watch a "lava lamp" video (such as https://www.youtube.com/watch?v=h_lQ2tMgLVM ) and verbally explain what's taking place!

Good luck with your research,

-- Mr. d.