Download - Biomechanics concepts
BIOMECHANICS CONCEPTS
BIOMECHANICSStudy of Biological Systems by Means of Mechanical Principles
father of MechanicsSir Isaac Newton
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BIOMECHANICS
Biology
Skeletal system
Muscular system
Nervous system
Physics
Mechanics
Kinetics Kinematics
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HUMAN MOVEMENT ANALYSIS
BIOMECHANICS KINESIOLOGY
KINETICS FUNCTIONALKINEMATICS
Linear
Position Velocity
Acceleration
Position Velocity
Acceleration
Linear Angular
Force Torque
Angular
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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 Linear Motion Angular Motion
Symbol Equation Symbol Equation
Time t t=t2-t1 t t=t2-t1
Position (x,y) (r,)
Displacement d d=d2-d1
Velocity v v=d/t =/t
Acceleration a a=v/t =/t
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Kinetics Explains causes of motion
Mass amount of matter (kg)
Inertia: resistance to being moved Moment of Inertia (rotation) I = m·r2
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
d= d
FF
F
F’
=d
F
M=Fd
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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 (COm) or Gravity (COG) It is an imaginary point where
there is intersection of all 3 cardinal plane.
Imaginary point where all the mass of the body or system is concentrated
Point where the body’s 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 MA’s
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NEWTONIAN LAWS of Motion
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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 ·d·cos ()
Power: rate of work P = W/t (Watts) P = F ·v P = F ·(d/t)
dW 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
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Kinetic Energy Body’s motion Linear or Angular
KE=.5·m·v2
KE=.5 ·I·2
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Potential Energy Gravitational: potential to
perform work due to the height of the body Ep= m·g·h
Strain: energy stored due to deformation Es= .5·k·x2
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Total Mechanical Energy Body segment’s: rigid (nodeformable), no strain
energy in the system TME = Sum of KE, KE, PE
TME = (.5·m ·v2)+(.5 ·I ·2)+(m ·g ·h )
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Momentum Quantity of motion p=m ·v (linear) Conservation of Momentum Transfer of Momentum Injury may result when momentum
transferred exceeds the tolerance of the tissue
Impulse = Momentum
P
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Angular Momentum Quantity of angular
motion H=I · (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 e=Rvpost/Rvpre
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Friction Resistance between two bodies
trying to slide Imperfection of the surfaces Microscopic irregularities -
asperities Static friction
f< s·N Kinetic
f=µk·N N
f
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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 & 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
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