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
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
- 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
- Measuring forces R38
  - explaining why springs are preferred for measuring forces R38
  - importance of knowing what a scale is actually measuring R38
- Units of force R38
  - introducing the pound (lb) and the newton (N) R38
  - converting from one unit of force to another R38
- Identifying forces R39-41
  - identifying the objects interacting R39
  - identifying the type of interaction R39,40
  - determining the direction of a force R40,41
- 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
- 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
- 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
- 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 net force R46
  - definition of net force R46
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
- 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
  - 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
  - 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
- 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
- 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
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
- 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
- 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
- Conclusion R60

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
- Air resistance force (also called Drag force) A4
Action-at-a-distance Forces A5,6
- Gravitational force A5
  - near the surface of the Earth A5
  - Universal Law of Gravitation A5
- Electrostatic force A6
- Magnetic force A6