Intro / Linear Kinematics Flashcards
what is biomechanics?
study of forces and their effects on living systems
statics
mechanics of objects at rest or in uniform motion
uniform motion
constant velocity, > 0m/s
acceleration is zero
dynamics
mechanics of objects in accelerated motion
kinematics
description of motion independent of the cause (what we observe)
kinetics
forces that cause or change motion
sagittal plane
vertical and AP axis
frontal plane
vertical and ML axis
transverse plane
AP axis and ML axis
linear motion (translation)
along an axis
angular motion (rotational)
- around an axis
- fixed axis
- paths different lengths
plane
a 2D surface defined by 3 points not on the same line (not colinear)
motion
process in change in position over time
rectilinear motion (rare)
motion along a straight line or path
curvilinear motion (common)
- motion along a curved line or path
- no fixed axis
- paths same length
examples of angular motion
leg raises (internal axis)
swinging from a bar (external axis)
qualitative kinematic analysis
visual observation of motion
quantitative kinematic analysis
measurement
most commonly used spatial reference system
Cartesian coordinate system
global coordinate systems
1D, 2D, 3D
local coordinate systems
relative angle & absolute angle
relative angle (joint angle)
local CS relative to another local CS
absolute angle (segment angle)
global GS relative to a local CS
scalar
magnitude only
vector
magnitude & direction
linear position
- location in space
- avg or instananeous
- ref point needed
example of linear position
shuttle run (no displacement)
distance (l)
- length of the path of motion
- scalar
displacement (d or delta s)
- change in position in a specific direction
- vector
displacement equation
Δs = s final - s initial
use of distance in gait analysis
left side stroke, shorter right step
what is a runner’s displacement if they compete:
a) one lap
b) ten laps
c) 1/2 lap
a) 0 m
b) 0 m
c) 200 m
calculating linear displacement with two coordinates
1) Δy = yf - yi, Δx = xf - xi
2) d = √Δx^2 + Δy^2
calculating direction (angle of resultant)
SOH CAH TOA
speed
- how fast a person or object is moving
- scalar
speed equation
speed = distance / time
velocity
- how fast a person or object is moving in a specific direction
- vector
velocity equation
velocity = displacement / change in time (Δposition / Δtime)
What is the resultant velocity if it tok a hiker 13 hrs and 45 min to hike from Yosemite National Park to Lake Tahoe?
Map: 77 miles 60 degrees N of W = resultant displacement
1) convert miles to m and time to sec
2) v = Δposition / Δ time
v = 123919 m / 49500 sec
v = 2.5 m/s, 60 degrees N of W
3) direction: break into x and y components
y-component = 2.5sin60 = 2.17 m/s N
x-component = 2.5cos60 = -1.25 m/s W
T/F: a change in the body’s velocity may represent a change in its speed, movement direction, or both
True
example of linear speed
gait speed
gait speed
stride length x stride frequency
increasing one or the other increases gait speed
A runner completes 6 1/2 laps around a 400 m track that has a diameter of 160 m. It takes the runner 12 min (720 s) to complete the run. Calculate the following:
a) distance covered
b) displacement at the end of 12 min
c) average speed
d) average velocity
a) 2600 m
b) -160 m or 160 m south
c) 3.61 m/s
d) -0.22 m/s
most economical runner
lowest submaximal oxygen consumption (VO2)
most economical trunk angle
greater trunk lean (5.9)
most economical max. knee flexion in support
greater knee flexion (43.1)
most economical wrist excursion
- medium wrist excursion (80.7)
- “goldilocks zone”
most economical vertical oscillation
lower levels of vertical oscillation (9.1)
Brian is trying to swim in the ocean from west to east at a velocity of 1.5 m/s. However, the water current is pushing him at an angle of 20 degrees west of south at a velocity of 0.5 m/s. What is Brian’s resultant velocity?
1) break into x and y components
2) SOH CAH TOA
3) sum x components and y components separately
4) plug into resultant velocity equation
Vr = 1/41 m/s
θ = 70.53 degrees east of south
linear acceleration
the change in motion of an object
acceleration equation
acceleration = change in velocity / change in time (Δv / Δt)
EXAM: acceleration may be positive, negative, or zero, based on:
- direction of motion
- change in velocity (slowing down, speeding up)
case 1: speeding up in the positive direction
+ velocity
speeding up
+ acceleration
(+)(+) = (+)
case 2: slowing down in the positive direction
+ velocity
slowing down
- acceleration
(+)(-) = (-)
case 3: speeding up in the negative direction
- velocity
speeding up - acceleration
(-)(+) = (-)
case 4: slowing down in the negative direction
- velocity
slowing down
+ acceleration
(-)(-) = (+)
If a runner is slowing down in the positive direction: what is acceleration?
negative
(+)(-) = (?)
A runner’s final velocity is positive: Running in the positive direction. Acceleration is negative. Is the runner speeding up or slowing down?
slowing down
(+)(?) = (-)
+ velocity, + acceleration
speed is increasing (speeding up)
- velocity, - acceleration
speed is decreasing (slowing down)
Andrea is running at a speed of 3.0 m/s in the negative direction at time 4 s. Her acceleration between time 4 s and 6 s was -2.5 m/s^2. Was she slowing down or speeding up?
speeding up
(-)(?) = (-)
or
a = Δv / Δt
solve for vf
to be able to identify sign (direction of acceleration, need to know:
- direction of motion (sign of velocity)
- if v is increasing or decreasing (speeding up/slowing down)
to be able to identify if person/object is speeding up/slowing down, need to know:
- direction of motion (sign of velocity)
- sign of acceleration
