Students explore the use of wind power in the design, construction, and testing of "sail cars," which, in this case, are little-wheeled carts with masts and sails that are powered by the moving air generated from a box fan. The scientific method is reviewed and reinforced with the use of controls and variables, and the engineering design process is explored. The focus of the activity is on renewable energy, as well as the design, testing, and redesign of small cars made from household materials. The activity (and an extension worksheet) includes the use of kinematic equations using distance, time traveled and speed to enforce exponents and decimals. This engineering curriculum meets Next Generation Science Standards (NGSS).