Choose the system
Identify which object or collection of objects your diagram describes.
AP Physics 1 · Unit 2, Part 1 · Forces
Free-Body Diagrams
Choose an object, identify its interactions, and build force diagrams that explain equilibrium and acceleration.
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- Self-paced
Start guided lesson
Learn by doing
Three ideas you’ll put into motion
Draw the forces
Separate weight, normal force, tension, friction, and applied forces from motion arrows.
Connect force and motion
Use the net force to predict the direction of acceleration and check your reasoning.
The big idea
The key ideas, at a glance.
An arrow represents an interaction
A free-body diagram includes the external forces acting on the chosen system. Velocity and acceleration are separate quantities.
Net force is the vector sum
Combine forces with their directions. Balanced forces produce zero acceleration; unbalanced forces determine acceleration’s direction.
A quick comparison
A block rests on a horizontal surface with no other vertical interactions.
Normal force and weight act on the block.
Teaching this topic?Classroom fit, AP connections, and support
- Classroom fit
- Use for a concept introduction, guided independent practice, or a projected class discussion.
- Before students begin
- Recognize vector directions and add signed quantities. The lesson introduces the force types.
- Built-in support
- Prepared scenes, guided prompts, and feedback on lesson questions.
- AP Physics 1 connections
- Unit 2: systems, interactions, force representations, and Newton’s laws.
- Check for understanding
- Ask students to name the other object responsible for each force they draw.
- Optional extension
- Investigate forces further in the Net Force and Acceleration lab.
Ready to test your thinking?
The first scene is set up. Start the lesson and explore.