An unbalanced force acting on an object changes its speed or direction of motion, or both. If the force
acts toward a single center, the object’s path may curve into an orbit around the center. (BM, grades
6–8, 90)
From activities with trajectories and orbits and using the Earth-Sun-Moon as an example, students
can develop the understanding that gravity is a ubiquitous force that holds all parts of the solar system
together. (NS, grades 5–8, 159)