The Pull of the Planets

Lunar and Planetary Institute
Type Category
Instructional Materials
Lesson/Lesson Plan , Activity
This resource, vetted by NSTA curators, is provided to teachers along with suggested modifications to make it more in line with the vision of the NGSS. While not considered to be "fully aligned," the resources and expert recommendations provide teachers with concrete examples and expert guidance using the EQuIP rubric to adapted existing resources. Read more here.



The Pull of the Planets is part of a thematic series of lessons highlighting the Juno mission to Jupiter. It is a traditional hands on activity that models how gravitational forces can keep planets and asteroids in orbit within the Solar System. Using a stretchable fabric held in place with an embroidery hoop, students work with spheres of various materials to explore how mass and size affect the strength of gravitational forces. Background materials, including a materials sheet, aid teachers in organizing this activity.

Intended Audience

Educational Level
  • Middle School
  • Grade 8
  • Grade 7
  • Grade 6
Access Restrictions

Free access - The right to view and/or download material without financial, registration, or excessive advertising barriers.

Performance Expectations

MS-ESS1-2 Develop and use a model to describe the role of gravity in the motions within galaxies and the solar system.

Clarification Statement: Emphasis for the model is on gravity as the force that holds together the solar system and Milky Way galaxy and controls orbital motions within them. Examples of models can be physical (such as the analogy of distance along a football field or computer visualizations of elliptical orbits) or conceptual (such as mathematical proportions relative to the size of familiar objects such as students' school or state).

Assessment Boundary: Assessment does not include Kepler’s Laws of orbital motion or the apparent retrograde motion of the planets as viewed from Earth.

This resource is explicitly designed to build towards this performance expectation.

Comments about Including the Performance Expectation
The Pull of the Planets is a hands-on activity that provides qualitative information on the role of gravity in our Solar System. The lesson, as written, focuses on the gravitational forces of planets and asteroids; however, teachers can easily reassign the materials to represent planets, their moons and even the Sun. In this activity, students model gravitational forces using materials of different sizes and masses. Students are not designing a model; rather, the directions specify the type of materials used by the students. Groups may experience varying degrees of success in having the marbles orbit the asteroids and planets. Therefore, teachers should caution that this model simply points to the relationship between the mass and size of an object and its gravitational pull.

Science and Engineering Practices

This resource is explicitly designed to build towards this science and engineering practice.

Comments about Including the Science and Engineering Practice
In this activity, students use a traditional model to explore the gravitational pull of planets and asteroids. As noted above, students are working with an established model; they are not designing their own. In order to bring this activity into closer alignment to the practice, teachers may task students with deciding what types and sizes of materials should be used. Students should be ready to justify their choices. Alternatively, teachers may wish to have students just brainstorm changes to the activity with an emphasis on material selection. For example, how would materials of significantly different masses affect the model?

Disciplinary Core Ideas

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.

Crosscutting Concepts

This resource is explicitly designed to build towards this crosscutting concept.

Comments about Including the Crosscutting Concept
Teachers should emphasize the predictive nature of the model presented in this activity. By tweaking the provided worksheet, teachers could require that students predict the outcome of using different materials to create gravitational wells and to provide justifications. If students continue to have difficulty making the cause and effect connection between mass, size and gravitational forces, teachers may consider adding additional spheres of differing size and mass. For example, a dense metallic sphere or a mid-size Play-Doh sphere may provide additional evidence to explain gravitational forces.

Resource Quality

  • Alignment to the Dimensions of the NGSS: Although The Pull of the Planets is included in a group of activities to support the Juno mission to Jupiter, the activity itself can be used to model gravitational forces between any two objects. In the activity, students explore the effect of two variables, size and mass, on gravitational pull by comparing spheres of different diameters and densities. The activity is strongly aligned to both the core idea and cross cutting concept. Its weakness lies in the area of scientific practice: students are not developing a model; rather, they are utilizing a traditional classroom model of gravitational pull.

  • Instructional Supports: As written, The Pull of the Planets does not provide opportunities for students to explain their observations and conclusions. The activity is grade appropriate; however, there is no support for differentiation. The website provides Facilitator's Notes, background information and a shopping list for supplies.

  • Monitoring Student Progress: Formative assessments and rubrics are not included with the activity. There is a link to a student worksheet; however, teachers might wish to add additional columns where students are required to record and explain their observations. Alternatively, teachers may want to construct writing prompts for students to use in their journals.

  • Quality of Technological Interactivity: The Pull of the Planets is a hands on activity.