Why do you cool down more slowly on a humid day than when air is dry?

Answer 1

The answer to this is related to partial pressure of water. When humidity is high this means that there is a lot of water suspended in the atmosphere. This means that water in liquid form will not tend toward evaporation into it's gas phase but will stay as liquid. For more information on partial pressures see: http://en.wikipedia.org/wiki/Partial_pressure

Answer 2

This effect is caused by the partial pressure of the water vapour in the air. The more humid the air, the more water vapour it contains and thus it has a higher partial pressure. This pressure tends to prevent water from evaporating. When the air is completely dry, there is no partial pressure from any water vapour and water will evaporate more quickly. The partial pressure of the water vapour plus the partial pressures of the other gases in the air all add up to create the total pressure of the air. It follows that water will evaporate more slowly when the total air pressure is high and evaporate more quickly when the total air pressure is low.

Answer 3

To cool down, people need to sweat, as when it evaporates it cools the body down. On dry days, it is easy to evaporate, as there is little water vapour in the air. On a humid day, it is harder for the water to evaporate as there is already too much water vapour there. As less sweat evaporates, it takes longer for you to cool down.

Answer 4

Evaporation is based on heat causing water to expand and condense within the dry air. However, on humid days, the moisture in the atmosphere increases, thus reducing the rate of evaporating as the air has already been saturated.

Answer 5

because it is continually secreted from the pores to keep the body temp down so you don't overheat and faint from heat exhaustion

Answer 6

The partial pressure of vapors in the first situation is lower.

Answer 7

Because coldness is less as well.