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Introduction to Exercise Science for Fitness Professionals: Inertia and Momentum

Introduction to Exercise Science for Fitness Professionals
Inertia and Momentum
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table of contents
  1. Cover
  2. Title Page
  3. Copyright
  4. Table Of Contents
  5. Attribution and OER Revision Statement
  6. Chapter 1: Body Systems Review
    1. The Cardiovascular System
    2. The Nervous System
    3. Reflexes
    4. The Skeletal System
    5. Divisions of the Skeletal System
    6. Skeletal Muscle
    7. Divisions of the Skeletal Muscles
    8. Describing Motion and Movements
    9. Identify Anatomical Locations
  7. Chapter 2: Biomechanics and Human Movement
    1. The Basics of Biomechanics
    2. Inertia and Momentum
    3. Force
    4. Doing Work
    5. Body Levers
    6. Nervous System Control of Muscle Tension
    7. Muscle Tissue and Motion
  8. Chapter 3: Exercise Metabolism
    1. Introduction to Bioenergetics and Metabolism
    2. Overview of Metabolic Reactions
    3. Metabolic States of the Body
    4. The Cardiorespiratory System and Energy Production
    5. ATP in Living Systems
    6. Types of Muscle Fibers
    7. Exercise and Muscle Performance
    8. Nutrition, Performance, and Recovery
    9. Carbohydrate Metabolism
    10. Protein Metabolism
    11. Lipid Metabolism
  9. Chapter 4: Fitness Principles
    1. What are Physical Activity and Exercise?
    2. The Physical Activity Guidelines for Americans
    3. Components of Health-Related Fitness
    4. Principles of Adaptation and Stress
    5. FITT Principle
    6. Rest, Recovery, and Periodization
    7. Reversibility
    8. Training Volume
    9. Individual Differences
    10. Creating a Successful Fitness Plan
    11. Additional Safety Concerns
    12. Test Your Knowledge
  10. Chapter 5: Flexibility Training Principles
    1. What is Flexibility?
    2. Benefits of Flexibility and Stretching
    3. Improving Range of Motion
    4. Improving Flexibility
    5. Creating an Effective Stretching Program
    6. Assessing Your Flexibility
    7. Test Your Knowledge
  11. Chapter 6: Cardiorespiratory Training Principles
    1. What are the Cardiovascular and Respiratory Systems?
    2. Introduction: The Cardiovascular System
    3. Introduction: The Respiratory System
    4. The Process of Breathing and Respiratory Function
    5. Modifications to Breathing
    6. Changes in the CR System
    7. Measuring Heart Rate
    8. Measuring Intensity
    9. Cardiorespiratory Fitness Assessment
    10. Test Your Knowledge
  12. Chapter 7: Core and Balance Training Principles
    1. Lumbar Spine
    2. Abdomen
    3. The Pelvic Girdle
    4. Creating Movement at the Hip
    5. Balance
    6. Center of Gravity
    7. Supporting the Body
    8. Friction in Joints
    9. Human Stability
    10. Guidelines for Core and Balance Training
  13. Chapter 8: Plyometrics, Speed, Agility, and Quickness Training Principles
    1. Plyometric Exercises
    2. Variables of Plyometric Training
    3. Progressing a Plyometric Program
    4. Speed, Agility, and Quickness
    5. Speed
    6. Agility
    7. Quickness
  14. Chapter 9: Resistance Training Principles
    1. Resistance Exercise Programming
    2. Exercise Order
    3. Types of Resistance Training
    4. Basics of Form during Resistance Training
    5. Resistance Training Systems
    6. Resistance Training Conclusion
    7. Test Your Knowledge
  15. References
  16. Glossary
  17. MARC Record

11

Inertia and Momentum

Julio Gea-Benacloche

Inertia2

In everyday language, we speak of something or someone “having a large inertia” to mean, essentially, that they are very difficult to set in motion. This usage of the word “inertia” is consistent with the “law of inertia” which states, among other things, that an object at rest, if left to itself, will just remain at rest, but it goes a bit beyond that by trying to quantify just how hard it may be to get the object to move.

We do know, from experience, that lighter objects are easier to set in motion than heavier objects, but most of us probably have an intuition that gravity (the force that pulls an object towards the earth and hence determines its weight) is not involved in an essential way here. Imagine, for instance, the difference between slapping a volleyball and a bowling ball. It is not hard to believe that the latter would hurt as much if we did it while floating in free fall in the space station (in a state of effective “weightlessness”) as if we did it right here on the surface of the earth. In other words, it is not (necessarily) how heavy something feels, but just how massive it is.

Momentum2

For an object of (inertial) mass m moving, in one dimension, with velocity v, we define its momentum as

p = mv

(the choice of the letter p for momentum is apparently related to the Latin word “impetus”).

We can think of momentum as a sort of extension of the concept of inertia, from an object at rest to an object in motion. When we speak of an object’s inertia, we typically think about what it may take to get it moving; when we speak of its momentum, we typically think of that it may take to stop it (or perhaps deflect it). So, both the inertial mass m and the velocity v are involved in the definition.

We may also observe that what looks like inertia in some reference frame may look like momentum in another. For instance, if you are driving in a car towing a trailer behind you, the trailer has only a large amount of inertia, but no momentum, relative to you, because its velocity relative to you is zero; however, the trailer definitely has a large amount of momentum (by virtue of both its inertial mass and its velocity) relative to somebody standing by the side of the road.


Gea-Banacloche, J. (2019). University Physics I: Classical Mechanics. Open Educational Resources. Retrieved from https://scholarworks.uark.edu/oer/3

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Copyright © 2021

                                by Amanda Shelton

            Introduction to Exercise Science for Fitness Professionals by Amanda Shelton is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.
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