Nearly every problem this year uses some combination of these six forces. Learn to recognize them on sight.
🧭 Plot Summary
All of Unit 1 described motion without ever asking what causes it. Unit 2 asks exactly that question, and the answer is always the same word: force — a push or a pull, with both a size and a direction, measured in newtons (N).
The tool you'll use to organize every force problem from here forward is the free-body diagram (FBD): isolate the object as a single point, then draw every force acting on it as an arrow pointing the right way, sized roughly to its strength. Get the diagram right, and the physics underneath it gets dramatically easier. Get it wrong, and nothing that follows will make sense.
What you will do in this lesson
- Shift from Unit 1's question (how is it moving?) to Unit 2's question: why is it moving that way?
- Meet the standard cast of forces: gravity, normal, applied, tension, friction, and air resistance.
- Learn the free-body diagram convention: isolate the object, draw every force as an arrow from that point.
- Practice finding net force by combining arrows, and recognizing equilibrium when it appears.
- Build the one diagram you'll rely on for the rest of this course, done correctly from day one.
Why it matters
Every activity, project, and problem for the rest of this unit assumes you can draw a correct free-body diagram without being told how. This is the one skill everything else in Unit 2 gets built on top of.
✅ Self-Check Before You Roll On
Check off each item as you get there. These are not grades — they are your own signal.