Lab / experiment Grade 2 Health & Consumer Science
Two Thermometers and a Paper Fan: A Grade 2 Sweat Cooling Lab
Grade 2 students fan a dry thermometer and a wet-wrapped one, graph how a damp hand felt, and use the results to explain how sweat cools skin and why we drink after.
Objectives
- Students will record and compare the readings of a dry thermometer and a wet-wrapped thermometer after both are fanned the same way for the same time.
- Students will draw and read a single-unit bar graph of the class hand-test results.
- Students will explain, using their own results, that sweat cools the skin as it dries into the air.
- Students will name drinking water as the way to replace the water the body loses in sweat.
Vocabulary
Key words: sweat, evaporate, thermometer, degrees, fair test
Teacher overview
Sweating is the main way the body cools itself during hard play, and the water that leaves in sweat has to be replaced by drinking. In this lab, a second-grade class at Stonechat School (a fictional school) first feels the difference between a damp hand and a dry hand in moving air, then runs a fair test with two matching thermometers. One thermometer stays dry, the other is wrapped in a wet paper towel, and both are fanned the same way for four minutes. The wet thermometer's reading drops as its water dries into the air, which gives students measured evidence that sweat cools the skin as it evaporates. The water that leaves the paper towel, like the water that leaves sweaty skin, becomes water vapor in the air, the same step of the water cycle that students see when a puddle dries in the sun.
A common misconception at this age is that sweat is only a sign of being dirty or unwell, or that sweat makes a person hotter, and many children have not yet linked sweat with cooling or with the water it takes out of the body. The hand test in Part A cannot settle the question alone, because tap water feels cool on warm skin whether or not it dries. The thermometer test in Part B is the fair comparison: the water sits out ahead of time so it starts at room temperature, both thermometers start at the same reading, and the only difference between them is the wet wrap. When the wet thermometer falls below the dry one, the drying is the cause. Before the lab, ask the class what sweat is for and write their ideas on the board, then return to that list during questions 7 and 8. Teachers may also point out that sweat dries more slowly on a damp, sticky day, so the body cools less well and needs more rest in the shade and more water breaks.
Prepare the cups of water at least an hour ahead, because cold water straight from the tap will make the wet thermometer read low before any drying happens and will spoil the fair test.
Procedure
Work in groups of four. Your teacher will read each step with you.
Part A: The hand test
Step 1. Take one cotton ball. Dip it in the cup of water. Squeeze it so it does not drip.
Step 2. Wipe the wet cotton ball on the back of one hand. Keep your other hand dry. Throw the cotton ball away. Each person uses a new one.
Step 3. Hold both hands out in front of you. A partner fans both hands with the paper plate while you count slowly to 20. Safety note: fan hands only, and keep the plate away from faces and eyes.
Step 4. Which hand felt cooler? Pick one: wet hand, dry hand, or felt the same. Make one tally mark on the class chart.
Step 5. Take turns until each person in your group has had a turn. Dry your hands on a paper towel.
Part B: The thermometer test
Step 6. Lay the two thermometers flat on the desk, side by side. Keep them out of the sun. The bulb is the round end with the red liquid in it. Do not hold the bulb, because a warm hand will change the number. Safety note: if a thermometer breaks, do not touch it. Tell your teacher right away.
Step 7. Wait one minute. Then read both thermometers. Find the top of the red line and read the number next to it. Write both numbers in the "Before fanning" row.
Step 8. Dip one paper towel square in the cup of water. Squeeze out the extra water. Wrap the wet square around the bulb of one thermometer and hold it on with the rubber band. This is the wet thermometer. The other one stays dry. Safety note: wipe up any spilled water so no one slips. Do not drink the water in the cup.
Step 9. Fan both thermometers at the same time and in the same way. Each person fans for one minute, then passes the plate to the next person. The water in the cup has been sitting out, so it is as warm as the room. Both thermometers get the same fanning for the same time, and the only difference is the wet paper towel. That is what makes this a fair test.
Step 10. After 2 minutes of fanning, stop and read both thermometers. Write the numbers in the "After 2 minutes of fanning" row.
Step 11. Fan for 2 more minutes. Read both thermometers again and write the numbers in the "After 4 minutes of fanning" row.
Part C: The class bar graph
Step 12. Count the tally marks for each choice on the class chart and write the totals in Table 1. Then draw a bar graph with one bar for each choice. Each box on the graph stands for one student.
