LINEAR KINEMATICS Flashcards by Tara Track

kinematics

concerned with motion of objects without reference to the forces which cause the motion
-what you can SEE

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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

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where do we place the markers in passive marker-based motion capture

on bony landmarks
-because we are tracking SKELETAL motion

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how many cameras are needed to get xyz coordinates

minimum 2 cameras

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how many dimensions in passive marker-based motion capture

3D reconstruction of 2D images
-multiple cameras collect different perspectives

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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

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in passive marker-based motion capture we sample continuous/discrete time points

discrete

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frame rate

sampling frequency
-how frequently the camera is taking an image

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if you have a fast movement, you want a slower/faster frame rate

faster
-otherwise you will miss some of the movement

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shutter speed

time the shutter is open

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fast shutter speed = too light/dark

dark but clearer

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time series data

a collection of. observations for a single subject at different time intervals
-generally equally spaced

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noise

-points that wiggle around the true value
-fluctuations in the data that aren’t real

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distance

length traveled along a path
-cumulative across changes in direction

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is distance a scalar or vector

scalar

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position

location with respect to an origin/comparison point

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is position a scalar or vector

vector

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position is denoted as…

s(t)

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displacement

change in position

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is displacement a scalar or vector

vector

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displacement is denoted as…

∆s(t)

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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

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center of pressure trace

using a force plate to look at quantitative measures of balance

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better balance = looser/tighter COP trace

tighter COP trace

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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 = ?

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

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