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Chapter 3 Biomechanics Concepts I

Chapter 3 Biomechanics Concepts I. Biomechanics: Study of biological systems by means of mechanical principles Sir Isaac Newton, father of Mechanics. Basic types of Motion. Linear rectilinear curvilinear Angular or rotational Combined or general. Human Analysis.

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Chapter 3 Biomechanics Concepts I

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  1. Chapter 3 Biomechanics Concepts I Biomechanics: Study of biological systems by means of mechanical principles Sir Isaac Newton, father of Mechanics

  2. Basic types of Motion • Linear • rectilinear • curvilinear • Angular or rotational • Combined or general

  3. Human Analysis • Internal: mechanical factors creating and controlling movement inside the body • External: factors affecting motion from outside the body

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

  5. Kinematics Formulas

  6. Kinetics • Explains causes of motion • Mass • amount of matter (kg) • Inertia: resistance to being moved • Moment of Inertia (rotation) I = m·r2 Axis

  7. Kinetics • Force: push or pull that tends to produce acceleration • Important factor in injuries • Vector

  8. d Kinetics • Idealized force vector • Force couple system F F’ F M=Fd d d = = F F

  9. Kinetics: Force • Force & Injury factors • Magnitude • Location • Direction • Duration • Frequency • Variability • Rate

  10. Kinetics: Force System • Linear • Parallel • Concurrent • General • Force Couple

  11. Center of Mass or Gravity • Imaginary point where all the mass of the body or system is concentrated • Point where the body’s mass is equally distributed

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

  13. 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

  14. Moments of Force (Torque) • Force components • Rotation • Stabilizing or destabilizing component

  15. 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

  16. Moments of Force (Torque) • Large moments tends to produce injuries on the musculo-skeletal system • Structural deviation leads to different MA’s

  17. 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

  18. 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

  19. 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

  20. 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 

  21. 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) d W

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

  23. Kinetic Energy • Body’s motion • Linear or Angular • KE=.5·m·v2 • KE=.5 ·I·2

  24. 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

  25. 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 )

  26. Momentum P • 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

  27. Angular Momentum • Quantity of angular motion • H=I · (angular) • Conservation of angular momentum • Transfer of angular momentum

  28. 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 Collisions

  29. Friction • Resistance between two bodies trying to slide • Imperfection of the surfaces • Microscopic irregularities - asperities • Static friction • f<s·N • Kinetic • f=µk·N f N

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

  31. Fluid mechanics Branch of mechanics dealing with the properties and behaviors of gases & fluids

  32. Fluid Flow • Laminar • Turbulent • Effects of friction on arterial blood flow

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

  34. Fluid Forces

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