Data & Analysis
Table 1: Class hand test
| Choice | Tally marks | Number of students |
|---|---|---|
| Wet hand felt cooler | ||
| Dry hand felt cooler | ||
| Felt the same |
Table 2: Our thermometer test
| When we read it | Dry thermometer (degrees) | Wet thermometer (degrees) |
|---|---|---|
| Before fanning | ||
| After 2 minutes of fanning | ||
| After 4 minutes of fanning |
Answer each question. Use your tables and your class bar graph.
- Look at your class bar graph. Which choice has the tallest bar: wet hand, dry hand, or felt the same?
- Use your class bar graph. How many more students chose wet hand than dry hand?
- Before fanning, did your two thermometers show the same number? Write yes or no.
- After 4 minutes of fanning, which thermometer showed the lower number: the dry one or the wet one?
- Look at the "After 4 minutes of fanning" row in Table 2. Take the wet number away from the dry number. How many degrees cooler was the wet thermometer?
- Suppose a group's dry thermometer read 73 degrees and its wet thermometer read 66 degrees. How many degrees cooler was the wet thermometer?
- Sweat is water that comes out of your skin. Think about the wet thermometer. What does sweat do for your skin as it dries?
- Sweat takes water out of your body. What should you do after you run hard and sweat at recess?
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Answer Key
- Answer: Wet hand, in most classes.
Accept whichever bar is tallest on the student's own class graph. Most students feel the damp hand grow cooler as the water dries in the moving air. - Answer: Accept the class's wet-hand total minus its dry-hand total.
The number must match the class graph. For example, a class with 16 wet-hand tallies and 3 dry-hand tallies would answer 13 students. If more students chose dry hand, accept an answer that says zero more, or that says how many fewer. - Answer: Yes, in most groups.
Both thermometers were dry and in the same spot, so they should match. Accept a difference of 1 degree, which comes from reading between the lines of the scale. If a group's readings differ by more, check that neither thermometer was held by the bulb or set in sunlight. - Answer: The wet one.
The wet thermometer should read lower at 2 minutes and lower again at 4 minutes. If a group's wet thermometer did not drop, the paper towel may have been too dry, the water too warm, or the fanning too light; let the group repeat Steps 8 to 11. - Answer: Accept the dry reading minus the wet reading from the group's own 4-minute row.
The answer should be a whole number of degrees greater than zero, and it should match the table. A group that recorded the same number for both should be asked to check the paper towel and try again. - Answer: 7 degrees.
73 minus 66 is 7. Check by adding: 66 plus 7 is 73. - Answer: It cools the skin.
Accept any answer that links drying to cooling, such as "Sweat dries into the air and that makes my skin cooler, like the wet thermometer." A strong answer names the evidence: the wet thermometer got cooler as its water dried while the dry one stayed about the same. - Answer: Drink water.
Sweat is water leaving the body, so drinking water puts it back. Accept "get a drink at the fountain" or "drink from my water bottle." Answers that add resting in the shade are also correct.
Differentiation
Support
Put a small piece of tape beside the top of each red line at the "Before fanning" reading so students can see the red line move down from that mark. Read the thermometers with the group and say the numbers aloud together. For question 5, give students a number line from 50 to 80 so they can count back from the dry reading to the wet reading. Accept spoken answers to questions 7 and 8, written down by an adult.
Extension
Set up a third thermometer beside the others, wrapped in a wet paper towel but not fanned. Ask students to predict, then check, whether the wet thermometer in still air cools as much as the wet one in moving air. Have them write two sentences about what the result means for choosing a shady, breezy spot to rest on a hot day, using their readings as evidence.
ELL supports
Pre-teach sweat, wet, dry, cooler, and thermometer with picture cards and gestures, such as wiping a forehead for sweat and waving a plate for moving air. Give sentence frames for questions 7 and 8: "When sweat dries, my skin gets ___." and "After I sweat, I should ___." Allow students to answer questions 3 and 4 by pointing to the correct thermometer or row in the table.
Extensions
After the next recess on a warm day, ask students to notice signs of sweat, such as a damp forehead or a damp shirt collar, and then hold a short class talk. Students use their thermometer results to explain where the water in that sweat is going and why the class stops at the fountain or at water bottles on the way back inside. Each student can then make a small hot-day card for the desk that states two things the class tested and discussed: sweat cools the skin as it dries into the air, and a drink of water puts back the water that sweat carries away.