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What to expect
Why does metal get hot so fast? Why do some pots have rubber handles? Every material has unique characteristics when it comes to temperature. In this activity we will explore what makes materials behave differently from one another.
Connections
In the last activity we went around the school and determined where the hottest and coldest places are. Today we will try to determine why that is. One of the major factors for temperature variations is the different building materials that the school is made out of. Every material has a specific heat capacity, which is a measure of the amount of energy that is required to increase the temperature of the material by a given amount.
How do materials influence the average temperatures and sustainability of a building?
Specific heat capacity is defined as the amount of energy required to raise the temperature of 1kg of a material by 1°C. Thermal mass describes the specific heat capacity of a material (like wood or concrete) multiplied by the density of that material.
Materials
Hair Dryer (1 per group)
Infrared laser thermometer (1 per group)
Table Scale (3 per school)
Stopwatch (you can use the app on your phone)
Instructions
Split up into small groups. We will go around the school and collect different materials. First we will look for objects inside the classroom, then go outside and find objects to test. Using a scientific formula we will find out the thermal properties (the specific heat capacity) of each object that your group collects. The specific heat capacity of a material is the amount of heat energy required to raise the temperature of a mass of a given substance by a given amount (usually one degree Celsius).
Turn on the infrared thermometer by pressing and holding the measuring button.
Press the C/F button to toggle between measuring temperature in Celsius and Fahrenheit. Use Celsius. Press the Laser Pointer icon to turn on and off the visible laser.
2. Search around your classroom to find different objects (that are small enough to weigh with the scale) to measure their thermal properties. Make sure that these items are safe to heat up and remove from the area you found them in. Return any items you take to their original spot after you are done testing them.
3. Try to find items that are entirely made of one material (e.g. erasers, wooden or rubber door stops, metal water bottles, etc.)
4. Use the table scale to measure the mass of the object (in kilograms) and write it down.
5. Point the infrared laser thermometer at the object and press the measure button. Write down the temperature it displays on the LCD display panel (make sure that you are using degrees Celsius) as the initial temperature.
6. Now heat up the object using the hair dryer and stopwatch:
(1) Put the hair dryer close to the object (without touching it) and turn it on
(2) As you turn on the hair dryer, start your stopwatch at the same time. Heat for at least two minutes.
7. Turn off the hair dryer, stop the stopwatch, and measure the temperature of the object again with the infrared laser thermometer. Write down the elapsed time (the time from your stopwatch) and the final temperature of the object in Celsius.
8. Calculate the energy used to heat up your object. The hair dryer you’re using uses about 400 Watts of electric power and converts it into approximately (but a bit less than) 400 Watts of thermal power (Watts are Joules/second).
To find the amount of energy in Joules that you used to heat up the object, use the formula: Energy (Joules) = Power (Watts) x time (seconds).
9. Now you know the energy used to heat up the object, the mass of the object, the starting temperature, and the final temperature.
Use these values and this formula to find the specific heat capacity, c.
Example
Suppose the hair dryer was used to heat up a block of steel. The hair dryer was heating up the steel for two minutes (120 seconds), and the mass of the steel was 313 grams (0.313 kg). The initial temperature of the steel was 20.4 degrees C, and the final temperature was 29.9 degrees C.
10. Go outside and collect more samples to test, like rocks or sticks.
11. Calculate the specific heat capacities of each object and record them.
12. Compare the results from the different materials that your group tested with the results from the other groups.
13. Your calculated values for specific heat capacities may not match up closely with actual values because of experimental error. All experiments have error, and some have more than others. When we used the hair dryer to heat the object, the object was not the only thing that was being heated. Much of the thermal energy output from the hair dryer was actually used to heat up the air around the object instead of the object itself.
Think about it
Specific heat capacity is important for building materials because it determines how much energy it takes to heat up an object, and how much thermal energy an object can store. After a building material warms up during the heat of the day, it can release its thermal energy during the colder overnight hours. In this activity we tested different objects and materials to explore their unique thermal properties. We used a scientific formula to calculate the specific heat capacities of these different materials and compared the specific heat capacities of a variety of different materials.
Would you want your house to be made out of a material with a higher or lower specific heat capacity?
What materials, and combinations of materials, could new buildings in your neighborhood use to to limit heating and cooling costs?
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