**Document ID**: 12_14_98_2

**Date Received**: 1998-12-14 **Date Revised**: 1999-01-26 **Date
Accepted**: 1999-02-08

**Curriculum Topic Benchmarks**: S7.3.1, S11.2.4, S7.2.1, S7.2.2, S7.2.4

**Grade Level**: \[3-5\] Upper Elementary

**Subject Keywords**: biology, human body, evaporation, heat loss, heat
transfer, cold weather, wool, cotton, wind chill, hypothermia

**Rating**: Moderate

**Preventing Hypothermia**

**By**: Lorraine Remer Code 913, NASA/Goddard Space Flight Center,
Greenbelt MD 20771 e-mail: remer@climate.gsfc.nasa.gov

**From**: The PUMAS Collection http://pumas.jpl.nasa.gov

©1998, California Institute of Technology. ALL RIGHTS RESERVED. Based on
U.S. Gov\'t sponsored research.

**Concepts:** Hypothermia occurs when a warm-blooded animal, such as a
person, becomes extremely cold, and loses control of his or her body\'s
core temperature. This is much more likely to happen when a person wet
than dry. Hypothermia can cause death. Oftentimes it is difficult to
know when someone starts to go into hypothermia. It is even difficult to
know when you yourself are experiencing the beginning signs.

**Background:** I am very sensitive to the dangers of hypothermia from a
real life experience involving my best friend in high school who almost
died on a back packing trip in the Sierra Nevada mountains. It wasn\'t
very cold, about 40˚F, but it was raining. Her clothing was completely
soaked. She was tired and hungry from physical exertion. She went
through an episode of shivering, then the shivering stopped and she
thought she was fine. That\'s when she slipped into unconsciousness. Her
hiking partners acted quickly. They stopped immediately, set up a tent
and warmed her up with their own body heat. She was lucky.

**Materials:** Desk fan. Thermometer with exposed bulb. Cotton or gauze.
Bowl of water. Socks or fabric consisting of a variety of materials
including cotton and wool. Perhaps a magnifying glass. Big paper doll
with a wardrobe of paper clothing both appropriate and inappropriate for
cold weather activity.

**Prelude:** As an introduction to these activities I sometimes read
from Laura Ingalls Wilder\'s *The Long Winter*. See a related PUMAS
example: Hypothermia in the Little House.

**Activity #1**: Cooling by evaporation. Hold up the thermometer. Have
volunteers come up to read the temperature. Get several readings. Next,
turn on your desk fan. Hold the thermometer in the "wind" produced from
the desk fan. Have several volunteers read the temperature. The
temperatures should be the same as before. Then, dip the cotton gauze in
the bowl of water. Hold the wet gauze on the thermometer bulb and hold
the thermometer in the \"wind\" from the fan. This time when the kids
come up to read the temperatures they will find that the temperatures
are dropping.

What is happening? The water next to the thermometer bulb is
evaporating, and evaporation causes cooling. The reason that evaporation
cools is that the gas state of water molecules is more active and at a
higher energy level than the more organized liquid state. It takes
energy to get those molecules up and moving. The energy that goes into
the water to make gas from liquid has to come from the environment
surrounding the water. The environment loses energy and cools when the
water gains energy and turns from liquid to gas. The moving air
accelerates the evaporation allowing liquid to turn into gas more
quickly.

Why didn\'t the wind cause a cooling? What about wind chill? Wind chill
only affects warm bodies that manufacture their own heat. A warm body
conducts heat into the air layer that directly touches the body. That
warm layer of air, in part, insulates the body from the colder air
beyond. If a wind comes along and moves those warmer air molecules away
and replaces the warmer air molecules with colder molecules, the warm
body has to go to work again to warm up the insulating air layer. The
reason it feels colder to you with a wind than without is because your
body has to work harder repeatedly heating up the air molecules that are
in direct contact with your body. The thermometer doesn\'t manufacture
its own heat therefore it is the same temperature as the air in the room
and doesn\'t lose heat in warming up the air around itself.

Moral of this lesson: Don\'t get wet when its cold!

**Activity #2**: Have the kids dip different fabrics in the bowl of
water. I use socks. Note carefully which socks get soaking wet
immediately and which stay dry on the inside. Note when you see air
bubbles. Cotton absorbs water right away. Wool produces a lot of air
bubbles and stays dry for a long time. Examine wool fiber closely, maybe
with a magnifying lens. Wool fibers are squiggly.

Clothing keeps you warm because 1) it keeps you dry and 2) it traps an
insulating layer of air around your body. The squiggly wool fibers trap
a lot of air. Even when you dunk wool in water, it doesn\'t lose all the
air trapped in the fibers. Wool will keep you warm a long time. Cotton
will not. Your denim blue jeans are made from cotton, and will get wet
right away. They\'ll cause evaporation against your skin right away and
will make your body work hard at keeping warm.

Moral of this lesson: Don\'t wear cotton. Wear wool. (Man-made fibers
vary. Some are like wool and some like cotton.)

**Activity #3:** Choosing clothing. I made two paper dolls, one a boy,
one a girl. They are about 12 inches high and come with a variety of
color-coordinated clothing. It took me about 90 minutes to make each
doll with its wardrobe. Each doll has thermal underwear, denim pants,
wool pants, wool socks and cotton socks, canvas tennis shoes, boots,
mittens, wool sweater, short sleeve T-shirt, long sleeve cotton shirt,
hooded cotton sweatshirt, rain pants and a rain poncho, ear muffs, a
wool ski cap and a baseball hat.

The kids and I spend some time dressing him or her for winter activity.
I might say, "It's cold and rainy." Then I would expect the clothing
choices to include boots, rain pants and the poncho. I might say, "It's
snowing." Then the poncho is less important and the wool sweater is more
important. The ski cap is essential and the baseball hat and the ear
muffs are useless. (You lose most of your body heat through your head
and neck.) I emphasize layering, protection from wet, and a head
covering. Canvas tennis shoes are bad. Wool is better than cotton. Make
sure your thermal underwear isn\'t all cotton. The idea is to let the
kids make the choices, and to guide them into making the right choices.
Its a nice application of science into everyday life.