Using an assortment of playground and toy balls, students will measure diameter, calculate distance and scale, and build a model of the Earth-Moon system. Materials Two round balloons (at least 8-inch size, preferably 12-inch size) Full-size men’s basketball (or a beach ball or other ball about 75 cm in circumference) Tennis ball or baseball Balls of assorted sizes (marbles, tennis balls, golf balls, table tennis balls, softballs, plastic toy balls, basketballs, soccer balls, volleyballs, etc.)