Make a Thermometer to Study the Temperature

Background Information for Teachers

This section contains a quick review for teachers of the science and concepts covered in this lesson.

Temperature, a measure of warmth or coldness, is an important part of a weather report because we want to know how warm or cold it will be the next day or the following week. Scientists use the outdoor air temperature as one of many variables to specify weather. Monitoring temperature over a longer period of time and at different locations allows scientists to identify temperature changes and patterns. These patterns can then be used to predict future weather.

A device that measures temperature is called a thermometer. One type of thermometer is the liquid-filled thermometer. It consists of a liquid-filled reservoir at the end of a narrow tube. If the temperature of the liquid in the reservoir increases, it expands and rises into the narrow tube. When the liquid cools, it contracts, allowing the liquid in the tube to fall to a lower level. Therefore, high levels of liquid in the tube indicate a higher temperature, and low levels indicate a lower temperature. Figure 1 shows an example.

To compare temperature readings from different thermometers, a thermometer has to be calibrated. When calibrating a thermometer, a number value is assigned to a certain level of liquid in the narrow tube, and thus matched to a specific temperature (hotness or coolness). There are several different measurement units for temperature. Celsius and Fahrenheit are two commonly used temperatures scales. Both scales use the temperature at which water freezes and boils at sea level as reference points. The scale is then created by breaking the section in between these reference points down into equidistant intervals. As shown in Table 1, temperature scales can differ in the numbers chosen to represent these reference point temperatures.

When it gets cold enough, the temperature readings can become negative for the Celsius scale, the Fahrenheit scale, and the scale used in the thermometer created in this lesson. Because thermometer readings change in discrete steps (for example, consecutive readings could indicate 2°C and 3°C, or 10°C and 25°C), students might get the impression that the temperature changes stepwise, in jumps. This can reinforce a common misconception that "cold" and "warm" are two different entities rather than extremes of a continuum. Arranging pictures on a continuum from very cold to hot might help to clear up this misconception.

In this lesson plan, students will build their own liquid thermometer and use it to monitor temperature changes over time and at different locations. They can then look for patterns in their measurements to understand more about their local weather.

Additional Background Links

• Weather Fundamentals, Weather Almanac
• Temperature, Ducksters Education Site
• Temperature, Weather Wiz Kids

Prep Work (5 minutes)

• Measure or look up the local outdoor temperature at the time of the students' last break before this lesson is taught.
• Optional: Build a thermometer yourself to gain familiarity with the steps.

Engage (20 minutes)

Explore (60 minutes)

Making the thermometer

Tell the students they will make their own liquid thermometer in small groups.

Form groups of 2 or 3 students, provide the materials, and guide the class through the process. You can also use this video to show the students how to make the thermometer. Remember to work in a well-ventilated room, and to close the bottle of rubbing alcohol when not in use.

Note: the thermometers work well over a time span of a few days but need to be recalibrated when used over longer periods of time. This happens because the alcohol evaporates.

1. Liquid-filled thermometers consist of a liquid-filled reservoir at the end of a narrow tube. The clear drinking straw will become the narrow tube of your thermometer. Use a permanent marker to mark the straw, from the top down, at half-centimeter intervals. These will serve as level marks on your thermometer. Alternating between two colors is not necessary, but can make it easier to read the thermometer.

2. Modeling clay will seal the bottle's neck and hold the straw in place. Mold the clay until it feels soft and elastic, then form a ball and push it flat. This round, flat piece of clay should be bigger than the neck of your bottle. Use your straw to punch a hole in the middle of this round piece of clay, just big enough to allow to straw to go through. Remove any clay clogging the straw.

3. Help students add rubbing alcohol to the bottle, filling it about a third to halfway up. Reseal the bottle of rubbing alcohol immediately to minimize evaporation and exposure to fumes. Add a couple of drops of food coloring to the alcohol, close the bottle, and shake it so the liquids mix well. This will be the liquid-filled reservoir of your thermometer.
4. Open the bottle and fill a medicine dropper or syringe with the colored rubbing alcohol. Carefully set the medicine dropper or syringe aside, preferably on a paper towel or cloth in case any liquid leaks out. If the level of liquid in your bottle dropped below one quarter of the way up, add a little more rubbing alcohol to the bottle so the level is between one quarter and halfway up the bottle.
5. Poke the straw through the hole in your modeling clay and place the clay on the bottle's neck so the straw hangs into the bottle. Adjust the straw so the end is immersed in the liquid, but does not touch the bottom of the bottle. The majority of the straw will be sticking out from the bottle.

   Ask the students why they think the straw should not touch the bottom of your bottle.

6. Use the clay to seal the bottle opening and hold the straw in place. Important: Make sure the clay forms an airtight seal around the straw and over the mouth of the bottle, but do not close off the straw's opening.

   Ask students if they can think of a reason why it is imperative that air cannot enter the bottle.

