Farmer Boy, Chapter 4

Science
Sweat 
Sweat trickled down Mr. Corse’s cheek. Sweat is a body’s natural response to its internal temperature rising. Skin has a very important job, that of protecting our insides from bacteria, dirt, the sun’s rays, and making sure we are kept at a comfortable temperature. The two ways our skin does this is through radiation and evaporation. When our internal temperature rises, a signal is sent from the brain for blood to increase circulation to the skin. This causes the body’s internal heat to be carried by the blood to the skin surface, where it is lost by radiation. As this is happening, our sweat glands, which are little sacs deep in the dermis, start doing their job, releasing perspiration through the pores. This liquid evaporates from our skin, cooling us off. As our internal body temperature drops, our brain then signals to circulate less blood to the skin, and the sweating stops. When the air is humid, meaning it is holding more moisture, the sweat on our skin does not evaporate as quickly, causing us to be sticky and warm.

Do this experiment to see how the rate of evaporation has a direct effect on your temperature:

Dip one cotton ball in rubbing alcohol, and another cotton ball in water. Dab one cotton ball on each of your wrists. Which one feels cooler? Because alcohol evaporates faster than water, the wrist dabbed with alcohol feels cooler. In the same way, the faster our sweat evaporates from our skin, the cooler we feel.

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