After this activity, students should be able to:

• Explain how a thermometer works.
• Describe the physical changes that occur in a thermometer with increasing or decreasing temperature.
• Explain how engineers use thermometers in everyday applications.
• Develop a scale for measuring temperature on a thermometer they build.

When have you used a thermometer? Have you ever used one when you were sick or maybe to see what the weather was like outside? What are we looking for when we use a thermometer? (Answer: Temperature) Yes, temperature is what is measured on a thermometer. Temperature is actually a measurement of thermal energy. When we read a thermometer, we are reading a measure of how much thermal energy an object has. Microscopically, this thermal energy comes from a whole bunch of tiny little molecules bouncing around and running into each other in an object.

Who remembers what a conductor or an insulator is? A conductor of thermal energy allows heat to pass through its material, so the temperature of the object gets really hot. Materials that are good conductors of heat feel hotter to the touch than materials than are insulators, even if they are at the same temperature!

What happens when the temperature goes up in a thermometer? The liquid inside the glass tube rises. It rises because heat makes the liquid expand. When something expands, it means that it gets bigger. The opposite word for expand is to contract, or when something gets smaller. The liquid inside the thermometer contracts when the temperature gets cold. Can you think of another example when temperature makes something expand or contract? Try this at home: Blow up a balloon or a plastic bag and tie it off. Then place it in the freezer for a few minutes. What happens to the balloon or bag? (Answer: It shrinks.) What happens when you pull it out of the freezer into the warm air again? (Answer: It expands.) Different objects expand and contract at different rates. Liquids and gases expand and contract much more dramatically than solid objects, like metals or glass.

Thermometers measure temperature based on the expansion or contraction of a liquid — either red-dyed alcohol or mercury. Even though the liquid and the glass tube are at the same temperature, the liquid expands much more than the glass tube. When a thermometer touches another object, heat is transferred from the warmer object to the cooler object until their temperatures are equal. Heat transfer between touching objects is called conduction. Thermal energy always transfers from warmer bodies to cooler bodies until they are at the same temperature. If the thermometer gains thermal energy from its surroundings, the liquid in the thermometer expands. The liquid contracts if the thermometer loses thermal energy to its surroundings.

A thermometer scale is based on the freezing and boiling temperatures of water. In the Celsius scale, water freezes at 0 degrees and boils at 100 degrees. In the Fahrenheit scale, water freezes at 32 degrees and boils at 212 degrees. Degrees in the Celsius scale are larger than in the Fahrenheit scale. Scientists use the Kelvin scale, in which the lowest possible temperature is 0 Kelvin (about -273.15°C or -459.67°F), or absolute zero. Kelvin degrees are the same distance apart as Celsius degrees. Engineers use all three scales, but for different applications.

Why do you think engineers use a thermometer? Engineers need to measure the hotness or coldness of so many things they design. How would you like a refrigerator that does not keep your food cold? Yuck! Or a CD player that is so hot it melts your CDs? Engineers use thermometers to measure the thermal energy of an object that is being used by people. They must understand how much heat is being given off by a bedroom lamp or a fan. What good is a fan to cool your room if it is also heating all of the air that passes through it? Engineers also design appliances and equipment that use thermal energy to work, like ovens, heating systems and medical equipment. Engineers really need to understand how a thermometer works and how much thermal energy is being used in so many ways! Today, you are going to build your own thermometer and practice engineering by measuring the thermal energy of different conditions.

Background

Before the Activity

With the Students

1. Pour about 1/4 cup (~59 ml or 2 oz) of the alcohol-water mixture into each bottle. This should fill 1/8 to 1/4 of the bottle.
2. Add a few drops of food coloring to the mixture and swirl gently to mix.

click for copyright

3. Using a fine-point permanent marker, have the student teams use a ruler to make equally-spaced marks on the straw. They can use any division they want, as long as the marks divide the straw equally. Advise them to be careful not to bend the straw in this process.
4. Ask the students to consider how the scale on a thermometer is marked. Then, have students carefully number the marks on their straw. Their numbers can be negative or positive.
5. Direct the teams to decide on a fun unit of measurement for their straw. For example, a commercial thermometer measures in degrees Celsius, Fahrenheit or Kelvin. Have the students develop their own temperature scale name, perhaps degrees Cyndi or temperature measured in silly spots. Direct students to record their temperature scale information on their worksheets.
6. Place the straw in the bottle and hold it at the neck of the bottle without letting it touch the bottom.
7. Use modeling clay to seal the neck of the bottle so the straw stays in place. The finished thermometer should look similar to the Figure 1 diagram.

Figure 1. The activity set up to make a thermometer. click for copyright

8. Have the students wrap their hands around the bottle and observe what happens to the mixture in the bottle. Each student should record on their worksheets the thermometer reading using the numbers on their scale. For more dramatic results, place the thermometer in a tub of warm water.
9. Have each student team use a real thermometer to measure the temperature of their hands (or tub of water). Record this temperature on the worksheet next to the reading from their thermometer.
10. Have everyone take their thermometers and place them in a location away from a source of heat (a hallway instead of in the classroom, or some distance away from a heater). After several minutes, have students record the air temperature reading using their new thermometers. The teacher can provide a measurement using a commercial thermometer.
11. Move the thermometers to a source of heat (the warmer classroom instead of a hallway, or near a heater) and repeat.
12. Have the students place their thermometers in secure places around the classroom and record the temperature throughout the day. They should also record the corresponding Fahrenheit or Celsius thermometer reading, and note the times the measurements were taken.
13. Have students complete their worksheets.
14. As a class, compare and discuss the results.

- Can the students see a correlation when the temperature is cold and the fluid in their thermometer drops, or how the fluid rises when with the introduction of heat?

- Have students compare the scale on their thermometer to the scale on the real thermometer. How many units on their scale equal one unit on the real thermometer? Can they convert from one scale to the other? Can they convert from one team's scale to another team's scale?

- Explain that understanding the thermal properties of an object, including measuring the object's temperature, is important in many everyday engineering applications.

15. Have the students write a journal reflection or paragraph about the activity.

Warn the students not to drink, or even taste, the rubbing alcohol, or the alcohol-water mixture.

Make sure there is a good seal between the straw and the neck of the bottle.

Take the thermometers outside to a windy spot or in the classroom in front of a fan. How does the air movement (like wind) affect the thermometers (temperatures)?

Find the freezing temperature of water using each team's thermometer. Make an ice bath in a bucket and place each thermometer in the bath for a few minutes. Compare the temperatures for the different scales.

Have student teams prepare class presentations on different aspects of the history of the development of the thermometer, including important people: Thermoscopes, Santorio Santorio, Galileo Galilei, Daniel Gabriel Fahrenheit, Anders Celsius, Lord William Thomson Kelvin.

Dictionary.com. Lexico Publishing Group, LLC. Accessed October 5, 2005. (Source of some vocabulary definitions, with some adaptation) http://www.dictionary.com

Make a Thermometer: Watch How a Simple Thermometer Works. 2003. Science Projects, Energy Quest, California Energy Commission. Accessed October 3, 2005. (Source of activity) http://www.energyquest.ca.gov/projects/thermometer.html