A Hand-Powered Signal for the Produce Shed

Testing a Signal for a Produce Shed

After visiting a farm's produce shed, a class built a classroom model of a warning signal. A worker would turn a crank to light the signal before moving a produce cart. The model had to work without a battery or wall outlet. Its red light had to be visible from at least 8 feet away in every trial.

Moving objects have energy of motion. A generator can use motion to produce electrical energy. A lamp uses electrical energy to give off light. A buzzer uses electrical energy to make sound. A reflective hood redirects light; it does not produce electricity.

Step 1: The teacher supplied an enclosed, low-voltage hand-crank generator, snap-together wires, and a red lamp. Students connected these parts. They used smooth, ready-made reflective hoods. They did not cut materials or use farm machinery.

Step 2: The class compared three designs. Design A had no hood. Design B had a flat reflective hood behind the lamp. Design C had a curved reflective hood behind the lamp. Students kept the same generator, wires, and lamp. The hood was the only part they changed.

Step 3: For each trial, Tessa turned the crank once each second, following a steady beat. The lamp always pointed down the same shaded aisle. The same observer started near the lamp and walked backward along distance marks spaced 2 feet apart. The class recorded the farthest mark where the observer could still see the light.

Step 4: The class tested each design three times. Design A's results were 4, 4, and 4 feet. Design B's results were 6, 6, and 6 feet. Design C's results were 10, 8, and 10 feet. To judge dependable performance, students graphed the shortest distance recorded for each design.

Step 5: Students also tried turning the crank more slowly. The lamp became dimmer. When the crank stopped, the lamp went dark. The device had no part that stored electrical energy. All visibility trials took place in dry, shaded conditions.