7. Drip the content of your medicine dropper or syringe—drop by drop—into the straw. Start a discussion with the students. What happens? If liquid rises up the straw and stays there, why does it do that? If liquid drops down into the bottle, why does that happen?
   Image Credit: Sabine De Brabandere, Science Buddies / Science Buddies
   Figure 7. Build a liquid column by dropping colored alcohol into the straw.

   If your seal is airtight, no air can flow out of the bottle to make room for additional liquid, so the liquid drops down the straw and forms a column. If your seal is not airtight, liquid running down the straw flows into the reservoir, pushing air out of the bottle. If this happens, remove the clay and straw and go back to step 4, making sure the clay forms an airtight seal at the bottle's neck and around the straw when executing step 6.

8. The fluid level in the column should reach about midway up the visible part of the straw. If needed, use the dropper or syringe to add more alcohol (uncolored is fine this time) to the straw.
9. Observe the fluid level in the straw. Ask students how they think the fluid level will change if the bottle is cooled or warmed?

   To test, add cold water to a bowl. Place ice cubes in the water so the water cools to 0 degrees Celsius (32 degrees Fahrenheit). Place your thermometer reservoir in the ice cold water and let the thermometer adjust to its new situation.

   Start a discussion with the students. What happens? Is it similar or different from what you expected? Could this measurement help you add a scale to your thermometer?

10. Mark the level of the liquid in the narrow tube indicating 0 degrees Celsius/32 degrees Fahrenheit.

Common mistakes to draw students' attention to:

• Remove the clay plugging the straw after pushing the straw through the flattened ball of clay so liquid can flow in and out of the straw.
• Immerse the end of the straw in the liquid without letting it touch the bottom of the bottle so liquid can flow in and out of the straw.
• Seal the bottle airtight with clay. This ensures that expanding air and liquid in the bottle pushes the liquid up the straw instead of pushing air out of the bottle.

Testing the thermometer

Gather the class for a discussion.

Perform the experiment as a class. If you have three similar thermometers*, place one in each bowl simultaneously. If the thermometers are quite different, choose one and use it to measure the temperature of the water in the bowls sequentially, starting with the ice water bath.

*A similar thermometer is one with the same diameter straw, the same bottle as the reservoir, and similar amounts of liquid in the bottle.

Using the thermometer for temperature measurements

Go back to your groups and use the thermometer you made to measure the temperature of following surroundings:

• Room temperature
• Outside temperature
• The temperature of your hands. This can be measured by curling your hands around the thermometer.
• If you have easy access to a refrigerator, a pool, and/or a freezer, allow the students to measure the temperature of those environments as well.

Ask students to record their measurements in a table. The worksheet provides an empty table for students to fill in. Have them represent the measurements in a bar graph. A graph template is provided in the worksheet.

While the students measure with their homemade thermometers, perform the same measurements with a store-bought thermometer (in degrees Celsius or Fahrenheit). Represent these measurements in a bar graph.

The worksheet answer key provides example measurements obtained with a homemade thermometer and their associated graph. Figure 9 shows the graph together with example measurements obtained from the same locations and time using a store-bought thermometer.

Bring the class together and ask one group to show and explain their graph to the class.

Allow the students to ponder this question in their small groups. Direct them to Question 3 of the worksheet to work on individual answers before continuing as a class.

Note: If students have questions about their own thermometers not being identical, explain that different size of the bottle, diameter of the straw, and amounts of liquid and air in the bottle lead to different readings for the same temperature change. Because they all measured similar temperatures, the trend (e.g. higher, lower, double, etc.) is identical even though the numbers might slightly differ.

Reflect (15 minutes)

If other variables used in specifying the weather will be studied in other lessons, briefly mention them here.

Assess

The answer to Question 4 on the worksheet can be used to assess students understanding.

The quiz and answer sheet are an additional option to assess students.

Lesson Plan Variations

• Students can use their thermometer to record the temperature changes during a day and compare it with their predictions.
• Students can follow the temperature over a larger period of time and see how temperatures change over different time periods like hours, days, and seasons. Unfortunately, their homemade thermometers are not well suited for long-term use, as the alcohol in the straw evaporates.
• Students can look for patterns in temperature data and use it to predict the temperature. Challenge students to find other factors that can make their prediction more accurate, like whether or not it is overcast that day.
• Students can use straws of different diameters to create their thermometer and see how that influences the readings. What is the advantage and disadvantage of a smaller/larger diameter? Which thermometer would work best for their climate?
• Challenge the students to find a place where the current temperature is in a specific range, like -20 to -10, -10 to 0, 0 to 10, 10 to 20, 20 to 30 degrees Celsius.
• Challenge the students to find global patterns in the weather, like the seasonal changes in the northern and southern hemispheres or temperatures close to the equator compared to temperatures at larger latitude.
• Challenge students to find the warmest and coldest place on Earth, and list how cold and warm it gets.