Unit Plan 10 (Grade 8 Science): Newton’s Laws—Motion Basics
Grade 8 NGSS unit where students use force diagrams and motion graphs to show how changes in motion depend on net force and mass through hands-on investigations.
Focus: Use force diagrams and motion graphs to explain how objects move, and design investigations that show how changes in motion depend on the sum of the forces (net force) and an object’s mass.
Grade Level: 8
Subject Area: Science (Physical Science • Forces & Motion • Scientific Inquiry)
Total Unit Duration: 5 sessions (one week), 50–60 minutes per session
I. Introduction
Students begin their study of forces and motion by connecting everyday experiences—pushing a cart, riding a bike, sliding a book—to Newton’s Laws. They learn to represent forces with force diagrams (arrows showing size and direction) and describe motion using position–time and velocity–time graphs. Through guided investigations, they see how balanced forces keep motion steady while unbalanced (net) forces change an object’s speed or direction. By the end of the unit, students plan and carry out an investigation that provides evidence that the change in an object’s motion depends on the sum of the forces and its mass.
Essential Questions
- What is a force, and how can we represent forces acting on an object with a force diagram?
- How do balanced and unbalanced (net) forces affect an object’s motion?
- How can motion graphs help us describe and compare how objects move over time?
- How does the change in motion depend on both the net force on an object and its mass?
- What does a good investigation about forces and motion need in order to provide convincing evidence?
II. Objectives and Standards
Learning Objectives — Students will be able to:
- Define force, net force, and mass, and distinguish between balanced and unbalanced forces using real-world examples.
- Draw simple force diagrams (free-body diagrams) showing the main forces acting on an object in common situations (e.g., at rest, moving at constant speed, speeding up, slowing down).
- Interpret position–time and velocity–time graphs to describe an object’s motion (speeding up, slowing down, constant speed, at rest).
- Predict how changes in net force or mass will affect the change in motion (acceleration) of a cart, ball, or other object.
- Plan and carry out an investigation that changes either the net force or the mass on an object, collect data, and analyze how motion changes (MS-PS2-2).
- Use force diagrams, motion graphs, and data to construct a written or oral explanation showing that the change in an object’s motion depends on the sum of the forces and its mass.
Standards Alignment — 8th Grade (NGSS-based custom)
- MS-PS2-2 — Plan an investigation to provide evidence that the change in an object’s motion depends on the sum of the forces on the object and its mass.
- In this unit, students design and perform a simple push/pull or cart investigation, measure motion, and use diagrams and graphs to connect net force and mass to changes in motion.
Success Criteria — Student Language
- I can identify the main forces acting on an object and show them with a force diagram.
- I can explain the difference between balanced and unbalanced forces and how each affects motion.
- I can read a motion graph and say whether an object is speeding up, slowing down, moving at constant speed, or stopped.
- I can plan and carry out an investigation where I change the net force or mass, collect data, and describe what happens to the motion.
- I can use data, force diagrams, and graphs to explain how the sum of the forces and mass together affect the change in motion.