After this activity, students should be able to:

• Define heat capacity.
• Explain how heat capacity determines a material's ability to store thermal energy.
• Measure the temperature of a material over time.
• Describe the difference between materials with high-heat capacity and low-heat capacity.
• Understand that materials with high-heat capacities store thermal energy better than materials with low-heat capacities.
• Determine which material has the highest heat capacity and, thus, stores thermal energy well.
• Explain why engineers need to know about the heat capacity of materials when designing equipment, structures and products.

Today, we are talking about thermal energy or heat energy. Have you ever been outside on the playground on a sunny day and touched the metal of a swing set? How does it feel? It is hot? Yes! How about walking barefoot on a sunny day? Have you ever walked on the sidewalk and had to jump to the grass because the pavement was too hot for your feet? Do you think the grass and the pavement are actually different temperatures — even if it is the same temperature outside? They probably are not different temperatures at all!

Different objects require different amounts of heat to raise the same amount of material to the same temperature. You can notice this on a hot summer day when the ground is cool enough to walk on, but the road and sidewalk are very hot, or a metal bench is much hotter than a wooden bench. The metal bench requires less heat to make it hot than the wooden bench. When we measure this property, the quantity is called the heat capacity of he material. When an object absorbs heat, the thermal energy is spread among the atoms and molecules in the material. Energy makes the molecules vibrate back and forth. If the vibrations become faster, we measure it as an increase in temperature. Every material has a different heat capacity.

Another way of explaining a materials' heat capacity is to think about it as the measurement of thermal energy storage, just like temperature is the measurement of thermal energy given off. Heat capacity is how much thermal energy a material stores up and temperature is how much thermal energy a material gives off. Today, we are going to look at the heat capacity of some different materials.

Engineers use their knowledge of the thermal properties of matter to design everything from engines to satellites to houses. Engineers use a material's heat capacity to determine its usefulness for different applications. A material with a low-heat capacity (such as metals) has a greater increase in temperature from absorbing the same amount of heat as a material with a high-heat capacity (such as water). This is why materials with high-heat capacities, such as water, are used for storing thermal energy. Other materials with high-heat capacity, such as brick or concrete walls, are important to engineers designing houses that they want to stay warm in cold climates. Engineers consider heat capacity when working with any material. For example, think of all the devices and appliances in your house. If the wiring in your computer or lamp or hair dryer gets too hot, it may spark and stop working.

Before the Activity

With the Students

1. Divide the class into student teams of three or four students each.
2. Assign team "jobs." In each team, have one student in charge of reading the temperature on the thermometer in the material, another to read the temperature in the water and a third to be the recorder. If you have any groups of four, have the fourth student be in charge of watching the time between measurements.
3. Ask the students to predict which material will have the highest heat capacity (store thermal energy the best), and record this on their worksheets.
4. Have each team go to the appropriate station and look at their materials. Instruct them to measure 200 ml of their assigned material using a measuring cup or jar with the 200 ml level marked.
5. Have the student testing water pour the hot water in his/her container (large jar) and place a thermometer in the container. Have students testing the powdered material, sand or dirt, fill the beaker halfway (small jar), place a thermometer into the material and then finish filling their containers. The material must cover the thermometer bulb or bottom.
6. Using masking tape, label each container.
7. Measure and record the initial temperatures of the materials and water. Remind the recorders to document the starting temperatures on their worksheets.
8. Place the beakers/jars of material into the large container of hot water.
9. Have students measure and record the temperature of the material and the water bath every minute for 10 minutes (see Table 1 for a sample data table). Record the starting temperature of the 200 ml beaker of water, sand, and paper, etc., and the temperature of the hot water bath at "0" minutes. Record the temperature reading of each of the thermometers every 1 (or 2) minutes in the table. Record the temperature reading of each of the thermometers every 1 (or 2) minutes in the data table.

Table 1. Sample data table of temperature readings of different materials in an ice bath. click for copyright

10. Have each team member pour the contents of their beaker/jar into waste containers at the appropriate station.
11. Repeat the entire activity using ice water instead of hot water.
12. After all measurements have been made, direct students to make a bar graph showing their material and the highest temperature or the lowest temperature it reached.
13. Conclude with a class discussion:

• Compare the results of the different materials tested. Compare graphs. Which materials had the highest heat capacity (stored heat the longest)?
• Also compare the temperature gains (losses) to the teacher's measurement of the hot water and ice water, taken as a control. Discuss the water's heat loss (and gain) to (and from) the air in the room.
• Ask students to comment on their initial predictions, as recorded on the worksheets. What have they learned? Ask them to explain their understanding of which materials have a high-heat capacity and which have a low-heat capacity.
• How would an engineer use what the students have learned today? Which of the materials that the class measured would an engineer choose for insulating a home in the winter? To design a good food storage container for soup? For the design of a product that you want to heat up quickly?

Caution students to pour dense materials, like sand, powdered concrete or dirt, into the container first, place the thermometer in the container and then continue filling it.

Students should not force a thermometer into a dense material because the thermometer might break.

Some materials, like sand (after being used) need to be collected in a separate container until they return to room temperature, since they may be cold or warm for a while as a result of the experiment. Dense materials gain and lose heat slowly. To obtain the correct amount of materials, students can estimate the 200 ml of sand or other materials in a 250 ml beaker.

Obtain the hot water from the tap (around 85°C) or the teacher can heat a larger container of water (85°C) and distribute the water to students.

If time, direct students to either record the number of minutes each material took to lose a two degree increase in temperature after the heating occurred, or to record how long each material took to gain two degrees in temperature after being cooled.

Have the students complete the activity again, bringing in other odd materials from home. Create a class list ranking the heat capacity of different materials from greatest to least.

Have students make a thermos using a small jar inside a large jar with one of the materials from this activity as the buffer around the small jar. Have the students place hot or ice water inside their thermos and measure the temperature in regular intervals to see how effective the thermos is.

Testing Thermal Storage Materials Lesson Plan. Renewable Energy Lesson Plans, Infinite Power, Texas State Energy Conservation Office. Accessed October 5, 2005. (Source of activity) http://www.infinitepower.org/lessonplans.htm