Activity 3.3 An Energy Investigation

How Much Energy Arrives in your School Yard?

In this activity you will allow a bottle of water to absorb the sun's energy. You will be able to calculate how much energy is absorbed by observing how much the temperature changes inside the jar, and applying a formula. For this to work right, the jar must be set up directly facing the sun to absorb the sun's energy as efficiently as possible. The water inside the jar should be at the outdoor air temperature to minimize heat gains or losses to the surrounding air during the experiment. Any energy that leaks from the jar into the surrounding air will cause your measurements to be less accurate.

If your water is colder (or hotter) than the outdoor air temperature, you should set up a second, identical jar in the shade, record its start and stop temperatures and subtract this temperature difference from your exposed jar temperature difference. For example, if your exposed jar experienced a temperature increase of 5 degrees C and the shaded jar experienced a temperature increase of 2 degrees C, then the temperature increase due to the sun and NOT the surrounding air is: 5C - 2C = 3 degrees C.

Problem: How much energy does your school yard receive from the Sun?
                  How does the amount of energy received from the Sun depend on your location?

Equipment:

• one shielded alcohol thermometers provided in the GLOBE equipment.
• a widemouthed CLEAR plastic or glass jar with leakproof screw lid
• a piece of black plastic cut from the cover of a report folder or a black trash bag.
• meter stick
• watch or timer
• data sheet
• 1 to 2 gallons of water
• a large beaker for measuring the volume of water, scaled in ml


Procedure: Conduct this procedure three times, on three clear sunny windless days. Try to conduct the experiment at midday, between 10 am and 2 pm.

1. Prepare the jar: Line the inside of one half of the jar with the black plastic, using rubber cement to hold the plastic in place if necessary.
2. Fill the jar completely with a measured volume of water. The water should be the same as the temperature of the outside air. Record the volume of water used on the data sheet.
3. Hang the thermometer on a piece of light string inside the jar. Allow the string to droop over the mouth of the jar to the outside. Put the lid on the jar and screw it on tightly, catching the string in the threads. (See diagram.)
4. You are ready to place the jar in a sunny location. First read the thermometer inside the jar and record this as the starting temperature. Prop up the jar at an angle with books or rocks (anything) so that it directly faces the sun. You will want the maximum amount of black area on the back side of the jar to be directly exposed to the sun, and the sun's ray should strike the area perpendicularly. As you place the jar, allow the thermometer to roll over, face down, so that the metal cover shields the thermometer from the direct rays of the sun.
5. It would be of interest if you could use a protractor to measure the angle between the ground and the face of the jar. Include this angle in your lap report. We will compare the different angles students use at different locations.
6. Wait exactly 20 minutes. Pick up the jar and swirl it gently to thoroughly mix the water. Be careful not to bang the thermometer around. Without opening the jar, read the thermometer to the nearest 0.1 degree Celsius. Record this temperature on the data sheet as the ending temperature.
7. Use the formulas on listed under calculations to calculate the energy added to the water in the jar by the sun.
8. Write a report about your investigation. Use the Checklist for Student Lab Report as a guide. Include the following parts.
• title
• problem
• equipment and procedure
• data
• calculations
• discussion of your results
• conclusions
• new questions

  Data Table

            Click here for the Data Table 

Writing Lab Reports

• Developing Laboratory Report Writing Skills

 Extending Your Understanding

Think about what you've observed about heat energy and temperature. Discuss the following questions with other students and your teacher.
1. You learned that when the sun is shining, every part of the Earth receives the same amount of energy from the sun. How would things be different if the Earth was flat?
2. You have learned that warm air rises. Then why is it cold on a mountain top and warm in the valley?
3. Give an example of a situation where you add energy and the temperature does not change.
4. One gallon of water at 30 deg. C. will melt 46 icecubes. A half gallon of water at the same temperature will only melt 23 icecubes. Explain.
5. When the stars twinkle in the nighttime sky, do planet twinkle also? Does an astronaut orbiting the Earth see twinkling stars and planets?

 Test your Understanding

1. What is the difference between temperature and energy?
2. What is the source of most of the energy we humans, animals, and plants use here on Earth?
3. Explain why the sun feels much hotter at noon than it does at 8:00am in the morning.
4. The temperature of a glass of water was 25.0 degrees C. After sitting in the sunshine for 20 minutes the thermometer read 29.5 degrees C. Calculate T.
5. Using the information in question number 4, what other information would you need to calculate the heat energy added to the glass of water?
6. If all the TSA schools, from north and south, east and west, measured the amount of energy arriving in their school yards very carefully, using the proper method, how would their measurements compare?
7. Name three factors that affected your measurement of the sun's energy arriving in your school yard.