Chapter 3 Biomechanics Concepts I

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Chapter 3 Biomechanics Concepts I

• Biomechanics Study of biological systems by
  means of mechanical principles
• Sir Isaac Newton, father of Mechanics

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Basic types of Motion

• Linear
• rectilinear
• curvilinear
• Angular or rotational
• Combined or general

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Human Analysis

• Internal mechanical factors creating and
  controlling movement inside the body
• External factors affecting motion from outside
  the body

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Kinematics

• Describes motion
• Time
• Position
• Displacement
• Velocity
• Acceleration
• Vectors
• Angular and linear quantities

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Kinematics Formulas
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Kinetics

• Explains causes of motion
• Mass
• amount of matter (kg)
• Inertia resistance to being moved
• Moment of Inertia (rotation) I mr2

Axis
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Kinetics

• Force push or pull that tends to produce
  acceleration
• Important factor in injuries
• Vector

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Kinetics

• Idealized force vector
• Force couple system

F
F
F
MFd
d
d


F
F
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Kinetics Force

• Force Injury factors
• Magnitude
• Location
• Direction
• Duration
• Frequency
• Variability
• Rate

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Kinetics Force System

• Linear
• Parallel
• Concurrent
• General
• Force Couple

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Center of Mass or Gravity

• Imaginary point where all the mass of the body or
  system is concentrated
• Point where the bodys mass is equally distributed

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Pressure

• P F/A
• Units (Pa N m2)
• In the human body also called stress
• Important predisposing factor for injuries

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Moments of Force (Torque)

• Effect of a force that tends to cause rotation
  about an axis
• M F d (Nm)
• If F and d are ?
• Force through axis

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Moments of Force (Torque)

• Force components
• Rotation
• Stabilizing or destabilizing component

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Moments of Force (Torque)

• Net Joint Moment
• Sum of the moments acting about an axis
• Human represent the muscular activity at a joint
• Concentric action
• Eccentric action
• Isometric

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Moments of Force (Torque)

• Large moments tends to produce injuries on the
  musculo-skeletal system
• Structural deviation leads to different MAs

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1st Law of Motion

• A body a rest or in a uniform (linear or angular)
  motion will tend to remain at rest or in motion
  unless acted by an external force or torque
• Whiplash injuries

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2nd Law of Motion

• A force or torque acting on a body will produce
  an acceleration proportional to the force or
  torque
• F m a or T I ?

F
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3rd Law of Motion

• For every action there is an equal and opposite
  reaction (torque and/or force)
• Contact forces GRF, other players etc.

GRF
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Equilibrium

• Sum of forces and the sum of moments must equal
  zero
• ? F 0
• ? M 0
• Dynamic Equilibrium
• Must follow equations of motions
• ? F m x a
• ? T I x ?

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Work Power

• Mechanical Work
• W F d (Joules)
• W F dcos (?)
• Power rate of work
• P W/??t (Watts)
• P F v
• P F (d/t)

d
W
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Mechanical Energy

• Capacity or ability to do work
• Accounts for most severe injuries
• Classified into
• Kinetic (motion)
• Potential (position or deformation)

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Kinetic Energy

• Bodys motion
• Linear or Angular
• KE.5mv2
• KE?.5 I?2

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Potential Energy

• Gravitational potential to perform work due to
  the height of the body
• Ep mgh
• Strain energy stored due to deformation
• Es .5kx2

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Total Mechanical Energy

• Body segments rigid (nodeformable), no strain
  energy in the system
• TME Sum of KE, KE?, PE

TME (.5m v2)(.5 I ?2)(m g h )
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Momentum
P

• Quantity of motion
• pm v (linear)
• Conservation of Momentum
• Transfer of Momentum
• Injury may result when momentum transferred
  exceeds the tolerance of the tissue
• Impulse ?Momentum

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Angular Momentum

• Quantity of angular motion
• HI ? (angular)
• Conservation of angular momentum
• Transfer of angular momentum

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Collisions

• Large impact forces due to short impact time
• Elastic deformation
• Plastic deformation (permanent change)
• Elasticity ability to return to original shape
• Elastoplastic collisions
• Some permanent deformation
• Transfer and loss of energy velocity

• Coefficient of restitution
• eRvpost/Rvpre

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Friction

• Resistance between two bodies trying to slide
• Imperfection of the surfaces
• Microscopic irregularities - asperities
• Static friction
• flt ?sN
• Kinetic
• fµkN

f
N
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Friction

• Rolling Lower that static and kinetic friction
  (100-1000 times)
• Joint Friction - minimized
• Blood vessels - atherosclerosis

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Fluid mechanics

• Branch of mechanics dealing with the properties
  and behaviors of gases fluids

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Fluid Flow

• Laminar
• Turbulent
• Effects of friction on arterial blood flow

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Fluid Forces

• Buoyancy
• Drag
• Surface
• Pressure
• Wave
• Lift
• Magnus forces
• Viscosity
• Biological tissue must have a fluid component

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Fluid Forces