Choose a system and model
Decide when impulse or momentum conservation explains an interaction.
AP Physics 1 · Unit 4 · Linear Momentum
Unit 4 Concept Review
Choose and test momentum models in new situations, using impulse, collisions, center of mass, and energy evidence.
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Learn by doing
Three ways to check your understanding
Use the evidence
Connect force–time area, signed momenta, and center-of-mass motion with the simulated results.
Design, test, and revise
Choose a launch that leaves two joining carts at rest, then explain the result.
The big idea
Connect the ideas before choosing a model.
Impulse changes system momentum
Jnet = ΔP. Use the area under the net-force–time curve, keeping the force direction.
Momentum and energy answer different questions
Negligible external impulse preserves total momentum. Kinetic energy is also conserved in an ideal elastic collision; other interactions can transfer it to internal energy.
Center of mass describes the whole system
Px = MvCM,x. Internal forces can rearrange the parts while the system’s center of mass continues at constant velocity.
A useful strategy
Two differently loaded carts approach and join. What should you compare before choosing their launch velocities?
Choose both carts as the system. Make their signed initial momenta add to zero.
Teaching this topic?Classroom fit, AP connections, and support
- Classroom fit
- Use after the unit for independent review, partner discussion, or a projected check of student reasoning.
- Before students begin
- Momentum and impulse, system boundaries, center of mass, and kinetic and spring potential energy. Optional help is available beside the questions.
- Built-in support
- Prepared scenes, guided prompts, and feedback on lesson questions.
- AP Physics 1 connections
- AP Physics 1 Unit 4: momentum, impulse, conservation, and elastic/inelastic collisions; center-of-mass position connects to Unit 2.
- Check for understanding
- Ask why joined carts can stop with zero final momentum even though their initial kinetic energy was positive.
Ready to put the ideas together?
The first scene is set up. Start the lesson and explore.