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Biomechanics Exam 1

by: Gianna Rossi

Biomechanics Exam 1 3337

Marketplace > Temple University > Biology > 3337 > Biomechanics Exam 1
Gianna Rossi

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About this Document

Outline of basic terms, concepts, and things to keep in mind for exam.
Comparative Biomechanics
Dr. Tonia Shieh
Study Guide
Physics, Biomechanics
50 ?




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This 6 page Study Guide was uploaded by Gianna Rossi on Saturday September 24, 2016. The Study Guide belongs to 3337 at Temple University taught by Dr. Tonia Shieh in Fall 2016. Since its upload, it has received 4 views. For similar materials see Comparative Biomechanics in Biology at Temple University.


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Date Created: 09/24/16
Biomechanics  Exam  1  Study  Guide     History   • Giovanni  Borelli  is  the  father  of  biomechanics   • Marey  invented  the  chronophotographic  gun  (multiple  photos  on  a  single   frame)   • Stop-­‐Motion  Photography  invented  by  Eadweard  Muybridge  who  also   thought  of  the  zoopaxiscope  (multiple  picture  at  high  rate  to  create  a  video   like  stream)  by  betting  on  horses’  aerial  phase     Basic  Terms  to  Know:   • Extensibility   • Work  of  Extension   • Young’s  Modulus  (stiffness)  –  slope  of  a  line  in  a  stress  strain  curve,  increases   with  extension   • Stiffness   • Brittleness   • Strength   • Resilience   • Work  of  Fx   • Toughness   • Velocity:  (has  direction  and  magnitude  AKA  a  vector)   • Scalar:  (numerical,  speed)     Central  Pattern  Generator  (CPG’s)     • Bundle  of  nerves  (e.g  heart  SA  node  –  pace  maker)     Control  Mechanisms   • Proximo-­‐distal  gradient  of  control:  to  maintain  stability  you  need  to  gain   control  of  center  of  mass.  (e.g.  seen  in  the  birds  that  do  not  change  motor   patterns  while  running  on  flat  terrain  or  rough  terrain)     Physics  Principles:     Newton’s  Laws:   1. A  body  stays  at  rest  or  in  uniform  motion  in  a  straight  line  unless  a  force  is   applied  to  it.     2. Acceleration  is  proportional  to  the  applied  force  and  is  in  the  same  direction   as  the  force.     3. When  one  body  exerts  a  force  on  another,  the  second  always  exerts  a  force   that  is  equal  in  magnitude  but  opposite  in  direction.       Mass/Principle  of  Continuity:    the  rate  at  which  mass  flows  past  any  point  along  a   pipe  must  be  the  same  as  flow  past  any  point.       Momentum:  always  remains  constant  but  when  it  increases  it  is  the  reason  the  guy   standing  on  a  hose  (see  slide  from  9/2)  is  lifted  out  of  the  water.       Work  is  done  against  a  force  ONLY  when  an  object  is  moved  a  certain  distance.   Force  can  be  applied  but  work  is  only  done  when  there  is  distance.       Stress  the  amount  of  force  applied  over  a  given  area  (stress  =  F/A,  units  Pa  or  Nm )   -­‐2 it  is  omnidirectional  (in  every  given  direction)     Strain  is  a  fractional  change  in  length  or  dimensions  as  a  result  of  an  imposed   stress.  Unitless!   Formula  =  change  in  direction/  initial  (length,  area,  or  volume)     Stress  vs  Strain  curve:  as  stress  or  force  increases  as  you  strength  or  strain  a   material  where  it  suddenly  ends  is  the  point  of  fracture.  Elastic  region  is  the  region   where  the  material  is  still  fully  recoverable,  plastic  region  returns  to  a  new  point.     Ultimate  Strength:  most  stress  you  can  apply  to  a  material  before  it  breaks  entirely.   Extensibility:  ??  Work  of  Extension  ???       Moment  or  torque  forces  that  cause  rotation  review  problems  using  this!!!     Force   • Things  move  by  producing  a  force  on  the  environment  and  accelerates  in  the   opposite  direction   • Force  is  produced  by  oscillating  appendages,  so  it  is  unsteady  whereas   movement  may  be  smooth.   • Vortices  are  formed  through  movement  in  fluids  (spirals,  cyclical)   • Center  of  mass  holds  balance   • Spring  Mass  Model:  stores  energy  then  springs  up  allowing  for  movement.   Ø Propulsion  releases  stored  energy   Ø Braking  is  like  compressing  (elastic  storage  in  the   gastrocnemius  tendon)   Ø Kangaroos  have  a  pentapedal  gait;  their  energy  use  declines   the  faster  they  hop.     Jellyfish  trade-­‐off   • Good  predation  vs  good  performance   • The  larger  jellyfish  is  better  at  capturing  their  prey,  however,  they  are  weak   when  it  comes  to  speed  and  chasing  their  prey.  The  smaller  jellyfish  are   quicker  and  more  able  to  chase  their  prey  &  also  get  away  from  predators   however  due  to  their  smaller  morphology  they  are  less  likely  to  capture  their   prey.           Materials:   Characterization  of  materials:   • Isotropic:  behaves  the  same  regardless  of  the  force  applied/  loading   direction   • Anisotropic:  direction  maters  in  regards  to  its  resistance   • Tensile  materials  resist  pulling  forces  (tensile  forces)     Ø Protein  silk   Ø Collagen  (protein)   Ø Cellulose  (polysaccharide)   Ø Chitin  (polymeric  sugar)  –  insect  shells     • Pliant  Materials:  how  much  they  deform  and  how  well  they  recover  to  their   original  forms  after  removal  of  stress  (refer  to  seahorses  tail  shape)   Ø Abduction-­‐  matter  that  allows  scallops  to  open  shells   Ø Elastin_  elasticity  in  skin   Ø Resilin  -­‐  insects?   Ø Slugs  are  also  an  example  of  this.   • Rigid  Materials:  resist  stress  with  minimal  deformation.  All  are  composites,   anisotropic  (e.g.  bones  are  not  strong  when  it  comes  to  twisting)   • Flexural  stiffness-­‐  is  an  objects  resistance  to  bending  and  can  be  calculated  as   young’s  modulus  (E)  *  the  second  moment  of  area  (l).  The  further  away  the   material  lies  from  the  neutral  plate  the  more  resistance  the  object  has  or  it  is   stiffer.   • *Advantages  to  J  shaped  curve  (see  lecture  9/9)   • Euler  Buckling  –  isotropic  materials  (rarely  biological)  it  is  often  preceded   by  ovalization  and  usually  depends  on  the  restraints  at  the  end  of  the  column.   2 F = n π E I / L   • Local  Buckling  –  common  in  hollow  or  thin  walled  objects,  depends  on  wall   thickness  (K).  F  =  Kpio i(r -­‐r) E  Ri  gets  larger     • Viscoelastic  materials  have  time  dependent  properties,  contains  both  viscous   and  elastic  properties  that  are  time  and/or  stress  dependent.  (e.g.  silly  putty)   Ø Example:  slug  slime  is  made  of  polysaccharides  and  protein.  It  moves   by  pushing  back  on  its  mucus,  but  changes  to  a  liquid  beyond  a  critical   yield  stress.     Types  of  Materials:   • Bamboo  has  a  bulkhead,  which  prevents  ovalization;  it  is  essentially  a  strong   piece  in  the  center  of  the  stick.     • Wood  is  a  material  that  is  stiff  enough  to  avoid  drooping,  strong  but  flexible,   tough  enough  not  to  shatter  and  light  enough  not  to  buckle.  In  trees,  pre-­‐ stressing  the  wood  in  tension  occurs  when  dead  cells  pull  on  the  tree.     • Toughness  –  resists  crack  propagation,  absorbs  large  amounts  of  energy   without  fracturing,  can  withstand  both  high  stress  and  strain,  has  a  greater   work  of  extension.     • Torsion  –  sheer  and  tension  on  the  outside  but  compression  on  the  inside.   Problematic  in  man-­‐made  materials  but  advantageous  in  biological  materials   like  the  dandelion.     • Wood  and  the  behavior  of  trees  ***research  in  book   • Collagen  not  very  stretchy  but  stores  a  lot  of  materials.  E.g  tendons,  elastic   storage  in  the  gastrocnemius  tendon.  