Water sticking to itself isn't water sticking to a surface
- The idea
- Predict
- See it
- Why
- Check
The idea
“Water climbs a narrow tube because it sticks to itself. The tube is just a container.”
Both come from water being polar, and both happen when water climbs a tube. So it's easy to credit the one you remember.
The short version
The mistake: Water climbs a narrow tube because it sticks to itself. The tube is just a container.
What's actually true: Cohesion is water attracted to water. Adhesion is water attracted to something else, so a new surface changes only adhesion.
- Cohesion is water sticking to water. Hydrogen bonds link one molecule's slightly negative oxygen to a neighbor's slightly positive hydrogen.
- Adhesion is water sticking to something else. Polar or charged surfaces like glass, cellulose and clay attract water. Nonpolar wax barely does.
- In capillary action, adhesion pulls water up the walls of a narrow space and cohesion drags the rest along.
On the exam: Water to water is cohesion. Water to anything else is adhesion. If only the surface changed, think adhesion.