Angular Momentum and Angular Impulse

Ethan Williams
9 min read
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Study Guide Overview
This study guide covers angular momentum and angular impulse in AP Physics C: Mechanics. It explains how to calculate angular momentum for both rotating objects and particles, defines angular impulse and its relationship to torque, and details the impulse-momentum theorem for rotation. The guide also includes interpreting graphs of torque vs. time and angular momentum vs. time, and provides practice questions with solutions and exam tips.
#AP Physics C: Mechanics - Angular Momentum & Impulse Study Guide 🚀
Hey there, future physics pro! Let's break down angular momentum and impulse. This guide is designed to make sure you're feeling confident and ready to ace the exam. No stress, just clear explanations and smart strategies. Let's get started!
#1. Angular Momentum: The Spin Master 🌀
#1.1. Understanding Angular Momentum
Angular momentum is all about an object's tendency to keep rotating. It's like the rotational version of linear momentum. Think of a spinning figure skater – they keep spinning because of their angular momentum!
Angular momentum is a vector quantity. This means it has both magnitude and direction. The direction of the angular momentum vector is perpendicular to the plane of rotation and is determined by the right-hand rule.
#1.2. Calculating Angular Momentum
#1.2.1. Magnitude of Angular Momentum
For a rigid object rotating about a fixed axis, we use:
- : Angular momentum (kg·m²/s)
- : Moment of inertia (kg·m²), which is the resistance to rotational motion
- : Angular velocity (rad/s), which is how fast something is spinning
Remember L = I love ω! (Think of a heart ❤️ for love, and imagine it spinning!)
#1.2.2. Angular Momentum About a Point
For an object moving in a curved path or a particle, we use the cross product:
- : Angular momentum vector
- : Position vector from the reference point to the object
- : Linear momentum vector ()
The direction of is perpendicular to both and , following the right-hand rule.

Right-hand rule for angular momentum: Point your fingers along , curl them towards , and your thumb points in the direction of .
#1.2.3. Key Considerations
- The choice of rotation axis is crucial! It affects the value of angular momentum.
- An object moving in a straight line can have angular momentum relative to a point that is not on its line of motion.
- Angular momentum depe...

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