Why are small water drops round?
Surface tension favors a smaller liquid surface. For a given volume, a sphere has the least surface area, though gravity and contact with other materials can change the shape.
- The scientific idea
- Surface tension
- Fields of science
- Physics, Chemistry
How it works
A small water drop tends to round up because a sphere encloses a given volume with the least surface area. Gravity and contact with another material can distort the shape, so a large puddle does not become a ball. Surface tension competes with other forces; it does not switch them off.
Look closer
A steel needle carefully supported at the water's surface can stay there despite steel being denser than water. The curved surface helps support its weight. Describing the water as having a skin is a useful comparison, provided we do not imagine a separate solid film. It is still liquid. Soap changes this behavior by lowering surface tension, linking the shape of a droplet to the chemistry of washing.