# 2: Interactions

Activities & Reader (ISBN 0-7872-3929-1, 224 pages)

How to Use this Book *xi*

Acknowledgments *xiii*

### Activities

- 36 - Introducing Vectors
*137* - 37 - Representing Vectors Using Components
*145* - 38 - Changing Vector Representations
*149* - 39 - Adding Vectors
*155* - 40 - Finding Changes in Vector Quantities
*161* - 41 - Recognizing Interactions
*165* - 42 - Identifying Interactions
*169* - 43 - Interpreting Measurements of Forces
*173* - 44 - More Interpreting Measurements of Forces
*179* - 45 - Recognizing Forces in Realistic Situations
*185* - 46 - Comparing Magnitudes of Forces
*191* - 47 - More Comparing Magnitudes of Forces
*195* - 48 - Understanding Friction Forces
*199* - 49 - Calculating Forces Using Empirical Laws
*205* - 50 - Recognizing and Interpreting Free-Body Diagrams
*209* - 51 - Drawing and Using Free-Body Diagrams
*215* - 52 - Analyzing Physical Situations Using Free-Body Diagrams
*223* - 53 - Describing Physical Situations Using Free-Body Diagrams
*227* - 54 - Summarizing and Structuring Interactions
*233* - 55 - Analyzing Physical Situations Using Newton's First and Second Laws
*235* - 56 - More Analyzing Physical Situations Using Newton's First and Second Laws
*243* - 57 - Relating the Forces Exerted on an Object to its Motion
*247* - 58 - Making Distinctions Between Newton's Second and Third Laws
*251* - 59 - Reasoning with Newton's Laws
*257* - 60 - More Reasoning with Newton's Laws
*261* - 61 - Using Newton's Laws to Determine the Magnitudes and Directions of Forces
*267* - 62 - Solving Problems with Newton's Laws
*273* - 63 - Analyzing Forces without Empirical Laws
*277* - 64 - Calculating the Values of Physical Parameters and Quantities
*281* - 65 - Labeling Parts of Solutions and Executing Solution Plans
*285* - 66 - Developing Solution Plans and Solving Force Problems
*293* - 67 - Solving Force Problems: Reflection and Integration
*297* - 68 - Summarizing and Structuring Dynamics
*301* - 69 - Going Beyond Newton's Laws
*303* - 70 - Looking for New Principles
*307*

### Reader: Chapter 2 — Describing Interactions

- 2.0 Introduction
*R37*- What is meant by
*dynamics*?*R37* - Why is acceleration such an important concept?
*R37*

- What is meant by
- 2.1 INTERACTIONS AND FORCES
*R37-46*- Interactions
*R37*- how to tell when two objects are interacting
*R37* - What if the effect is not visible?
*R37*

- how to tell when two objects are interacting
- Forces
*R37,38*- relationship between interactions and forces
*R37* - many different ways to say that two objects are interacting
*R38* - how a force might change during a time interval
*R38*

- relationship between interactions and forces
- Measuring forces
*R38*- explaining why springs are preferred for measuring forces
*R38* - importance of knowing what a scale is actually measuring
*R38*

- explaining why springs are preferred for measuring forces
- Units of force
*R38*- introducing the pound (lb) and the newton (N)
*R38* - converting from one unit of force to another
*R38*

- introducing the pound (lb) and the newton (N)
- Identifying forces
*R39-41*- identifying the objects interacting
*R39* - identifying the type of interaction
*R39,40* - determining the direction of a force
*R40,41*

- identifying the objects interacting
- Empirical force laws
*R41,42*- What is meant by an
*empirical force law*?*R41* - features common to all empirical laws
*R41* - Table I: Summary of the empirical laws for common forces
*R42* - role of magnitude vs. direction in the empirical laws
*R42*

- What is meant by an
- Fundamental laws for forces vs. empirical laws
*R42,43*- What is meant by a fundamental force law?
*R42* - the process of determining empirical force laws
*R42,43* - limitations of empirical laws
*R43*

