In: Chemistry
Suppose you take a shower on a cold day. Describe the sign of the heat that leaves your body as you step out of a warm shower. Next describe the temperature difference inside and out of the shower. Describe how this example relates to the concept of heat.
There are different ways heat can be transferred - conduction, convection, thermal radiation, and phase changing. Conduction heat transfer comes from coming into physical contact with a substance: here, that substance is water. Convection occurs when air blowing across the body results in heat transfer. One example of thermal radiation is the heat we feel from the sun. And phase change we experience in this situation is the evaporation of water, which takes heat away from the body.
Water conducts heat really well, which is why 70 degree water seems a lot colder than 70 degree weather. Now you're probably thinking that this would make hot showers seem even more unbearable than hot days. Here's why it isn't.
When you're in the shower, not only are you feeling the heat
transferred to your body from the warm water, but that warm water
is also evaporating, and taking heat away from your body, and
simultaneously cooling you. So you are getting heat transferred to
your body through conduction by the water, and transferred away
from your body when it evaporates. So you are being simultaneously
cooled and warmed while in the shower.
On a hot summer day, these things are going on, but at a much
slower rate. Heat is being transferred to our body at a pretty high
rate via radiation from the sun (and other warm objects surrounding
us) while our body is also generating heat. The only way to cool
down is through evaporative heat exchange, and convection. We sweat
which draws heat away from the body through evaporation. Well when
you are sweating, the liquid on your skin will cool you down faster
if you add convection into the mix by standing in front of a fan,
or catching a breeze. But usually on a hot summer day you will not
catch many breezes, and you end up getting more heat transferred to
your body by the sun (on top of the heat your body is already
generating) than you are losing via evaporative heat loss or
convection. Where as in the shower, you are losing and gaining heat
via conduction and evaporative heat loss at a fast rate. If you
were to add a source of heat radiation to the mix, then your shower
would get uncomfortable.