Teacher Procedure:
1. To prepare for this activity, make one or several electroreceptors with your students. Have them bend the paper clip open and hook it through the pie tin so that it hangs off the bottom. Instruct them to attach the small pieces of aluminum foil to the paper clip and set the pie tin over the jar making sure the foil hangs freely and does not touch the sides or bottom of the jar. Use a piece of clear tape on either side of the jar to secure the tin to the jar.

2. Ask each child to inflate a balloon and then draw a line around the center with a marker.

3. Designate one student as the shark and ask him or her to leave the room. While the “shark ” is out of the room, choose several other children to be the shark’s “prey.” The prey then rub one side of their balloon (using the marker line as a boundary) back and forth across their hair to create static electricity. Only one side of the balloon should be used because the charge can only be held on one side. Children who are acting as prey should note which side they charged and offer that side to the shark.

4. Have the student playing the shark return to the classroom. Explain that the classroom has become a coral reef. Each balloon represents either a part of the reef or a camouflaged fish that is the shark ’s prey. The shark is unable to see the difference between balloons and the prey fish so it must use its ampullae of Lorenzini to detect the electrical charges given off by the prey. (See Background.)

5. The shark then searches your simulated coral reef by placing the electroreceptor near but not touching each balloon to find out which balloons activate the aluminum foil. Explain to the children how the homemade electroreceptor works in a similar way to the shark ’s ampullae of Lorenzini. In this activity the balloon initially has a neutral charge. Rubbing the balloon builds up the electrons (the negative charge) and creates static electricity. The aluminum pie tin also is neutral but when placed near the negatively charged balloon, its electrons are repelled. The electrons move as far away from the balloon as possible, which in this case is the hanging aluminum strips causing them to move apart.

6. This activity can be repeated as many times as you like. Simply deactivate the electrical charge in the balloons by wiping them with a damp cloth so that different children can become the prey.

Extension Activities:
Research other animals that use electricity to avoid predators or to locate prey.

Outside Resources
Sharks: The Perfect Predators
Hall, Howard. San Luis Obispo, California: Blake Publishing, 1990.

Sharks: The Super Fish
Sattler, Helen Roney. New York: William Morrow & Company, 1986.

Hammerhead Sharks
Welsbacher, Anne. Minneapolis: Capstone Press, 1995.