# 7. Concept of Force

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## Learning Objectives

• Explain the concept of a force law as an empirical relation between the force exerted on an object and properties of the object.
• Be able to use Newton’s Third law when analyzing problems involving more than one object.
• Be able to construct a force diagram to represent the forces exerted on the system by other objects that interact with the system.
• Explain how empirical force laws are used in Newton’s 2nd law.
• Explain the relationship between the description of motion and Newton’s 2nd law.
• Be able to explain the meaning Newton’s 1st law: physical laws (such as force laws) are the same in all inertial reference frames.

## Preparation

### Course Notes

Notes: The Concept of Force (PDF - 5.3MB)

### Suggested Textbook Reading (Optional)

Chapter 4.1-4.6, 12.1-12.2. 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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Download the complete lectures from this course:

## Learning Activities

### Guided Activities

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

Slides: Concept of Force (PDF - 1.8MB)

### 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 - 1.4MB)

## Problem Solving Help

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

### Help Session 1

{'English - US': '/courses/physics/8-01sc-physics-i-classical-mechanics-fall-2010/force-and-newtons-laws-of-motion/concept-of-force/help-session-1/RXWhCQHqvwQ.srt'}

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### Help Session 2

{'English - US': '/courses/physics/8-01sc-physics-i-classical-mechanics-fall-2010/force-and-newtons-laws-of-motion/concept-of-force/help-session-2/q1WOstOZqsU.srt'}

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## Related Resources

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

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