Unit Overview
Momentum Overview
AP Physics 1Β· 5 min read π 12-18% of total AP exam score
1. Unit at a Glance
This unit builds from core definitions up to a powerful problem-solving framework that simplifies analysis of interactions between objects. Momentum conservation is one of three fundamental conservation laws you will use across all of AP Physics 1, and it applies to any system with no net external force.
We progress from foundational concepts to increasingly complex applications: starting with core definitions, the impulse-momentum theorem, and momentum conservation, before moving to one-dimensional and finally two-dimensional collision problems.
This unit is organized into the following sub-topics:
AP Physics 1 Conservation of Momentum for Isolated Systems
Explains the conditions for momentum conservation and applies the law to isolated interacting systems.
β β β± 8 min
AP Physics 1 Impulse-Momentum Theorem
Connects change in an object's momentum to the net impulse exerted by external forces over time.
β β β± 9 min
AP Physics 1 Momentum and Impulse
Introduces foundational definitions of linear momentum and impulse as vector quantities.
β β± 7 min
AP Physics 1 One-Dimensional Collisions
Applies momentum conservation to elastic and inelastic collisions along a single axis.
β β β β± 12 min
AP Physics 1 Two-Dimensional Collisions
Extends momentum conservation to glancing and other collisions that occur in two dimensions.
β β β β β± 15 min
2. Common Pitfalls
Wrong move:
Applying momentum conservation to systems with a non-zero net external force.
Why:
Momentum is only conserved for isolated systems with no net external force acting on the system.
Correct move:
Always check for net external force first before using momentum conservation.
Wrong move:
Assuming kinetic energy is conserved in all collisions.
Why:
Only elastic collisions conserve kinetic energy; all isolated collisions conserve momentum.
Correct move:
Confirm collision type before applying kinetic energy conservation to a problem.
Wrong move:
Forgetting momentum is a vector, so direction and sign matter.
Why:
Ignoring direction leads to incorrect cancellation or addition of momentum components.
Correct move:
Set a coordinate system and track the sign of all momentum components before solving.
3. Quick Reference Cheatsheet
Concept | Key Formula/Rule |
|---|---|
Linear momentum | |
Impulse | |
Impulse-Momentum Theorem | |
Conservation of momentum (isolated system) | |
Elastic collision condition | |
2D momentum conservation | |
Total system momentum |
What's Next
Begin your study of this unit with the first sub-topic below to get started. After completing all sub-topics in this momentum unit, you will progress to the next unit on energy, another core conservation law that is frequently paired with momentum to solve complex multi-step AP Physics 1 problems.