Unit Plan 22 (Grade 8 Science): Energy Transfer in Systems

Focus: Explain and argue that when an object’s kinetic energy changes, energy has been transferred to or from that object within a system (e.g., collisions, friction, pushes, lifts).

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 connect their understanding of kinetic energy, thermal energy, and potential energy to the idea of energy transfer within systems. They explore everyday situations—like carts colliding, objects slowing down due to friction, and balls thrown upward—to see that whenever an object’s kinetic energy increases or decreases, energy must have flowed in or out of that object. Through demonstrations, simple data collection, energy bar models, and argument writing (CER), they practice constructing and presenting arguments about where energy came from or went. By the end of the week, students can explain energy changes in systems clearly and support their claims with evidence and reasoning.

Essential Questions

• What does it mean to say energy is transferred into or out of an object?
• How can we tell, from an object’s motion, that its kinetic energy has changed?
• In collisions, friction, and pushes/pulls, where does the energy come from and where does it go?
• How can energy bar models and system diagrams help us explain changes in kinetic energy?
• How do we construct a strong scientific argument that links evidence and reasoning to show that energy was transferred?

II. Objectives and Standards

Learning Objectives — Students will be able to:

1. Describe qualitatively that kinetic energy depends on an object’s mass and speed, and that when kinetic energy changes, energy has been transferred to or from the object.
2. Identify systems and surroundings in scenarios involving motion (e.g., collisions, friction, lifting and dropping) and track energy transfers using energy bar models or diagrams.
3. Plan or interpret simple investigations that show changes in kinetic energy (speeding up, slowing down, starting, stopping) and connect these changes to energy input or loss.
4. Construct claims about energy transfer in specific scenarios and support them with evidence (observations, data, models) and reasoning that uses energy principles.
5. Present and critique arguments (oral or written) that when kinetic energy changes, energy has been transferred between objects or between an object and its surroundings.

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

• MS-PS3-5 — Construct, use, and present arguments that when the kinetic energy of an object changes, energy has been transferred to or from the object.
  • In this unit, students use investigations, bar models, and CER writing to argue that changes in motion (and kinetic energy) require energy transfers (e.g., from pushes, collisions, friction, or fields).

Success Criteria — Student Language

• I can tell when an object’s kinetic energy changed by looking at how its speed or motion changed.
• I can use energy bar models or diagrams to show how energy was transferred into or out of an object.
• I can identify which objects in a system are giving energy and which are receiving it.
• I can write or present a scientific argument that says, “Because kinetic energy changed, energy must have been transferred,” and back it up with evidence and reasoning.
• I can explain everyday situations (like sliding, colliding, or throwing an object) as examples of energy transfer in systems.