Launch Day Tests: Bright Streamers and Double Pops

Finding Rockets, Fixing Echoes

1The Eastfield Middle School Rocketry Club launches model rockets from the school's sports field on the first Saturday of each month. A small motor sends each rocket about 150 m into the air. Near the top of the flight, a parachute and a long streamer pop out of the body tube, and the rocket drifts back down. Finding it can take a long time, because rockets often land in tall grass at the edge of the field, and last month two rockets were lost for good. Spectators have another complaint: when they stand near the gym, each launch pop seems to happen twice.

2Club advisor Ms. Farida Lindgren reminded members that light and sound are both waves. When a wave reaches a material, the material can reflect the wave (bounce it back), absorb it (take in its energy) or transmit it (let it pass through). Most materials do some of each. We see an object when light that it reflects or gives off reaches our eyes. A smooth, shiny surface such as a mirror reflects light in one direction, while a rough surface such as cloth sends reflected light out in many directions.

3On launch day, Desmond Kealoha tested five streamers of the same size. He hung them from a pole in the middle of the field on a sunny morning. Four spotters stood 150 m from the pole, one each to the north, east, south and west, and reported which streamers they could see. Then the spotters walked farther away, and the table lists the farthest distance at which any spotter could still see each streamer. A light meter measured what share of the sunlight hitting each streamer it reflected.

4Saoirse Adeyemi tested sound. Standing at the launch pad, she slapped two flat boards together to make a sharp clap, much like a launch pop. Each time, she faced a different surface, and a phone app timed the gap between the clap and its echo, a reflected sound that returns later. A teammate standing just behind each surface reported how well he could hear the clap. Saoirse repeated each clap three times and recorded the result the listeners agreed on.