Sweat Is Cool

Sweat…it may be gross, but it is good for you! Sweat is critical to keeping our bodies cool when we exercise or spend any time in the heat. Without sweat, we would quickly get heat exhaustion, or even heat stroke -- a life-threatening condition. In the following activities, students use infrared thermometers to investigate the cooling effects of evaporating water, and see how important hydration is to keeping our bodies cool.

Sweat is Cool was developed as part of the Science of Sweat Workshop, including investigations of how sweat, and more generally evaporating water, can cool things down, and the impacts that extreme heat can have on our bodies. Designed for out-of-school-time educators, the workshop is easily adaptable to other educational settings. Topics include evaporative cooling, the water cycle (including the role of energy), urban heat islands, and staying cool while outdoors. These topics are relevant to spending time outdoors in the heat, they introduce environmental justice and equity issues, and they provide a hands-on introduction to widely taught science concepts.

• Spray bottle of water
• Paper Towels cut/torn into strips approximately 6” x 3”, one per student
• Pipette or small spoon
• Water container
• 2 shallow plates or shallow dishes (at least 6” diameter)
• 2 squares of construction paper that will fit in the dishes
• IR Thermometer(s) (student bulb thermometers can be used if necessary)

Note: IR (infrared) thermometers -- sometimes listed as non-contact thermometers, or “temperature guns” -- allow students to digitally measure the temperature of objects without touching the object. They are wonderful tools for science investigations and can be purchased for $10-$12 and up. Having several will allow students to work in small groups. Choose an IR thermometer that is designed for uses other than (or in addition to) checking body temperature. For example, choose an IR thermometer that is listed as useful for cooking, refrigeration, or swimming pools. Many models have a built-in laser pointer -- this is helpful for aiming the thermometer, and most models allow you to turn this feature off. You can find models without the laser feature if you are not confident that your students can use a laser pointer safely.

Let students familiarize themselves with the use of the thermometers. IR thermometers work by measuring the infrared (heat) emitted by an object. Go over the use of the thermometers, and make sure you decide on using Fahrenheit or Celsius for your measurements (and show students how to change which units the thermometer is using, in case this setting gets changed).

The IR thermometers are fun tools, and it is worth spending some time having students take the temperature of objects around them. Compare temperatures of different objects and surfaces, sun and shade, even different sides of the same object. You can bring an ice pack and/or a cup of coffee to increase the range of temperatures to measure. What are the warmest and coldest things students can find? Looking at the world through a "temperature lens" can become an investigation in itself.

Be Safe: Many IR thermometers have a built-in laser pointer to help you aim the thermometer. Never point the laser into your eye, or into the eye of another person or animal.

Students will naturally want to measure their own, and each other's, temperature. This is fine, but remind them about laser pointer safety. While typical internal body temperature is usually about 97 to 100 degrees Fahrenheit (or approximately 36.5 to 37.5 Celsius) depending on the person, skin temperature can vary even more depending on factors such as sweating, direct sunlight, or which part of the body you are measuring. What happens if students do jumping jacks or other exercises, then measure their temperature?

Keeping our internal body temperature (core temperature) from going too high is important -- we all know how badly we feel when we have a fever! Sweating is key to lowering our body temperature. Sweat is mostly water -- and when it evaporates from our skin it takes heat with it, cooling us off.

How does sweat cool you? Try this -- you might call it extreme sweating:

Give each student a strip of paper towel, about 3” x 6”. Have them hold it over their forearm, then wet it by spraying the paper towel with a spray bottle of water. You should make it wet enough to stick to their arm.

Have students describe what they feel. Using the IR Thermometers, have them compare the temperature of the wet paper towel with a dry section of their arm. How about the skin under the towel?

This activity is most dramatic outside on a sunny, breezy day, but you can also do it inside. If there is no wind, compare how the wet bands feel without wind, and when you fan them or move your arm around to create a breeze.

The water on the paper towel works like sweat. When your body gets too hot, it releases sweat from sweat glands. Sweat is mostly water. The water picks up heat from your body and evaporates -- the liquid water undergoes a phase change to become a gas (water vapor). In this process, the water carries heat away from your body. (In the Water Cycle Simulation [link], the connection between evaporation and energy is explained in more detail.)

Any water will cool you as it evaporates -- it does not have to be sweat. Spraying yourself, or your clothing, with water is a great way to stay cool on a hot day.

What happens to your body if you don’t have enough water to sweat? This simulation can help students picture why it is so important to stay hydrated when out in the heat -- especially when playing sports or exercising. The simulation uses two squares of construction paper to simulate skin, and students monitor their temperature over time.

The activity is best done on a warm, sunny day (see the indoor version if the weather does not cooperate).

To set up, put two plates or shallow containers side by side in the sun. Cut two rectangles of dark-colored construction paper of the same size and color, and the right size to fit on the plates. Spray water over the rectangles to fully wet them, let them drip excess water off, then put one on each plate.

Decide which dish will be the “heat stroke” dish. The other dish will be the “well hydrated” dish. them both.

Observe the dishes every few minutes and use the IR thermometer to monitor the temperature of each dish. Record or graph the temperature over time. (If you have access to computer-based probe software, you can set this up to graph the temperature automatically.)

Keep checking the temperature every few minutes. Whenever the paper in the well-hydrated dish starts to dry out, give it another teaspoon or so of water to “drink”. Keep it well hydrated. However, do not give the heatstroke dish any more water!

What happens to the temperature when the paper in the Heatstroke dish starts to dry out? Continue monitoring until the heatstroke dish is completely dry -- this may be as fast as 10 minutes on a very sunny day.

Homeostasis is a fancy name for keeping something constant. Your body has systems to keep many internal conditions as constant as possible, including the levels of oxygen and sugar in your blood, and your body temperature.

Your body tries to keep your internal temperature near-constant (the "normal" point is usually between 97 to 100 degrees Fahrenheit, or approximately 36.5 to 37.5 Celsius, depending on the person). If your body temperature goes too low (below 95 degrees) your brain and body start malfunctioning and you can even die (hypothermia). If your body temperature goes a few degrees higher than normal, you get heat exhaustion, and if it keeps going higher (104+ degrees) your brain and body start to malfunction -- a condition called heat stroke. Heatstroke is dangerous and requires immediate medical attention.

Optional: You can make the simulation a bit more realistic by first putting two rectangles of paper towel (about an inch larger than the construction paper) on the plate. Spray enough water on each paper towel to fully wet it. Then press construction paper rectangles on top of the wet paper towel. The plate, paper towel, and construction paper should all stick together. The paper towel simulates the interior layers of our body below our skin. This adds a layer of realism, but the simulation will take considerably longer since the paper towel will help keep the construction paper hydrated.

Indoor version: If you need to, you can do this simulation inside, setting up a hairdryer or a fan to blow over the two dishes. However, the temperature rise will not be as dramatic as in the sun.

Using what they know about evaporative cooling, plants, sun and shade, can students invent ways of keeping themselves cool outside? Are there shade structures, or cooling stations they can invent and build? Where should structures be located and oriented to be most effective? Does the time of day matter?

What other ideas can they come up with for investigating temperature, and staying cool? Share your ideas in the I Made It! section below.

PBS video on sweat and cooling:

Summer Science!

Video on recognizing and preventing heat exhaustion and heatstroke:

How to Identify and Treat Heat Stroke | Earth Lab - YouTube

This work is made possible by support from STAR, a Biogen Foundation Initiative. The team at Lesley supporting this initiative includes faculty and staff in the Lesley STEAM Learning Lab, Science in Education, the Center for Mathematics Achievement, and other related Lesley University departments and programs.