Waking

• Ground Reaction Forces in Walking - Double Stance:

  • Double stance fore-aft (Fy) vectors in opposite directions
  • Sum of vectors in double support
  • Mostly up, Fy cancels out
  • Fy =vertical force
• Ground Reaction Forces in Walking - Double Stance:

  • A butterfly force diagram shown, force vectors for each foot at a certain time, with the direction (where arrow point), most is vertical
  • If standing still reaction force will be equal to your weight
  • If it more than your weight, you start accelerating up, CoM move up, no weight on ground so more force toward ground so accelerate down
  • Large around ground strike & lower at mid stance
• Ground Reaction Forces in Walking - Stance:

  • Vertical force (Fz) greater than body weight after about 10% of cycle
  • Braking force until mid stance, propulsion after
• Ground Reaction Forces in Walking - Stance:

  • Very beginning & end = very small as foot just started to touch/leave ground
  • Force decreasing in middle part of stance as
  • Push off foot pushing forward, landing foot slowing you down (if didn’t would have net forward force) = forward & backward forces balance out
  • Vertical component 0 on some strides = net vertical force
• Energy During Walking:

  • Potential energy is high when gravitational potential is high, when something is high
  • Have to do work to get it to height
  • Potential energy highest at highest point = stationary & as low at concentric energy
• Energy During Walking:

  • Inversely related/trade off
  • All/high potential energy, low kinetic energy
  • High kinetic, low potential energy
• Energy During Walking:

  • Can model this as walking
  • Fixed point is foot that you tip over (upside down pendulum)
  • Trade off shown
  • CoM has most gravitational potential energy during mid stance, support leg straight, CoM as high as get, as tip over will speed up (kinetic increases)
• Inverted Pendulum Model of Walking:

  • Stance limb as inverted pendulum; swing limb as double pendulum, both pinned at hip
  • Gravity plays important role
  • Fr = v^2/g l
  • g = gravitational acceleration
  • l = leg length
  • When Fr > 1, support limb comes off ground
  • Fr = Force resultant
• Inverted Pendulum Model of Walking:

  • Stance limb inverted pendulum
  • Swing limb normal pendulum
  • Swings to become next stance limb
  • Gravity important for walking
  • Don’t need to memerise equation
  • Fr = Freod number, specific to this kind of model, values in this equation are forward velocity (v), gravitational acceleration (g), the magnitude, length of limb (l)
• Inverted Pendulum Model of Walking:

  • If start moving really quickly
  • Bottom of inverted pendulum start to come off the ground before the next foot touches the ground
  • When ratio exceeds 1 gravity is too low, or stance is to low = running
  • g gets smaller; not gonna change very often
  • Leg length; little legs got to keep up more; changes depending on their size
  • Specific equation to this model
  • Not a fair comparison for speed people different sizes