Unit Plan 12 (Grade 8 Science): Gravity & Gravitational Interactions

Focus: Argue from evidence that gravitational interactions are always attractive and depend on the mass of interacting objects (and distance, qualitatively), using everyday phenomena and space science examples.

Grade Level: 8

Subject Area: Science (Physical Science • Forces & Motion • Scientific Argumentation)

Total Unit Duration: 5 sessions (one week), 50–60 minutes per session

I. Introduction

Students deepen their understanding of gravity as a force of attraction between any two objects with mass, not just “things falling down.” They explore gravity in everyday contexts (falling objects, weight, jumping) and in space contexts (planets, moons, satellites) to see that gravitational interactions are always attractive and that the strength of the interaction depends on the masses of the objects (and distance between them). Through hands-on demonstrations, data analysis, and structured claim–evidence–reasoning tasks, students construct and present arguments that support the claim that gravity is always attractive and mass-dependent.

Essential Questions

• What is gravity, and how is it different from other forces we experience?
• How do we know that gravitational interactions are always attractive (never pushing objects apart)?
• How does the mass of objects (and distance between them) affect the strength of gravitational interactions?
• How can we use evidence from everyday life and from space science (planets, moons, satellites) to argue for a model of gravity?
• What makes a scientific argument convincing and well supported?

II. Objectives and Standards

Learning Objectives — Students will be able to:

1. Describe gravity as a force of attraction between any two objects that have mass, acting at a distance.
2. Explain, using everyday and astronomical examples, that gravitational interactions are always attractive (objects pull toward each other).
3. Use data and information (e.g., weight on different planets, planetary masses, orbital patterns) to show how gravitational interactions depend on mass (and qualitatively on distance).
4. Identify and critique common misconceptions about gravity (e.g., only on Earth, heavier objects fall faster, gravity pushes things down).
5. Construct a written and/or oral argument that gravitational interactions are attractive and depend on mass, using claim–evidence–reasoning structure.
6. Present and defend their argument to peers, responding to questions and counterexamples using additional evidence.

Standards Alignment — 8th Grade (NGSS-based custom)

• MS-PS2-4 — Construct and present arguments using evidence to support the claim that gravitational interactions are attractive and depend on mass.
  • In this unit, students gather and analyze evidence from falling objects, weight comparisons, and planetary data to build and present a scientific argument about gravity.

Success Criteria — Student Language

• I can explain that gravity is always attractive—objects with mass pull on each other, they do not push apart.
• I can give examples on Earth and in space that show how more massive objects have stronger gravitational interactions.
• I can use data (like weight on different planets or orbital patterns) as evidence in my argument.
• I can write or present a clear claim–evidence–reasoning argument that gravity is attractive and depends on mass.
• I can respond to a challenge or question about gravity using scientific ideas and evidence, not just opinion.