# 23. Static Equilibrium

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## Learning Objectives

• Be able to determine the conditions under which a rigid body is in static equilibrium.
• Be able to calculate the magnitude and direction of the torque about any point due to any force using vector decomposition and the cross product.
• Be able to calculate the magnitude of the torque about any point due to any force using the lever-arm for the perpendicular distance or the perpendicular component of the force.
• Analyze a rigid-body statics situation using a systematic methodology. Be able to:
• choose a co-ordinate system based on the specific situation in the problem;
• determine the net force and net torque about a suitable point on a rigid body;
• apply the conditions of static equilibrium to determine conditions that the forces must satisfy.

## Preparation

### Course Notes

Chapter 11.1-11.3. Young, Hugh D., Roger A. Freedman, and A. Lewis Ford. Sears and Zemansky's University Physics: with Modern Physics. 12th ed. San Francisco, CA: Addison-Wesley, 2007. ISBN: 9780805321876.

## Lecture Video

### Video Excerpts

Watch the following excerpts from the Physics I lecture videos:

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## Learning Activities

### Guided Activities

Read through the class slides carefully. They explain all of the concepts from the module.

### Self-Assessment

Do the Concept Questions first to make sure you understand the main concepts from this module. Then, when you are ready, try the Challenge Problems. If you are struggling with the Challenge Problems, watch the Homework Help Session videos, which will give you tips on how to tackle problems of this type.

### Concept Questions

Concept Questions (PDF)

Solutions (PDF)

### Challenge Problems

Challenge Problems (PDF)

Solutions (PDF)

## Problem Solving Help

In the following videos Prof. Walter Lewin explains how to approach the Challenge Problems.

### Help Session 1

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» iTunes U (MP4 - 28MB)
» Internet Archive (MP4 - 28MB)

### Help Session 2

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» iTunes U (MP4 - 35MB)
» Internet Archive (MP4 - 35MB)

## Related Resources

There are countless resources available online to help you learn physics. Try these:

• Read about equilibrium from Dr. Doug Davis at Eastern Illinois University:
• Read the Physics material on Connexions:

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