Ever hang up clothes to dry indoors and wonder how that occurs? It makes more sense that something wet would dry when laid out in the sun, but it is less obvious why wet clothes dry hanging in my basement.
As we all know, the process of drying is called evaporation. Evaporation is technically defined as the process of a liquid turning into a gas at other than its boiling point. Evaporation occurs because liquid molecules are in constant random motion. In random motion, the molecules are at different speeds and keep changing as the molecules bang into each other. When a molecule near the surface of the liquid gets sufficient speed or energy, it escapes from the liquid surface and becomes vapor, leaving less liquid behind.
Liquid can evaporate at any temperature but occurs faster at higher temperatures. Other factors that effect the rate of evaporation include the temperature of the air, the humidity of the air and the size of the surface exposed, among others.
How is evaporation different from boiling? Boiling occurs when a liquid reaches its boiling temperature – for water its 212 degrees Fahrenheit. Boiling occurs throughout the liquid whereas evaporation is just at the surface of the liquid. Boiling requires an external energy source while evaporation occurs at any temperature. With boiling vaporization occurs quickly and bubbles are formed. Evaporation takes much longer.
You should follow up with a discussion on how evaporation occurs on a garment–from the bottom up as I recall, not from the top down.