The students will be developing a model lightning detector, similar to the design used by Benjamin Franklin in his "lightning bells" experiment, which was used to alert him of passing clouds containing electricity. Though there are no available images of his actual invention, several artists' renditions illustrate a model that functions similar to the one described in this activity.

Basically, this device works using static electricity (the same electricity found in the air around a lightning storm). The electricity from the television set — mimicking the static electricity in the air — will charge one can, increasing the amount of electrons in the can that repel the electrons in the jingle bell to the far side of the bell. The now positive side of the bell is attracted to the negatively charged can and swings in that direction. Once it touches the can, the bell's charge becomes negative to match the can and the now similar charges repel the bell towards the other can. When the bell hits the other can, it loses its negative charge to the ground. Now positively charged, it is repelled away and again attracted to the charged can. This sequence continues until the bell begins to bounce from one can to the other, ringing.

• Gather materials all necessary materials.
• Make copies of the Lightning Detector Testing and Analysis Worksheet Worksheet.

Designing the Lightning Detection System

Figure 3. The set up of the model lightning detection system. click for copyright

1. Tie one end of the thread to the jingle bell, and tie the other end to the center of the wooden dowel.
2. Place the two cans upright, 2 inches apart.
3. Place the wooden dowel across the two cans (lengthwise) and tape it to the top of each can (see Figure 3). Adjust the hanging bell so that it dangles between the cans and does not touch the desk or surface.
4. Attach one of the pieces of copper wire to the first can by wrapping once around the bottom half of the can and securing with tape (see Figure 4). The other end will be attached to a metal chair, filing cabinet frame, or some other metal item to act as a ground. Note: The metal wire may need to be adjusted (bent) so that the can remains standing up straight.
5. Attach the other piece of copper wire to the second can by wrapping once around the bottom half of the can and securing with tape. Note: As with the first wire, the metal wire may need to be adjusted (bent) so that the can remains standing up straight.
6. Fold the sheet of aluminum foil in half, place the free end of the wire attached to the second can in between the layers of foil and secure with a piece of tape.

Testing and Analyzing the System

Close up of the model lightning detection system click for copyright

1. Attach the free (loose) end of copper wire attached to the first can to a metal chair, desk or filing cabinet to act as a ground.
2. Place the aluminum-foiled end of the wire (attached to the second can) flat against the screen of the television set.
3. Turn on the television to start the system. (See Troubleshooting Tips for help starting the system if it does not work.) How well does the lightning detection system work?
4. Complete the analysis provided in the associated Lightning Detector Testing and Analysis Worksheet.

1. What are the parts of the lightning detection system? Draw each part in the space provided and explain how the parts work together to make the system work.
2. How well did your lightning detector work? What would you change to improve the system? If time allows, make changes (using the extra optional materials mentioned in the materials section).
3. This is a small-scale model of a lightning detection system that uses a bell as the output for warning people if there is lightning in the area. What are other outputs that might be useful to alert people of lightning in their area? (Auditory, visual, etc.) How might you incorporate any other outputs to improve your lightning detector?
4. Think about your community. Would this be helpful to alert people in your community to lightning in the area? Where would you place this and other detectors to reach the most people?
5. Design a thunderstorm alert process for your community. Think about how you would let the most people know about the lightning in the air. Would you make more lightning detection systems or develop a way to use one or two detectors and then spread the alert to the community another way? List the steps of your process, starting with the lightning detector you just developed.
6. Time is a factor when considering lightning strikes. How long does it take for lightning to become dangerous? How quickly do you want to let people know that lightning is in their area? What would you add to the steps of the thunderstorm alert process you just outlined to reflect the time needed to alert the community?

Discussion Question: Solicit, integrate and summarize student responses to the following question.

• What causes wind and storms? (Answer: Moving air masses create wind and cause storms; air masses move from high pressure to low pressure; air masses also move when warm air rises; moving and colliding air masses cause wind and storms.)

Analysis Worksheet: Have the students complete the activity worksheet; review their answers to gauge their mastery of the subject.

Tell the Community: Have student teams create an informational brochure for the community to let them know about the characteristics of thunderstorms and the new thunderstorm alert process they have developed. If time allows, have students share their brochure with the class and engage the class in a discussion on the effectiveness of each process.

Engineering Impacts: Have students think about the impacts of having a severe weather warning system or process in place in a community. What geographical areas might need a severe weather warning system? What impacts would a severe weather warning system have on individuals or the environment? What might happen if the system fails? These are all things engineers need to consider when designing a severe warning system or process for a specific community or area.

Redesign: Allow students time to redesign their lightning detectors using their ideas on the worksheet and the extra optional materials suggested in the materials section. Reinforce the concept that engineers often iterate a design several times before determining the best possible solution to a problem. Did their second design work better than their first? Why?