Students will investigate two identical self-propelled cars carrying different added masses, using repeated measurements to compare motion, speed, and acceleration. They will construct an initial force-based explanation from evidence and connect the mystery to the self-propelled car design challenge.

Students will translate evidence from the Mystery Car Evidence Challenge into measurable design criteria and constraints, investigate self-propelled car mechanisms, develop three annotated concepts, and use a weighted decision matrix to select a team design before building.

Students will build their selected self-propelled car during two dedicated build days, pass a safety and design-readiness gate, and conduct controlled preliminary trials. Teams will measure straightness, distance, time, speed, and acceleration, then calculate averages and net force and create an initial graph to guide revision in the next phase.

Students will diagnose prototype failures, use structured peer feedback to select a targeted revision, retest under controlled conditions, and organize concise visual evidence for their display card and engineering portfolio.

Students will demonstrate their self-propelled cars in a final performance challenge, explain their engineering decisions with quantitative evidence, refine showcase materials through peer feedback, and submit a concise portfolio and individual reflection.