The Great Gravity Escape

Geoffrey Hill; Daria Kotys-Schwartz; Chris Yakacki; Malinda Schaefer Zarske; Timothy M. Dittrich; Janet Yowell
Type Category
Instructional Materials
Lesson/Lesson Plan , Model
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 Great Gravity Escape is an outdoor based, kinesthetic activity designed to illustrate the role of gravity and velocity in orbital interactions by calculating the escape velocity for a water balloon “spacecraft” orbiting a student. The activity utilizes a twine/clothespin apparatus to represent the force of gravity while spinning motions represent velocity. It would be helpful if students are familiar with Newton’s Laws of Motion prior to starting this activity.

Two safety notes:  since balloons are being used, teachers should check for latex allergies and safety glasses should be worn during the activity. The activity can be completed in one period; however, an additional period might be needed for discussion.

Intended Audience

Educational Level
  • Grade 8
  • Grade 7
  • Grade 6
  • Middle School
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
In this activity, students are using, not developing, a model to investigate the role of gravity within a system. Although the activity limits itself to investigating the actions of orbiting spacecraft, the same scientific principles apply to the motions of moons, planets and even solar systems in the universe. Prior to the lesson, teachers should introduce the concepts of gravity and velocity (and how it differs from speed). Since the activity concerns itself with calculating escape velocities, teachers will need to emphasize that escape velocity is a function of both gravity and velocity. For example, teachers should check to see that students understand which part(s) of the model represents these two forces. Students should recognize that the spinning actions represent velocity; however, students may have difficulty relating the twine/clothespin apparatus to gravity.

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
After completing the activity and analyzing their results, students should be encouraged to modify the model in order to gain additional insights. For example, the Activity Extensions suggest that students change the mass of the balloon. How might the escape velocity change if mass was modified? Would there even be a discernible difference? In addition, how does decreasing or increasing velocity change the effect of gravity on an object? Teachers should stress to students that only one variable should be changed during each iteration of the model and that students must document how the variable has been changed. Students should be encouraged to predict the effects of these changes prior to implementing them.

Disciplinary Core Ideas

This resource appears to be designed to build towards this disciplinary core idea, though the resource developer has not explicitly stated so.

Comments about Including the Disciplinary Core Idea
Because this activity tasks students with calculating the escape velocity for a man-made satellite (balloon), teachers will need to reinforce that this scenario also applies to the forces that exist between the Sun and planets. The attractive force of gravity between the Sun and a planet and the velocity of the planet are both responsible for its orbit.

Crosscutting Concepts

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

Comments about Including the Crosscutting Concept
The activity requires that students use the model to calculate the escape velocity of the water balloon. In order to underscore the importance of the balance between gravity and velocity in this process, teachers should ask students to explain and point out how these forces are represented in the model. Teachers might also consider designing an open-ended question that tasks students with explaining how this model specifically represents these forces and how changes in these forces will affect escape velocities.

Resource Quality

  • Alignment to the Dimensions of the NGSS: The Great Gravity Escape is strongly aligned to all three dimensions of the NGSS. Students work with a model of an orbiting object (Practice and Crosscutting Concept) to discover the relationship between the forces (gravity and velocity) involved in keeping that object in orbit (Disciplinary Core Idea). Although the activity emphasizes calculating escape velocities, teachers can easily shift the activity’s focus to an emphasis on the forces involved. For example, teachers can pose questions that direct student attention towards these forces. Teachers can encourage students to think of modifications to the model, providing opportunities to develop both the Practice and Crosscutting Concepts of using models to investigate the core idea.

  • Instructional Supports: The kinesthetic aspect of the activity allows students to experience an authentic, relevant scenario (as directly as possible) involving forces in the solar system. The activity uses scientifically accurate and grade appropriate information to present the phenomena of orbital interactions. Students are afforded multiple opportunities to express their ideas and receive feedback within their groups. The authors do not provide any guidance to support differentiated instruction. Teachers will need to make accommodations for students with physical disabilities.

  • Monitoring Student Progress: The lesson plan includes pre-activity, activity-embedded and post-activity assessments. The embedded activity assessment consists of calculating escape velocities and is not useful in monitoring 3 dimensional student performance. Instead, teachers should monitor the student groups during the activity to check whether students are utilizing the model correctly both when implementing the lesson as written and when introducing different variables as suggested in the Practices section. The authors do not include aligned rubrics nor scoring guidelines.

  • Quality of Technological Interactivity: The Great Gravity Escape is a hands on, kinesthetic activity. There is no technological interactivity.