Detailed Study Notes on Kinematics and Kinetics

KINEMATICS AND KINETICS

Garcia HES 346

Lecture Outline

• Kinematics
  1. Types of motion
  2. Osteokinematics vs Arthrokinematics
  3. Position
  4. Distance vs Displacement
  5. Speed vs Velocity
  6. Acceleration
• Kinetics
  1. Mass vs Weight
  2. Inertia
  3. Force
  4. Torque
  5. Pressure
  6. Volume vs Density
  7. Work vs Power

Mechanics

• Dynamics
• Statically
• Kinetics
  • Linear or Angular
• Kinematics
  • Linear or Angular
• Arthrokinematics
• Osteokinematics

KINEMATICS

Garcia HES 346

Types of Motion

• Linear Motion (AKA Translation)
  • Rectilinear: Movement in a straight line.
  • Curvilinear: Movement along a curved path.
• Angular Motion (AKA Rotation)
• General Motion: Combination of linear and angular motion.
• Relative Motion: Motion of an object as observed from a particular reference point.

Osteokinematics vs Arthrokinematics

• Osteokinematics:
  • Refers to the movement of bones relative to the three planes of movement (sagittal, frontal, transverse).
  • Examples of joint motions.
• Arthrokinematics:
  • Refers to the movement of joint surfaces (between the bones).
  • Movements include rolls, glides, and spins.

Position

• Definition: A location in space, which requires a reference point.
• Coordinate System: A framework for identifying positions in space.
• Body Position: Defined by anatomical reference positions and directional terms.
  • Planes: Sagittal, frontal, transverse.
  • Axes: Vertical, horizontal, and lateral axes.

Common Quantities in Kinematics

1. Distance and Displacement
2. Speed and Velocity
3. Acceleration

Distance and Displacement

• Distance:
  • A measure of the path length along the motion path.
  • Unit of measurement: centimeter (cm), meter (m), or kilometer (km).
  • Conversion: 1 in = 2.54 cm
• Displacement:
  • A measure of the straight line from the initial to the final position, indicating the change in position and specifying the direction traveled.
  • Linear or Angular Measurement is applicable.

Speed and Velocity

• Speed Formula:
  $ext{Speed} = \frac{ ext{Distance}}{ ext{Time}}$
• Velocity Formula:
  • $ext{Velocity} = \frac{ ext{Displacement}}{ ext{Time}}$
  • Or,
    $ext{Velocity} = \frac{ ext{Change in Position}}{ ext{Change in Time}}$
• Calculating Velocity:
  • $ext{Velocity} = \frac{ ext{Position}<em>2 - ext{Position}</em>1}{ ext{Time}<em>2 - ext{Time}</em>1}$
• SI Units for Measurement:
  • meters/second (m/s) for linear motion, and degrees/second (°/s) for angular motion.

Average Speed

• Formula:
  $ext{Average Speed} = \frac{ ext{Distance}}{ ext{Time Taken}}$

Application of Speed in Sports

• Example from 2009 IAAF World Championship 100 m dash
  • Usain Bolt: 9.58 seconds
  • Tyson Gay: 9.71 seconds
  • Average Speed Calculations:
    • Bolt:
      $ext{Average Speed} = \frac{100 ext{m}}{9.58 ext{sec}} = 10.44 ext{m/s}$
    • Gay:
      $ext{Average Speed} = \frac{100 ext{m}}{9.71 ext{sec}} = 10.30 ext{m/s}$

Analyzing Speeds

• Speed during the first and last 50 m:
  • First 50 m:
    • Bolt: 5.47 seconds
    • Gay: 5.55 seconds
  • Second 50 m:
    • Bolt: 4.11 seconds
    • Gay: 4.16 seconds
  • Calculation of Speeds:
    • For the first 50 m (Bolt):
      $ext{Speed} = \frac{50 ext{m}}{5.47 ext{sec}} = 9.14 ext{m/s}$
    • For the first 50 m (Gay):
      $ext{Speed} = \frac{50 ext{m}}{5.55 ext{sec}} = 9.01 ext{m/s}$
    • For the second 50 m (Bolt):
      $ext{Speed} = \frac{50 ext{m}}{4.11 ext{sec}} = 12.17 ext{m/s}$
    • For the second 50 m (Gay):
      $ext{Speed} = \frac{50 ext{m}}{4.16 ext{sec}} = 12.02 ext{m/s}$

Acceleration

• Law of Acceleration (Newton’s Second Law of Motion):
  • Acceleration occurs when forces act on a mass.
  • Definition of Acceleration:
    • Rate of change of velocity.
    • Formula:
      $ext{Acceleration} = \frac{ ext{Change in Velocity}}{ ext{Change in Time}}$
    • Another form:
      $ext{Acceleration} = \frac{ ext{Velocity}<em>{ ext{final}} - ext{Velocity}</em>{ ext{initial}}}{ ext{Change in Time}}$
  • Significance of Sign:
    • Can be positive or negative.
  • SI Unit of Measurement:
    • meters/second squared (m/s²) for both linear and angular acceleration.

