### Unit 9: Angular Momentum

Why do tornadoes spin so rapidly? The answer is that the air masses that produce tornadoes are themselves rotating, and when the radii of the air masses decrease, their rate of rotation increases. An ice skater increases her spin in an exactly analogous way. The skater starts her rotation with outstretched limbs and increases her spin by pulling them in toward her body. The same physics describes the spin of a skater and the wrenching force of a tornado. Clearly, force, energy, and power are associated with rotational motion. These and other aspects of rotational motion are covered in this unit. We will see that all important aspects of rotational motion either have already been defined for linear motion or have exact analogs in linear motion.

**Completing this unit should take you approximately 16 hours.**

### 9.1: Kinematics of Rotational Motion

Watch this lecture, pausing to take notes, before moving on to the reading below.

Read sections 10.1 and 10.2 of "Chapter 10: Rotational Motion and Angular Momentum" (pages 317 to 326). Look over the corresponding conceptual questions on page 348 to test your understanding of the sections.

Try solving these practice problems.

Scroll down the page to "Ch 9: Rotational Motion," and select the link to open the PDF document. Read the entirety of Chapter 9. From pages 9-4 to 9-10, solve problems 1-4, 10-13, 16, and 21.

### 9.2: Dynamics of Rotational Motion

Read sections 10.3 and 10.4 of "Chapter 10: Rotational Motion and Angular Momentum" (pages 326 to 336). Look over the corresponding conceptual questions on page 349 to test your understanding of the sections.

Try solving these practice problems.

Work on solving problems 3 from SAC103 and 1, 2, and 3 from SAC123. The solutions are available, but make a serious attempt to solve the problems before looking at the solutions.

### 9.3: Conservation of Angular Momentum

Read section 10.5 of "Chapter 10: Rotational Motion and Angular Momentum" (pages 336 to 341). Look over the corresponding conceptual questions on pages 349-351 to test your understanding of the sections.

Try solving these practice problems.

Follow this animation through the various steps until you can convincingly explain what a cat does to land on its feet to a non-physics student.

Work on solving problems 1 through 4 from SAC105. The solutions are available, but make a serious attempt to solve the problems before looking at the solutions.

### Unit 9 Assessment

Please take this assessment to check your understanding of the materials presented in this unit.

**Notes:****There is no minimum required score to pass this assessment, and your score on this assessment**__will not__factor into your overall course grade.**This assessment is designed to prepare you for the Final Exam that will determine your course grade. Upon submission of your assessment you will be provided with the correct answers and/or other feedback meant to help in your understanding of the topics being assessed.****You may attempt this assessment as many times as needed, whenever you would like.**