Angular Kinematics Flashcards
angular/rotational motion
all parts of the body/object move along a circular path about an axis
internal axis
axis through hip joint
external axis
gymnastics bar
real axis (and internal)
bike wheel
imaginary axis
track
absolute angles
measured from immovable line (constant)
relative angles
measured between segments
clockwise (CW) movement
negative
counterclockwise (CCW) movement
positive
right hand rule
- fingers curl in the direction of the rotation
- thumb = vector representing motion
what is general motion?
combination of linear and angular motion
measuring joint angles - flexion
positive (exception: knee)
measuring joint angles - extension
negative
why is the Q-angle larger in women than men?
wider pelvis relative to leg length
large Q-angle
patellofemoral pain due to extreme patellar tracking
radian
size of the angle when the arc length is equal to the radius (57.3 degrees)
how many pi are in a circle? (360 degrees)
2 pi
angular position (θ)
orientation of a line w respect to another line or plane
angular displacement (Δθ)
difference in the initial and final angular positions
avg angular velocity (ω)
rate of change in angular position
angular speed
angular distance / change in time
avg angular acceleration (α)
rate of change of angular velocity
is angular displacement a vector quantity?
yes
angular distance
sum of all angular changes
angular displacement
difference between the initial and final positions
positive angular acceleration
- increasing angular velocity in the + direction
- decreasing angular velocity in the - direction
negative angular acceleration
- increasing angular velocity in the - direction
- decreasing angular velocity in the + direction
what is the slope of an angular position vs time graph?
angular velocity
what is the slope of an angular velocity vs time graph?
angular acceleration
inexperienced paddle boarders
shoulder ROM > hip ROM
experienced paddle boarders
greater shoulder motion & elbow extension positions at end of paddle stroke
experienced batters, pitchers, tennis players
faster joint angular velocities
how can athletes increase performance?
faster segment movement = faster movement of ball, bat, etc.
how does the rotation of the limb affect the object?
increase radius > increase curvilinear distance > increase velocity
curvilinear distance (s)
Δs = rΔθ
m = (m)(radian)
greater radius
greater linear distance traveled
curvilinear velocity (VT)
VT = rω
m/s = (m)(rad/s)
T/F: as a n object rotates around an axis, all parts of the object rotate at the same angular velocity but at different linear velocites
True
what does the linear velocity of a rotating point depend on?
its distance from the axis of rotation
T/F: as an object rotates around an axis, all parts of the rigid object rotate at the same angular velocity but at different linear velocities
True
an object is accelerating when it is:
- speeding up or slowing down (change in velocity)
- changing direction
what is the angular acceleration when the angular velocity is constant?
angular accel = 0
tangential acceleration (aT)
linear acceleration of a point on a rotating object that acts tangentially to the path
when is tangential acceleration not zero?
when a point is speeding up or slowing down (represents change in linear v)
radial (centripetal) acceleration
- toward center of circle, axis of rotation
- represents change in direction
is more or less force needed to produce radial acceleration?
more force
two factors that make it difficult to stay on a curved path:
1) smaller radius
2) greater tangential velocity
is there an angular acceleration when the angular velocity is constant?
No, constant angular velocity = no angular acceleration
is there linear acceleration when the angular velocity is constant?
Tangential acceleration: no
Radial acceleration: yes, because there will still be a change in direction so the object experiences accel.
projectile at release
- tangential acceleration becomes zero
- radial acceleration becomes zero
- VT = VRi
are tangential and radial accelerations parallel or perpendicular to one another?
perpendicular
if angular velocity is constant
- tangential velocity is constant
- acceleration = 0
if angular acceleration is zero
- tangential acceleration = 0
- radial accel. and tangential vel. will have magnitudes
