LINEAR KINEMATICS Flashcards
kinematics
concerned with motion of objects without reference to the forces which cause the motion
-what you can SEE
passive marker-based motion capture
-put a bunch of markers on body + track them with video cameras around the room
-markers on the body aren’t sensors because they don’t emit their own light; they reflect light back to the cameras that capture their position
-the camera is what emits light, the marker just reflects it
where do we place the markers in passive marker-based motion capture
on bony landmarks
-because we are tracking SKELETAL motion
how many cameras are needed to get xyz coordinates
minimum 2 cameras
how many dimensions in passive marker-based motion capture
3D reconstruction of 2D images
-multiple cameras collect different perspectives
what is the camera made of
infrared LEDS + lens with infrared filter
-infrared light shines onto marker, which sends reflected light back to the camera
in passive marker-based motion capture we sample continuous/discrete time points
discrete
frame rate
sampling frequency
-how frequently the camera is taking an image
if you have a fast movement, you want a slower/faster frame rate
faster
-otherwise you will miss some of the movement
shutter speed
time the shutter is open
fast shutter speed = too light/dark
dark but clearer
time series data
a collection of. observations for a single subject at different time intervals
-generally equally spaced
noise
-points that wiggle around the true value
-fluctuations in the data that aren’t real
distance
length traveled along a path
-cumulative across changes in direction
is distance a scalar or vector
scalar
position
location with respect to an origin/comparison point
is position a scalar or vector
vector
position is denoted as…
s(t)
displacement
change in position
is displacement a scalar or vector
vector
displacement is denoted as…
∆s(t)
center of pressure
point of application of that ground force
-all the load being transmitted between that person + the ground is transmitted through the COP
center of pressure trace
using a force plate to look at quantitative measures of balance
better balance = looser/tighter COP trace
tighter COP trace
velocity
change in position over time
velocity is a scalar or vector
vector
velocity is the derivative of…
position
-velocity = slope of the line tanget to the position function
acceleration
change in velocity over time
acceleration is a scalar or vector
vector
acceleration is a derivative of…
velocity
-acceleration = slope of line tangent to velocity function
acceleration is second derivative of…
position
if position curve cups up, acceleration is positive/negative
positive
-cups down = negative
inflection point
point where curvature of the function goes from curved up to down + vice versa
if position graph is at local min/max, velocity = ?
0
peak bar velocity
-people often use bar velocity to determine the power of their movement
-peak bar velocity is the instant in time when velocity is maximum (instantaneous velocity)
average velocity
calculated as a change in displacement over a time interval
instantaneous velocity
more discrete measure of velocity measured at a given moment in time
-change in time is infinitesimally small
numerical differentiation
computing the slope of the line tangent to a curve for time series data (aka derivative)
what is numerical differentiation used for
to calculate instantaneous velocity from discrete time series data
central differencing method
used to numerically differentiate time series data
-ex: calculating instantaneous velocity at time point 2
constant acceleration
acceleration is nonzero but constant
examples of constant acceleration
-projectile motion (batted ball, shotput throw, soccer shot, high jump, diving, human cannonball stunt)
-friction (Olympic sport culing, sliding into home plate, hockey stop)
projectile
a body in free fall that is subject only to the forces of gravity + air resistance
CLASSIC projectile motion
object is being projected from the same height that it lands at
GENERAL 1 projectile motion
object is projected from a height ABOVE where it lands
GENERAL 2 projectile motion
object is projected from a height BELOW where it lands
VERTICAL projectile motion
object goes straight up + comes stright back down
-no horizontal aspect
HORIZONTAL projectile motion
object is projected at 0 degrees off a ledge/cliff
-gains vertical velocity
factors that affect projectile motion
-projection height
-projection angle
-initial speed
OR
-initial vertical velocity
relative projection height
the difference between projection height + landing height
projection speed
magnitude of projection velocity
what determines height of trajectory apex of projectile
initial vertical velocity
what determines horizontal distance covered of a projectile
initial horizontal velocity
angle of projection
the direction at which a body is projected with respect to the horizontal
what is determined by angle of projection
relative magnitude of vertical vs horizontal components of velocity
what will happen to a projectile if it has a large vertical velocity
object will fly very high but won’t go very far
what will happen if a projectile has equal components of vertical + horizontal velocity
longer distance traveled but not as high of an apex achieved
-this is the best option because balance
what will happen if a projectile has large horizontal velocity
neither a high apex nor long horizontal distance traveled
what is the most ideal projection angle (in terms of vertical + horizontal projection angles)
equal components of vertical + horizontal velocity
CLASSIC SITUATION:
relative height h = ?