- What is meant by a fundamental force law?
- Fundamental laws for forces
*R43*- the fundamental forces covered in this course
*R43* - Table II: Summary of the fundamental laws for two common forces
*R43*

- the fundamental forces covered in this course
- Free-body diagrams: A way to help us inventory forces
*R44,45*- the thinking behind a free-body diagram
*R44* - some valid free-body diagrams
*R44* - features of a free-body diagram
*R44,45* - optional features of a free-body diagram
*R45* - guidelines for drawing a free-body diagram
*R45*

- the thinking behind a free-body diagram
- The net force
*R46*- definition of
*net force**R46*

- definition of

- Interactions
- 2.2 NEWTON'S LAWS OF MOTION
*R47-52*- Mass vs. weight
*R47,48*- definition of
*weight**R47* - how to measure the weight of something
*R47* - definition of
*mass**R47* - how to measure the mass of something
*R47* - comparing the mass and the weight on the earth versus on the moon
*R47,48* *gravitational mass*versus*inertial mass**R48*

- definition of
- Newton's three laws of motion
*R48-50*- Newton's first law of motion
*R48*- verbal statement of Newton's 1st law
*R48* - definition of
*net force**R48*

- verbal statement of Newton's 1st law
- Newton's second law of motion
*R49*- verbal statement of Newton's 1st law
*R49* - mathematical statement of Newton's 1st law
*R49* - definitions of
*inertial mass*and*gravitational mass**R49* - definition of
*equilibrium**R49*

- verbal statement of Newton's 1st law
- Newton's third law of motion
*R50*- verbal statement of Newton's 3rd law
*R50* - mathematical statement of Newton's 3rd law
*R50* - relationship between forces and interactions
*R50* - explanation of the terms
*action*and*reaction**R50* - difference between a
*reaction*force and a*balancing*force*R50*

- verbal statement of Newton's 3rd law

- Newton's first law of motion
- Newton's laws and reference frames
*R50,51*- confirming Newton's laws using a constant-velocity frame
*R50* - contradicting Newton's laws using an accelerating frame
*R50* - definition of
*inertial frame**R51*

- confirming Newton's laws using a constant-velocity frame
- Newton's laws and free-body diagrams
*R51,52*- Newton's 2nd law in component form
*R51* - applying the definition of the net force using components
*R52*

- Newton's 2nd law in component form

- Mass vs. weight
- 2.3 DYNAMICS
*R52-60*- An agenda for dynamics
*R52,53* - Kinematics versus dynamics
*R53* - Reasoning with Newton's laws
*R53-56*- equilibrium situations (net force is zero)
*R54,55* - non-equilibrium situations (net force is not zero)
*R56*

- equilibrium situations (net force is zero)
- Solving problems with Newton's laws
*R56-59*- goal of this approach to learning physics
*R56* - importance of analysis and reasoning skills
*R56* - role of analysis and reasoning while problem solving
*R56-58* - overview of problem solving in physics
*R59* - diagrammatic representation of the problem-solving process
*R59* - meaning of the diagrammatic representation
*R59*

- goal of this approach to learning physics
- Summary
*R59* - Limitations of dynamics
*R59,60*- conditions needed to solve dynamics problems
*R59* - some situations in which the motion cannot be determined using dynamics alone
*R60*

- conditions needed to solve dynamics problems
- Conclusion
*R60*

- An agenda for dynamics

### Appendix: Table of Common Forces

- Contact Forces
*A1-4*- Normal force
*A1* - Tension force
*A1* - Spring force (also called Elastic force)
*A2* - Buoyant force
*A2* - Friction forces
*A3*- kinetic
*A3* - static
*A3*

- kinetic
- Air resistance force (also called Drag force)
*A4*

- Normal force
- Action-at-a-distance Forces
*A5,6*- Gravitational force
*A5*- near the surface of the Earth
*A5* - Universal Law of Gravitation
*A5*

- near the surface of the Earth
- Electrostatic force
*A6* - Magnetic force
*A6*

- Gravitational force

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