AP Physics C: Mechanics · Unit 4 · Topic 4.1
Linear Momentum
Impulse integrals and system momentum describe collisions, center-of-mass motion, and changing-mass models.
1. Topic Lens
Linear Momentum is studied through linear momentum. Connect the system boundary, interacting parts, and measurable evidence before applying a formula.
2. Why the Formula Works
The relationship is built from definitions and conservation reasoning:
- Sum particle momenta to define total system momentum P.
- Internal force pairs cancel in the system sum under Newton's third law.
- Only net external force remains, so integrating it gives the system momentum change.
3. Detailed Visual Model
4. Worked Example and Lab Link
A 10 N force acts for 0.20 s in one direction. Find the impulse.
Answer: J=(10)(0.20)=2.0 N·s in the force direction.
Investigation idea: Use high-frame-rate video to reconstruct two-dimensional momentum vectors before and after a collision.
Common trap: Momentum conservation applies to a defined system with negligible external impulse, not automatically to each object.
Explain how linear momentum supports or limits this conclusion: J=(10)(0.20)=2.0 N·s in the force direction.
Official curriculum reference: College Board AP Physics C: Mechanics course page. The explanation and worked example are independently written for this study site.