Water at work
Follow water as it escapes, condenses, bubbles and climbs.
- How can a wet towel dry at room temperature? Water molecules can escape from a liquid's surface into the air even below boiling temperature. This surface process is evaporation, and it can cool what remains.
- Why does a cold glass get wet on the outside? Water vapor already in the air can turn into liquid on the cold surface. The droplets usually come from the surrounding air, rather than passing through the glass.
- Why doesn't boiling water keep getting hotter? During steady boiling at a fixed pressure, added heat mainly turns liquid water into vapor. The boiling temperature itself depends on pressure, so it is not always 100 °C.
- 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.
- How does a paper towel pull water upward? Water wets the paper's fibers and moves through the narrow spaces between them. Surface tension and interactions with those fibers produce capillary action, which can lift water against gravity.
- Why does water conduct electricity? Ordinary water contains dissolved ions: electrically charged particles that can move through the liquid. Their movement carries electric current. Highly purified water conducts electricity very poorly.