h = 0
CLASSIC SITUATION:
optimum angle
45 degrees
GENERAL SITUATION:
relative height h = ?
h ≠ 0
GENERAL SITUATION:
if relative height increases, angle increases/decreases
decreases
GENERAL SITUATION:
if relative height decreases, angle increases/decreases
increases
SHOTPUT THROW:
goal
maximize horizontal displacement
SHOTPUT THROW:
general case
height advantage
LONG JUMP:
goal
maximize horizontal displacement
LONG JUMP:
general case
technically height advantage because COM is lower when hits ground than at start
BASKETBALL FREE THROW SHOT:
goal
accurately hit hoop/make basket
BASKETBALL FREE THROW SHOT:
general case
height deficit
consider 2 balls- 1 dropped vertically + 1 projected horizontally from same height:
describe when each hits the ground
-both hit the ground at the same time because the vertical + horizontal components are independent of each other
-gravity affects their vertical velocities equally
horizontal + vertical components are dependent/independent of each other
independent
when does horizontal component change
only if air resistance is not negligible
apex
highest point in the trajectory of a projectile
-projectile motion is symmetric on either side of an apex, parabolic
describe projectile without air resistance
-higher apex
-larger horizontal displacement
-symmetric trajectory
describe projectile with air resistance
descent of projectile is steeper/asymmetric compared to initial portion
acceleration during free fall
-9.81 m/s^2
which of the following is not a target muscle in the reverse scoop medicine ball throw?
-quadriceps femoris
-anterior deltoid
-gluteus maximum
-gastrocnemius
-trapezius
trapezius
which is a characteristic of young/active fascia versus older/inactive fascia in terms of its structure
-bidirectional lattice structure
-multidirectional crimp structure
bidirectional lattice structure
the reverse scoop medicine ball throw strengthens which anatomy train
superficial back line
which of the following is NOT part of the superficial back line
-plantar fascia
-erector spinae
-gastrocnemius
-latissimus dorsi
latissimus dorsi
which of the following will stretch the superficial back line?
-seated twist
-standing forward bend
-reverse plank
-bow stretch
standing forward bend
true/false: the overall movement function of the superfical back line is flexion + twisting
false
in quantifying the maximum velocity of hand during the pitch motion in softball you are looking to quantify an
-instantaneous velocity
-average velocity
instantaneous velocity
to make sure you do not miss the time point (or event) you care most about in a movement you should do which of the following
-increase shutter speed
-increase focal length
-increase aperture
-increase frame rate
increase frame rate
when trying to record movement data in 3D dimensions how many vantages (perspectives) do you need at minimum to percieve all 3 dimensions (x, y, z coordinates) of a marker
2
true/false: in passive marker based motion capture the markers emit their own light
false
if an projectile lands ABOVE where it was projected from, describe optimal angle of projection
more than 45 degrees
if a projectile lands LOWER than projection height, describe optimal angle of projection
less than 45 degrees
true/false: all else held constant, increasing the horizontal velocity in projectile motion will increase the horizontal displacement but not the flight time
true
if you have a height advantage, what must you do to optimal angle
lower it
if you have a height disadvantage, what must you do to optimal angle
increase it
shoput throw is height advantage/disadvantage
height advantage
long jump is height advantage/disadvantage
height advantage
basketball free throw is height advantage/disadvantage
height disadvantage
what determines flight time
-projection height
-projection angle
-initial speed
-initial vertical velocity
does initial horizontal velocity affect flight time?
no
-partially determines horizontal distance travelled
it is easier for the body to generate horizontal/vertical force
horizontal
