Unit Plan 20 (Grade 8 Science): Potential Energy & Position

Focus: Model how gravitational, elastic, and electric potential energy depend on mass, height, and distance between objects, using diagrams and scenarios to show how energy is stored and transformed.

Grade Level: 8

Subject Area: Science (Physical Science • Energy • Forces & Interactions)

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

I. Introduction

Students shift from energy of motion to the idea of stored energy—potential energy—in fields and systems. They explore how gravitational potential energy depends on an object’s mass and height, how elastic potential energy depends on how far something is stretched or compressed, and how electric potential energy depends on the distance between charged objects. Through diagrams, models, and simple investigations, they show how changing position in a field or system changes the amount of energy available to be converted into motion. By the end of the week, students can use models to explain how potential energy is stored and how it depends on mass and distance.

Essential Questions

• What is potential energy, and how is it different from kinetic energy?
• How do mass and height affect gravitational potential energy in systems like ramps, shelves, and roller coasters?
• How does the amount an object is stretched or compressed affect elastic potential energy (springs, rubber bands, bows)?
• How does the distance between charges affect electric potential energy in attractive and repulsive situations?
• How can models (diagrams, graphs, energy bar charts) help us describe how stored energy changes as positions in a system change?

II. Objectives and Standards

Learning Objectives — Students will be able to:

1. Define potential energy qualitatively as stored energy that depends on an object’s position or configuration in a system (e.g., height in a gravitational field, stretch in a spring, separation of charges).
2. Develop models for gravitational potential energy showing how it increases with mass and height above a reference level.
3. Develop models for elastic potential energy that show how it increases as a spring or rubber band is stretched or compressed more.
4. Develop models for electric potential energy that show how it depends on distance between charged objects (with different patterns for attractive vs. repulsive situations, qualitatively).
5. Use diagrams, bar models, and/or simple graphs to describe how changes in position in a system change the amount of stored potential energy and can be converted to kinetic energy.
6. Explain real-world examples (e.g., falling objects, archery, charged balloons) using potential energy models that connect mass, height, and distance between objects to stored energy.

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

• MS-PS3-2 — Develop a model to describe how stored potential energy depends on mass, height, and distance between objects.
  • In this unit, students create and interpret models of gravitational, elastic, and electric potential energy that show how changing position or mass changes the stored energy in a system.

Success Criteria — Student Language

• I can explain that potential energy is stored energy that depends on position or arrangement, not just motion.
• I can use a model to show that gravitational potential energy increases when mass or height increases.
• I can use a model to show that elastic potential energy increases as a spring or rubber band is stretched/compressed more.
• I can describe how electric potential energy changes when charged objects move closer together or farther apart.
• I can use diagrams, bar models, or graphs to tell a clear story of how changing position changes stored potential energy in real situations.