What is AP Physics 1 Unit 4 about?
Unit 4 Linear Momentum is a current AP Physics 1 unit with an official multiple-choice weighting of 10–15%. This hub maps every topic in the unit to focused lessons, examples, representations and practice.
- Official unit weighting: 10–15% of the MCQ section.
- Every official topic in this unit has its own lesson and 42-MCQ/4-FRQ practice bank.
- Use the unit hub for sequencing; use the child topic pages for exact definitions and worked reasoning.
Unit 4 · Linear Momentum
Unit 4 describes interactions through momentum and impulse, especially collisions, recoil, and short-duration forces.
Unit 4 topic map
Use the unit hub to understand how the ideas connect; use each topic lesson for definitions, real examples, equations, worked reasoning, misconceptions and focused practice.
Linear Momentum
Linear momentum is a vector quantity equal to mass times velocity; it describes translational motion in a form especially useful for interactions and collisions.
Change in Momentum and Impulse
Impulse is the effect of a force acting over a time interval and equals the change in momentum of the object or system.
Conservation of Linear Momentum
Linear momentum of a system remains constant when the net external impulse on that system is zero or negligible during the interval of interest.
Elastic and Inelastic Collisions
A collision is elastic if both total momentum and total kinetic energy are conserved; it is inelastic if momentum is conserved for an isolated system but kinetic energy decreases, with a perfectly inelastic collision ending with objects stuck together.