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Absolute Zero

Classroom Activity


Activity Summary
Students build and calibrate their own bulb thermometers.

Learning Objectives
Students will be able to:

  • understand how a bulb thermometer works.

  • create a temperature scale for their thermometer.

  • convert between Fahrenheit and Celsius temperature scales.

Materials for Teacher
  • various thermometers and temperature probes for display (do not use mercury thermometers)
  • nail and hammer
  • ballpoint pen or pencil
  • 3 hot plates
  • 3 large containers (for warm water)
  • paper towels
Materials for each team
  • copy of the "Building a Bulb Thermometer" student handout
    (PDF or HTML)
  • copy of the "Calibrating Your Thermometer" student handout
    (PDF or HTML)
  • 170 g (6 oz) baby food jar
  • clear straw
  • room-temperature water
  • 1000 ml beaker
  • water
  • crushed ice
  • plasticene or modeling clay
  • food coloring
  • plastic pipette
  • 8-cm x 13-cm (3-in x 5-in) index card
  • tape
  • ballpoint pen
  • thermometer (to measure water temperature)

While humans have always wondered about cold, the earliest known studies about cold began in the 1600s. One of the first steps toward understanding cold was to determine how to measure it. Grand Duke Ferdinand de Medici invented the first accurate thermometer in 1657. Now thermometers are everywhere.

Three main scales are in use today: Fahrenheit, Celsius, and Kelvin. A pioneer in developing alcohol and mercury thermometers, Daniel Fahrenheit devised a scale in the early 1700s where he marked zero to represent the temperature of equal parts of ice, water, and salt. On this scale, the freezing point of water is 32 degrees, and the boiling point is 212 degrees. In 1742, Anders Celsius developed a scale where he labeled the freezing point of water as 100 degrees and the boiling point of water as 0 degrees, and marked off 100 equal degrees between them. (Today's Celsius scale reverses the 0 and the 100.) The third type of scale is named after Lord Kelvin, who proposed the Kelvin scale in the mid-1800s. The Kelvin scale—which is based on the Celsius scale, but has no negative numbers—is widely used by scientists. The Kelvin scale uses the triple point of water (the temperature at which water exists simultaneously as a solid, liquid, and gas, 273.16 K) and the boiling point of water (373 K) as its fixed points. Zero on the Kelvin scale is considered to be absolute zero, the point at which all molecular motion stops.

In this activity, students build and calibrate a simple bulb thermometer.


Part I

  1. Prepare the container tops for students' bulb thermometers prior to the activity. While the lid is still on the jar, tap the nail into the middle of the jar lid. Using the hammer to tap the top of a ballpoint pen or pencil so that the tip is inserted to the point shown (see illustration). This will open the hole just enough so the straw will go through. While a larger hole can be plugged with clay, there is a much higher chance of the liquid leaking out during the experiment if the hole is even a bit wider than the straw. Remove the jar labels (otherwise they will fall off while in the warm water bath).

    Pencil and pen

    Insert pen or pencil in the jar lid to the point shown to create a hole with the proper diameter.

  2. Ask students to brainstorm all the thermometers that can be found in their homes. (Some examples include thermometers to measure outside temperatures, thermometers to measure body temperatures, and kitchen thermometers used to measure food temperatures in meat and candy.) Ask students to find as many types of thermometers as they can in their homes and record the range of temperatures on each and the temperature that the thermometer reads when found.

  3. Display the thermometers you brought in. Make a list on the board of all the thermometers students found, and show a sample of each if you have one. Have each student report temperature ranges and the temperature reading of the thermometer. Which temperature scale does each use (Fahrenheit or Celsius)? What are the similarities and differences in the temperature ranges on each instrument? How similar were their temperature readings when they were found? What would explain any differences?

  4. Explain to students that all thermometers depend on some material that changes their properties when their temperatures change. A liquid bulb thermometer, such as the classic mercury thermometer, relies on the fact that liquids expand as they get warmer and contract as they get colder. Students will make a homemade liquid bulb thermometer in this activity.

  5. Organize students into teams. Provide each team with the handouts and materials listed. Have students make their thermometers. Before students calibrate their thermometers, check each team's thermometer to make sure that the clay is well sealed around the straw, that the jars are as tightly sealed as possible, and that the water levels are at about halfway up the straw.

Part II

  1. Create three warm water baths at a station in the room for students to use to calibrate their thermometers; the water should reach at least halfway up the jar but not go over the top (remember to take into account how many students may be using the warm water bath at once as this will raise the water level). Use a hot plate to keep the warm water bath between 45 and 50 degrees C. Keep an eye on the warm water bath during the activity to ensure it is maintaining its temperature (using as large a container as possible will help keep the bath a constant temperature).

