Q: Why are bubbles round?
A "The size and shape of bubbles and balloons are determined by a competition between their surface tension, which makes them contract, and their internal pressure, which makes them expand," said UW-Madison physics professor Clint Sprott, who is founder of "The Wonders of Physics" campus and traveling show.
Surface tension, which causes a bubble to contract, results from water molecules attracting one another. Air pressure, the outward force, is caused by trapped air molecules colliding with the bubble's inner surface.
"Both factors decrease as the bubble gets larger, but the pressure decreases faster, limiting the size of the bubble," Sprott said. "The pressure is smallest when the volume inside is the largest, and a sphere is the shape with the largest volume to surface ratio."
This concept also explains why two soap bubbles in contact combine into a larger bubble. The merger reduces the surface area, which increases the ratio of volume to surface area.
So is it possible to create a cubic bubble? Without outside forces, a spherical bubble will always be favored over a cubic bubble. Nevertheless, it's an experiment for all curious bubbleologists.
— Provided in cooperation with University Communications