Why is the Temperature of Water Low Than Atmosphere?

[anuragkanase]

Hello guys,
This has been my observation and a general physical significance of water, maybe.
I would like to know, why does the water keep its temperature low from the atmospheric temperature?
For example, the room temperature is 29°C and the water kept in steel bucket may measure somewhat lower, 26°C (Say).
So what are the factors responsible for it?
Thank You.

 

[haruspex]

At the surface of the water, the more energetic molecules are escaping (evaporating).
If the relative humidity is less than 100%, more are evaporating than are recondensing from the atmosphere. But that is taking heat energy from the water, so the temperature drops.
Equilibrium is restored when the partial pressure of water vapour in the air equals the saturation vapour pressure of water at the temperature of the water.

 

[anuragkanase]

Thanks a lot. Got it, so the heated water will be evaporated. And the cooler will be remain at bottom. This cycle will be continued... Thanks again.

 

[russ_watters]

That's not what was said. It isn't a matter of selection of the warmer molecules, it is a matter of energy transfer. Selection may play a role in which molecules evaporate, but the temperature drops because of the heat of vaporization.

 

[anuragkanase]

Thanks got the point.

 

[Naty1]

This is evaporative cooling:

Evaporative cooling is a physical phenomenon in which evaporation of a liquid, typically into surrounding air, cools an object or a liquid in contact with it. Latent heat, the amount of heat that is needed to evaporate the liquid, is drawn from the air. When considering water evaporating into air, the wet-bulb temperature, as compared to the air's dry-bulb temperature, is a measure of the potential for evaporative cooling. The greater the difference between the two temperatures, the greater the evaporative cooling effect. When the temperatures are the same, no net evaporation of water in air occurs, thus there is no cooling effect.

http://en.wikipedia.org/wiki/Evaporative_cooling#Physical_principles

Wet bulb temperature is the lowest temperature that can be reached by the evaporation of water only.

http://en.wikipedia.org/wiki/Wet-bulb_temperature

 

[K^2]

It isn't a matter of selection of the warmer molecules, it is a matter of energy transfer.

It's both, actually. Energy barrier acts as both the selector for faster molecules, and to reduce the overall thermal energy. Without both of these mechanisms in place, the equilibrium state would be for both water and air to reach the same temperature.