Observations of Acceleration

1. Speeding up: Indicates positive acceleration.
2. Slowing down: Indicates negative acceleration.
3. Changing directions: Indicates acceleration even with constant speed.

Mini Check Questions

1. Type of Motion Examples:
   • Ball thrown from outfield to first base.
   • Car moving on a straight road.
2. Identifying Speed vs Velocity:
   • 10 min/mile pace: Speed
   • 10 min/mile going west: Velocity
3. Distance and Displacement in a Marathon Loop:
4. Is Acceleration Present?
   • Car turning the corner at a constant speed.

KINETICS

Garcia HES 346

Linear and Angular Kinetics

• Force in Linear Kinetics
• Torque in Angular Kinetics

Important Terms in Kinetics

• Kinetic Chain:
  • A system of segments subject to forces; could be body or limb.
• Mass and Weight:
  • Mass: Amount of matter in an object.
  • Weight: Gravitational force exerted on a body, defined as:
    $ext{Weight} = ext{Mass} imes ext{Acceleration of Gravity} ext{ (where } g = -9.81 ext{ m/s}^2)$
  • SI Units:
    • Mass: kilogram (kg) (1 kg = 2.2 lbs)
    • Weight: Newton (N) (1 lb = 4.45 N; 1 kg = 9.8 N)
• Center of Mass:
  • The point at the exact center of an object's mass.

Inertia

• Definition:
  • Resistance to action or change; resistance to acceleration.
• Characteristics:
  • Force that resists an object's change in movement status.
  • Has no units; can be referenced as proportional to its mass.
  • More mass results in the tendency to maintain the current state of motion.
• Law of Inertia (Newton’s First Law):
  • An object at rest remains at rest and an object in motion remains in motion unless acted upon by an external force.

Force

• Definition:
  • A push or pull that changes or tends to change the state of rest or motion of matter.
• Formula:
  $ext{Force} = ext{Mass} imes ext{Acceleration}$
• SI Unit:
  • Newton (N), (pounds are also common).
• Newton’s Third Law of Motion:
  • For every action, there is an equal and opposite reaction.

Characteristics of Force

1. Point of application.
2. Line of application.
3. Direction (push or pull).
4. Magnitude.

Types of Forces

1. Gravitational Force:
   • The most common force; mutual attraction between two objects; proportional to mass.
2. Reaction Force:
   • Acts when two objects are in contact, notably ground and joint reaction forces.
3. Frictional Force:
   • Contact forces that act between and parallel to two surfaces in contact; can be dry or fluid friction.
4. Muscular Force:
   • Generated by muscles that move bones, changing the shape of the system.
5. Inertial Force:
6. Elastic Force:
   • Elasticity is the ability to return to normal shape after deformation; amount of deformation is proportional to force.

Torque

• Definition:
  • A rotating or turning force that occurs when an object rotates around an axis.
• Formula:
  $ext{Torque} = ext{Force} imes ext{Moment Arm Length}$
• Moment Arm Length:
  • The perpendicular distance between the axis of rotation and the point where force is applied.
• Can be internal or external.

Pressure

• Definition:
  • Result of contact force.
• Formula:
  $ext{Pressure} = \frac{ ext{Force}}{ ext{Area}}$
• SI Unit:
  • Newton/cm² or Pascals (Pa).
• Application:
  • Related to preventing pressure ulcers.

Volume and Density

• Volume:
  • Amount of three-dimensional space occupied by a body.
  • SI Unit: cm³
• Density:
  • Defined as:
    $ext{Density} = \frac{ ext{Mass}}{ ext{Volume}}$
  • SI Unit: kg/m³

Work and Power

• Work:
  • Defined as the force that causes the displacement of an object.
  • Formula:
    $ext{Work} = ext{Force} imes ext{Displacement}$
  • Work can be positive or negative.
  • Unit: Newton-meter (N·m) or Joule (J).
• Power:
  • Defined as the rate of work performed.
  • Formula:
    $ext{Power} = \frac{ ext{Work}}{ ext{Time}}$
  • SI Unit: Watt (W).

Mini Check Activities

• Identify the forces illustrated in relevant pictures (not provided in the transcript).

References

• Source: Biomechanics of Human Motion: Basics and Beyond for the Health Professions, edited by Barney LeVeau, SLACK, Incorporated, 2010. ProQuest Ebook Central.