Foam Is Mostly Air Held in Place by Liquid
Foam is a mass of small bubbles. Its structure follows a geometric rule discovered in the nineteenth century.
Foam is a mass of small bubbles formed on or in a liquid. Its architecture is not random. The Belgian physicist Joseph Plateau showed that in any stable foam, three films always meet along an edge at exactly 120 degrees, and four edges meet at a point at about 109 degrees. Every soap foam obeys these rules because any other arrangement has more surface area and collapses. *Foam* is Old English, related to Latin *spuma*, which gives *pumice*.
- A mass of bubbles. *Sea foam.*
- To produce foam. *The beer foamed.*
- A light solid. *Foam rubber.*
- Froth — a near synonym. *Froth.*
- Old English — *fam*. *The source.*
Word forms
| Form | Word | Example |
|---|---|---|
| Noun | foam | Foam. |
| Verb | foam | Foaming. |
| Adjective | foamy | Foamy. |
| Related | froth | Froth. |
| Latin | spuma | Foam. |
- Foam gathered along the shore.Sea.
- The cushion is foam rubber.Material.
- Three films meet at 120 degrees.Physics.
Plateau's rules for foam
- Films are smooth and meet in threes along an edge
- Those three films meet at exactly 120 degrees
- Four edges meet at a vertex at about 109 degrees
- Any other arrangement has more surface area and is unstable
- Named after Joseph Plateau, who set them out in 1873
Old English *fam*, of Germanic origin, related to Latin *spuma*, foam.
Why do foam bubbles meet at 120 degrees?
Because any other angle gives a larger surface area, and surface tension pulls films into the arrangement with the least area.
Who was Plateau?
Joseph Plateau, a Belgian physicist who set out the geometric rules that all stable foams follow, published in 1873.