Chapter 3 Biomechanics Concepts I

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# Chapter 3 Biomechanics Concepts I - PowerPoint PPT Presentation

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

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
• Internal: mechanical factors creating and controlling movement inside the body
• External: factors affecting motion from outside the body
Kinematics
• Describes motion
• Time
• Position
• Displacement
• Velocity
• Acceleration
• Vectors
• Angular and linear quantities
Kinetics
• Explains causes of motion
• Mass
• amount of matter (kg)
• Inertia: resistance to being moved
• Moment of Inertia (rotation) I = m·r2

Axis

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

d

Kinetics
• Idealized force vector
• Force couple system

F

F’

F

M=Fd

d

d

=

=

F

F

Kinetics: Force
• Force & Injury factors
• Magnitude
• Location
• Direction
• Duration
• Frequency
• Variability
• Rate
Kinetics: Force System
• Linear
• Parallel
• Concurrent
• General
• Force Couple
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
Pressure
• P = F/A
• Units (Pa = N m2)
• In the human body also called stress
• Important predisposing factor for injuries
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
Moments of Force (Torque)
• Force components
• Rotation
• Stabilizing or destabilizing component
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
Moments of Force (Torque)
• Large moments tends to produce injuries on the musculo-skeletal system
• Structural deviation leads to different MA’s
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
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

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

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 
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

Mechanical Energy
• Capacity or ability to do work
• Accounts for most severe injuries
• Classified into
• Kinetic (motion)
• Potential (position or deformation)
Kinetic Energy
• Body’s motion
• Linear or Angular
• KE=.5·m·v2
• KE=.5 ·I·2
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
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 )

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
Angular Momentum
• Quantity of angular motion
• H=I · (angular)
• Conservation of angular momentum
• Transfer of angular momentum
Large impact forces due to short impact time

Elastic deformation

Plastic deformation (permanent change)

Elastoplastic collisions

Some permanent deformation

Transfer and loss of energy & velocity

Coefficient of restitution

e=Rvpost/Rvpre

Collisions
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

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

### Fluid mechanics

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

Fluid Flow
• Laminar
• Turbulent
• Effects of friction on arterial blood flow
Fluid Forces
• Buoyancy
• Drag
• Surface
• Pressure
• Wave
• Lift
• Magnus forces
• Viscosity
• Biological tissue must have a fluid component