Byline: Jeremy Brown and John Corbin
Teachers are familiar with dozens of high school physics activities involving eggs. In this egg-related activity, students design and construct "Egg Racers" to learn problem-solving, physics, and engineering skills.
About 15 years ago, we set out to culminate a unit on electromagnetism with a project that involved electric motors. Inspired by the Massachusetts Institute of Technology design contests, we divided students into teams, provided each team with a bag of parts (e.g., motors, connectors, battery clips, sticks, switches), and directed the teams to build a machine that would score goals by hitting targets inside a homemade hockey rink. Since that first in-school design contest, we have tried several different projects. The most challenging, competitive, and engaging project has been the "Egg Racer."
The Egg Racer project requires students (individually or in teams of two) to construct a vehicle to carry a chicken egg a distance of 3 m toward a terminal barrier (the wall) as fast as possible and stop before colliding with the barrier. [Note: Science Olympiad has a similar competition called the "Scrambler," which uses a falling mass for drive mechanism energy.] For the Egg Racer project, students are supplied with two 9V batteries, two DC motors, two paint-stirring sticks (donated by a local building supply store) for the vehicle chassis, two old CDs (as wheels), two snap battery connectors, and a simple slide switch. Small DC motors and other supplies suitable for this project can be obtained from a variety of vendors. The voltage rating for the motors is not critical and the cost varies from $1 to $2 each.
Students may supply their own wheels, to be used in addition to the CDs, and other miscellaneous parts such as gears, supports, or parts from toys (remote-controlled cars or parts are not allowed). Students are allowed four to five classroom periods for construction and another two periods for testing the finished product. Figure 1 shows an example of an egg racer. Students are not allowed to take their racers home to work on; however, they may consult with other people and resources for ideas and moral support.
An example of a student Egg Racer (notice the egg at the front of the car).
Vehicles are judged on the amount of time needed to cover the 3 m, the amount of deviation from a straight line path, smoothness of operation, and stopping distance from the barrier. Hitting the barrier or dropping the egg en-route disqualifies the car for that run. [Note: The function of the egg is only to add suspense and risk to the endeavor. Any object, or no object at all, would suffice.] As a quantitative assessment, a scoring rubric provides feedback on the effectiveness of each vehicle (Figure 2). The best run out of three trials is taken for the final score.
Egg Racer scoring rubric.
Simple taped connection
Egg is attached with rubber band; egg is firmly held in place
Egg is easy to insert and remove; extends about 2 cm; egg is firmly held in place
Same as 3 with exceptional quality
Moves within boundaries toward front wall
Straight and smooth forward motion, slight deviation
Straight, smooth, fast with no sidewise deviation
Stopping mechanism included
Stops vehicle outside of 0.5 m range
Stops vehicle inside 0.5 m range
Stops vehicle inside 10 cm range
Poor power to drive mechanism, wobbles, intermittent drive
Little slippage of drive mechansim, slight wobbles
Smooth energy transfer, but slow moton of drive mechanism
Smooth energy transfer to drive mechanism
All recyclable parts returned in good shape
The race track
The track is laid out on the floor of the physics lab and is 4 floor tiles wide x 10 floor tiles long. …