c. Evaporation in the form of sweating is a way the body can lose heat if the air
temperature is greater than the person's body temperature.
d. Evaporation does not necessarily require sweating because there is a
continuous spreading out of water molecules through the skin. About 20 to 25 percent
of the body's normal heat production is lost by evaporation. Humans can increase this
type of heat loss by sweating; animals increase this type of heat loss by panting and
without physical contact. The human body loses heat by the radiation of heat waves
from the body to cooler objects nearby such as ceilings, floors, and walls. If these
objects are at a higher temperature, a person's body absorbs the heat--also by the
process of radiation. The temperature of the air has no relation to the radiation of heat
to and from objects. That is why skiers can remove their shirts and be warm in bright
sunshine even though the air temperature is low. The radiant heat from the sun warms
Figure 4-2. Radiation--heat from the sun.