  2. Have students make their own ice water baths in beakers. Provide paper towels near each bath for cleanup. Students should do the ice water baths first; if they do the warm water bath first, it will take a long time for the liquid in the jars to cool enough to show a noticeable decrease in volume.

  3. After students have used their reference thermometers to calibrate their homemade thermometers, review answers to the questions on the student handout. Explain the three most typical temperature scales used (see Background for more information). What would each of the three different scales be good for measuring? What would their homemade thermometers be good for measuring? (Their thermometers would be best for measuring a very narrow temperature range, such as how the temperature in the classroom changes throughout the year.)

  4. To illustrate how the first universally accepted temperature scales were invented, show students the portion of the program at right that presents how Daniel Fahrenheit and Anders Celsius came up with their scales.

    After students have viewed the video, ask them what the value is in having everyone agree to use a specific scale. (A universally accepted scale means that the thermometer can serve as a common reference point for temperature measurements, thus providing a standard "language" for temperature.)

  5. As an extension, work with the students to research how other types of thermometers—like turkey pop-ups, Galileo thermometers, and digital thermometers—work.

Activity Answer

Water expands as it gets warmer, and contracts as it gets colder. As the water in the jar of the thermometer got warmer, it expanded and had nowhere to go but up through the straw. Then, when the thermometer was used to measure something colder, the water in the jar got colder and contracted and sank down in the straw. This principle of volume change can be used to measure temperature.

While thermometers measure a change in temperature, the numbers used to describe that temperature are arbitrary. The numbers are simply a scale that a set of people agree to use; different scales are useful for different situations. The United States, for example, uses the Fahrenheit scale, while much of the rest of the world uses the Celsius scale.

The following scale was created for a thermometer built using a 170 gram (6-ounce) baby food jar. The thermometer took about five minutes to come to temperature in the ice water bath (4 degrees C) and about ten minutes to come to temperature in the warm water bath (45 degrees C).

Answer diagram

Student Handout Questions

  1. What happened when you placed your thermometer in the warm water bath? The ice water bath? What caused the changes you observed? The liquid rose when the thermometer was placed in the warm water bath and fell when placed in the ice water bath. The changes were caused by the water increasing in volume when it was heated and decreasing in volume when cooled.

  2. What are the limitations of your thermometer? Some limitations include that the thermometer is slow to adjust to temperature because of the large amount of liquid in the "bulb" portion, that it could not measure below 32 degrees F (0 degrees C) or above 212 degrees F (100 degrees C) because the liquid being used would freeze or boil at those temperatures, and that because it is open at the top, water could evaporate (thus rendering the scale inaccurate.

  3. What other scales could you use to represent the different temperatures you measured? Temperature scales are arbitrary; just about anything can be used to represent calibration points as long as everyone in the group using the thermometer agrees on the proposed scale. Students may suggest various number ranges, birthdates of class members, names of scientists, or class members' initials.

  4. Which of the following temperatures would you prefer outside: 24 degrees Celsius or 70 degrees Celsius? Why? The best temperature for being outside would be 24 degrees C, a comfortable outdoor temperature (equivalent to 75 degrees F). Seventy degrees C would be scorching hot (equivalent to 158 degrees F).

Links and Books

Web Sites

NOVA—Absolute Zero
Considers whether there is an absolute hot, explores the impact of refrigeration on society, explains what happens to atoms when they reach ultracold temperatures, and provides student interactives related to the science of cold.

Absolute Zero and the Conquest of Cold
Features a variety of educational resources, including historical biographies, a time line of low-temperature physics, and companion teaching guides.


Absolute Zero and the Conquest of Cold
by Tom Shachtman. Boston: Houghton Mifflin, 1999.
Features the struggles of philosophers, scientists, and engineers over four centuries as they attempt to understand the nature of cold. Served as the basis for NOVA's "Absolute Cold" program.


The "Building a Bulb Thermometer" activity aligns with the following National Science Education Standards (see

Grades 5-8
Physical Science

• Properties of matter
• Transfer of energy

History and Nature of Science
• Science as a human endeavor
• History of science

Classroom Activity Author

This activity was adapted with permission from the "Absolute Zero Community Education Outreach Guide," written by Karen C. Fox in collaboration with Devillier Communications, Inc. The guide, as well as the companion "Absolute Zero Science Educator's Guide" with classroom teaching strategies, was designed for middle school teachers and informal educators. They can be found at

Teacher's Guide
Absolute Zero

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