Most  energy  is  returned  to  the  system,   if  there  was  a  larger  area  between  the  two  lines  on  an  energy  curve  that  is   more  energy  lost.     • Bone  –  isotropic,  but  similar  to  wood  mechanically.  Must  resist  loading   forces  from  movement  and  from  muscles  using  them  as  levers.  Constant   remodeling.       Ø Trabeculae  form  along  primary  lines  of  stress  and  remodel  in   response  to  repeated  impacts  to  the  bone.     Ø Antlers  –  high  strength,  high  work  of  fracture,  low  stiffness,   low-­‐density  (low  mineral  content).     Ø Anti-­‐Crack  propagation   1. In-­‐plane  crack  deflection,  out-­‐of-­‐plane  crack  twisting   2. Uncracked  ligament  bridging   3. Deflection  around  hyper  mineralizes  regions  (osteons)   Ø Mollusk  shell  nacre  –  composite:  calcium  carbonate  plates   glued  together  by  a  proteinaceous  matrix,  mostly  minerals  but   much  a  composition  of  materials  makes  these  shells  tougher   than  the  minerals  alone.  Shifting  of  the  plates  absorbs  energy.     Seahorses  Square  Tails  (article  by  Michael  Porter)   • Seahorses  are  not  the  only  animal  with  a  square  tail,  however,  they  are  the   only  square  prehensile  tails.   • The  twisting  of  the  tails  give  them  the  ability  to  wrap  them  up  even  more.   They  have  more  ventral  bending  than  dorsal.   • Porter’s  hypotheses:     1. Square  tail  enhances  grasping  abilities  and  crush  resistance   2. Tail  segment  skew,  ventral-­‐dorsal  overlaps,  and  plate  size  limit  dorsal   bending.   3. Square  shape  performs  “better”  than  circular  tail  shape  during   deformations.   • Types  of  Joints:   Ø Gliding   Ø Elastic  connection   Ø Peg  and  socket  joint   Ø Ball  and  socket  joint   Ø Spring  strut   • Square  is  more  organized,  less  resistance  to  crushing  and  twists  less  than   circular.   • On  a  load  to  displacement  graph,  square  shows  a  steeper  curve  indicating  it   is  steeper.     Muscles:   Types  of  Muscles:     1. Cardiac:  Myogenic  (it  can  generate  movement  from  within  itself)  and  also   neurogenic   2. Smooth  Muscle  usually  myogenic  (stomach,  urinary  ducts)  however,  also   neurogenic  (vessels,  iris,  walls  of  sperm  ducts)   3. Skeletal     • Muscle  contraction  is  caused  by  sarcomeres  changes  length.  Sarcomeres  are   made  up  of  actin  and  myosin,  these  cause  contractions  but  do  not  change   length.     • Muscles  are  made  up  of  multiple  motor  neurons   • Smaller  motor  units  five  finer  muscle  control     Muscle  Contraction:   • Muscles  move  by  doing  work  (measure  in  Joules)   • Muscles  exert  a  force  and  shorten  by  a  distance  (change  in  L)   • Work  per  unit  time  equals  the  power  produced  by  muscles  (Watts,  W)   Power  =  work/  time  –  you  must  have  rate  or  velocity  (direction)  otherwise   you  talk  about  force.     • Work  =force  x  distance     Types  of  Muscle  Contraction   1. Shortening:  concentric  (+  force)   2. Isotonic  Contraction:  force,  tone  is  staying  the  same  (-­‐/0/+)   3. Isometric  Contraction:  no  change  (e.g.  pushing  against  a  wall)  (0)   4. Eccentric  Contraction:  elongation  (-­‐)   *Holding  something  steady  is  both  isotonic  and  isometric         All  myosin  heads   can  attach  to  actin     Actin  &  myosin   are  NOT   overlapping  at   all   Too   much   overlap     Based  on  muscled  function   The  faster  you  go  the  lower   the  force     We  can  increase  the  power   with  springs!                       Shape  of  the  muscle  affects:   • Amount  of  contraction  (distance)   • Velocity  (depend  on  the  number  of  sarcomeres)   • Force  is  a  physiological  cross  sectional  area  (PCSA)   • Power   • Longer  muscles  have  sarcomeres  lined  up  next  to  each  other  or  “in  series”   this  allows  them  to  contract  at  a  greater  distance  and  therefore  give  them  a   greater  velocity,  force  and  power.  


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