College Board-Aligned Original Notes

AP Physics 1: Algebra-Based Unit 4 Topic 4: Elastic and inelastic collisions

Collisions are analyzed with momentum conservation and classified by what happens to kinetic energy.

Unit 4: Linear Momentum. College Board exam weighting listed for this unit: 10%-15% of multiple-choice exam score.

What to Know

Momentum is conserved for an isolated collision system.
Kinetic energy is conserved in an elastic collision but not in an inelastic collision.
In a perfectly inelastic collision, objects stick together after impact.
Always connect this topic back to the larger unit: Linear Momentum.

Detailed Notes

Elastic and inelastic collisions belongs to Unit 4: Linear Momentum. Collisions are analyzed with momentum conservation and classified by what happens to kinetic energy. Start by naming the system, choosing axes or a sign convention when needed, and identifying which physical quantity is changing.

Key relationships: Momentum is conserved for an isolated collision system. Kinetic energy is conserved in an elastic collision but not in an inelastic collision. In a perfectly inelastic collision, objects stick together after impact.

Model to use: Compare before-and-after momentum and kinetic energy tables for two colliding objects. A strong model should include labels, directions, units, and the reason each relationship applies.

AP-style move: Do not assume kinetic energy is conserved unless the collision is identified as elastic or the data support it. For free-response work, write the principle first, show the setup, and then interpret the result in the physical context.

Key Vocabulary

Elastic collision

A collision in which total kinetic energy is conserved.

Inelastic collision

A collision in which total kinetic energy is not conserved.

Perfectly inelastic collision

A collision in which objects stick together after impact.

Kinetic energy loss

Mechanical energy transformed into other forms during an inelastic collision.

Collision system

The group of objects included in the momentum analysis.

Quick Practice

How would you explain Elastic and inelastic collisions in one or two AP-style sentences?

Name the concept, apply it to a specific example or source, and explain the reasoning that connects the evidence to your answer.

Official Alignment

Reference and Attribution

AP Physics 1 concept reference: AP Physics 1: Concise Summary Notes by IITian Academy. EduCompanion used this source as a topic checklist and conceptual reference, then rewrote the study notes in original wording.

AP Physics 1: Concise Summary Notes