Homework answers / question archive / Our body's primary defense against high temperatures is through sweating (perspiration)

Our body's primary defense against high temperatures is through sweating (perspiration)

Earth Science

Share With

Our body's primary defense against high temperatures is through sweating (perspiration). Consider a 185 lb (84 kg) male farmer in the Central Valley of California on a July day when the air temperature is 110°F (43°C). On this day, the humidity is low enough such that all the sweat evaporates from the farmer's skin, enabling him to maintain a body temperature of 100°F (38°C). The farmer sweats 1 liter (1000 g of water) per hour and 60% of the latent heat needed to evaporate this sweat is provided by farmer's body (the other 40% is provided by the air). If the farmer suddenly dehydrates and stops sweating, how long will it take for his body temperature to rise to a near-fatal 110°F (43°C)? Please show all of your work.


Assumptions:
1.     It takes 4200 Joules of energy to warm each kilogram (kg) of his body 1°C (1.8°F).
2.     The latent heat of vaporization is 2,400,000 J/kg. This value means that it takes 2,400,000 Joules of energy to convert one kilogram of sweat (a liquid) into a gas.


Hint: First calculate how much energy it takes to raise his body from 38°C to 43°C. Then calculate how much energy his body was giving away when he was sweating at a rate of 1-liter/hr (1 kg/hr). Use the ratio of these two numbers to find the time!