This resource was not designed to build towards this disciplinary core idea, but can be used to build towards it using the suggestions provided below.
Comments about Including the Disciplinary Core Idea
In The Pull of the Planets activity, students investigate how mass and size affect the gravitational pull of planets and asteroids. In the activity, spheres of differing size and mass are used to represent the object exerting the greater gravitational pull; the revolving body (a marble) remains constant throughout the investigation. To incorporate more of the core idea, teachers may wish to use a large, dense sphere (perhaps a softball) to model the gravitational pull of the Sun. Then, students could progress to using a small, dense sphere and a larger, less dense sphere to compare how moons revolve around the rocky and gaseous planets, respectively. These suggestions do not substantially change the model as presented; however, they do change the columns of the student worksheet since the gravitational wells are now being created by objects representing the Sun and planets.