FINAL Flashcards
first central difference
v = p/t
we plot in b/w times i.e. 5+4/2 = 4.5
however, FCD:
- use larger time frame to have an EXACT moment/velocity at a time
- still avg velocity, just larger
instantaneous velocity
no change in time, velocity at one pt in time
draw a tangent line and find when there’s a single overlap on the graph
- if tangent line somewhat flat, means there is low change in position
what reference system used
cartesian reference system
use coordinates to locate a point
coordinate method
- use global reference system
- pt P is specified
- location of P is found using reference system
how to collect data for mvmnt? veloc accel
use HIGH-SPEED camera, high frame rate/s
put markers on boney prominences/markings i.e. white dots
define global reference system/smth relevant to the study
what is linear kinematics
position, velocity, acc, displacement
motion: when object changes position
how to visually estimate velocity and acceleration
- see points of inflection
- mins/max
- v=0 at POI, put it on x-axis for velocity - sign of slope
- signs match, must approach zero - steepness
- if og shape is steep, velocity is STEEPER
shuttle run graph
v=0 in middle when halfway, direction change occurs
- +ve forward and -ve backward directions
even when slowing down, DIRECTION is still positive or negative
- velocity sign does not change
HOWEVER, decreasing +ve velocity means -ve acceleration (bcs ROC of v is dec)
CONCLUSIONS:
- velocity is dependent on direction
- acceleration is independent of direction, since -ve A can occur without a direction change (depends on velocity)
angular motion
body parts move thru same angle, but don’t undergo SAME linear displacement
occur about an axis of rotation
what is each marker called
proximal
vertex (middle, axis of rotation)
distal
relative joint angle
angle b/w 2 longitudinal axes of 2 segments
do NOT describe the position of the segment in space
- i.e. can be 60deg at many diff places, positions
- doesn’t say orientation
absolute angles
angle of inclination of a body segment relative to a fixed reference/horizontal i.e. ground
only needs prox and dist
DOES tell where you are in space
stride vs step
stride: heel to same heel, successive points of INITIAL CONTACT of same foot
- i.e. 2 steps
- 60% stance, 40% swing
step: heel to opp heel
- initial contact of one foot to initial contact of other foot
step width
lateral distance b/w successive points of contact of OPP feet
foot angle
angle b/w line of progression (straight line walking forward) and line b/w midpoints of calcaneus and 2nd MT head
- at rest, angle is 0 (toes straight)
- -ve angle is pigeon toe/anime girl stance
- +ve angle when point outwards/elf stance
gait cycling time
allows us to see gait disorders
- analyze and track compared to baseline
- see asymmetry
- see abnormal cadence i.e. for age, sex, etc.
- improper time in double or single stance
- discover risk of falling
cadence
steps/minute
how to increase velocity i.e. walk to run
- inc stride length
- inc cadence (steps/min)
- do both
this causes stance time to dec, swing time to inc
anatomical angle
relative angle is compared to angle of the joint in anatomical position (180)
rearfoot angle
examining frontal plane
at rest, leg and calcaneus 90deg
uses 2 absolute angles, of leg and calcaneus
pronation:
- dorsiflexion, sag
- EVERSION, front
- abduction, hori
supination:
- plantarflex
- adduct
- INVERSION
center of gravity
the point where all particles of the body are evenly distributed
center of mass
point where all the body’s MASS is evenly distributed
reaction board method
person lays on 2m board, with feet on fixed axis of rotation
free body diagram
link b/w complexity of human situation and application of mechanic techniques
essential feature of FBD
isolation of a segment
inclusion of forces working on the segment, including GRF
steps to develop FBD
- isolate segment from rest of body
- identify reference system
- put on weight forces
- -ve direction of segment
- always has weight, not necessarily other forces - include external/unknown forces acting on seg
- check forces
- apply equilibrium equn and solve for unknown
assumptions of FBDs
- person is static
- all forces are acting on same 2D plane (no Z direction)
- all joints are hinge, bcs 2D motion
- all muscles are represented as single muscle equivalent…all are considered as primer mover
- unknown forces acting in pos direction
COMx equn
COMx = Xp + (COM/SLp)(Xd - Xp)
COMy
COMy = Yp + (COM/SLp)(Yd-Yp)
rearfoot angle equn
rearfoot angle = abs angle of leg - abs angle of calcaneus
absolute angle equn
theta = tan(Yprox-Ydist/X prox-Xdist)
