# Why do clothes dry at room temperature? [duplicate]

When I leave wet clothes in the open air, they will get dry over time by themselves even at room temperature. I know that somehow the water becomes vaporized; it's not "disappearing". For that, it needs to get energy from its environment and probably it's getting this energy from heat. But since it is at the same temperature with the clothes or its environment, I don't understand how an energy transfer can occur. Doesn't this violate the definition of temperature, which is only defined to determine where heat will flow?

So the question can also be expressed as: How can water get heat (if not heat, what?) from its environment when there is no temperature difference so that it can evaporate?

## marked as duplicate by ACuriousMind♦, Daniel Griscom, user36790, Gert, AliJan 12 '16 at 7:25

• The temperature of the cloth is lowered. That is the basis for evaporative cooling. – Lewis Miller Jan 11 '16 at 19:31
• Yes it has to be lowered since it gives heat to water. But what drives this heat transfer in the first place, that is my question. Why should it give heat to water when they had the same initial temperature? – ozgeneral Jan 11 '16 at 19:33
• The heat transfer is driven by the temperature difference. When the water evaporates the temperature of the cloth sinks and this temperature difference drives the heat transfer. The temperature difference will settle into an equilibrium with the heat transfer until all the water that can evaporate is gone. The cloth will, of course, not be completely dry since the atmosphere is not completely dry, either. – CuriousOne Jan 11 '16 at 19:36
• I don't think this is a duplicate because this question is principally interested in how heat can low from cold(er) air to warm(er) water, which isn't addressed by the proposed duplicate. – John Rennie Jan 12 '16 at 7:25

Increasing entropy and decreasing energy are separate goals. In this case, the energy and entropy effects oppose each other, but entropy wins; in general, you can tell which one wins by looking at the change in Helmholtz free energy, $F = U - TS$.