Why are bubbles round?
Quick Answer
Surface tension pulls the soap film as tight as possible. A sphere holds a given amount of air with the smallest possible surface, so bubbles become round.
The Full Story
A soap bubble is a thin film of water sandwiched between two layers of soap molecules. Surface tension constantly pulls the film inward, trying to shrink its area. For any fixed volume of trapped air, a sphere has the least surface area of any shape, so that is the shape the bubble settles into once it floats free. The shimmering colours come from light reflecting off the inner and outer surfaces of the film, which is only a few hundred nanometres thick. As water drains and evaporates the film thins, and the bubble pops, usually within seconds to minutes.
Key Facts
YouTube Angle
Suggested video title for this topic:
"The Perfect Shape — Why Every Bubble Is a Sphere"