chapter 11 angular kinematics of human movement · • distinguish angular motion from rectilinear...
TRANSCRIPT
Chapter 11 Angular Kinematics of
Human Movement
Basic Biomechanics, 4th edition Susan J. Hall
Presentation Created by TK Koesterer, Ph.D., ATC Humboldt State University
Objectives • Distinguish angular motion from rectilinear and
curvilinear motion
• Discuss the relationship among angular kinematic variables
• Correctly associate associate angular kinematic quantities with their units of measure
• Explain the relationship between angular and linear displacement, angular and linear velocity, and angular and linear acceleration
• Solve quantitative problems involving angular kinematic quantities and the relationship between and linear quantities
Observing the Angular Kinematics
• Clinicians, coaches, and teachers of physical activities routinely analyze human movement
• Based on observation of timing and range of motion
• Developmental stages of motor skills are based on analysis of angular kinematics
Measuring Angles
• Filmed images
• Videotapes and films of human movement
• Computer software
11-1
Relative versus Absolute Angles
Relative angle:
• Anatomical reference position
Absolute angle:
• Horizontal reference
• Vertical reference
11-2
11-3
Tools for Measuring Body Angles
Goniometer:
• One arm fixed to protractor at 00
• Other arm free to rotate
• Center of goniometer over joint center
• Arms aligned over longitudinal axes
Electrogoniometer (elgon):
Inclinometers:
Instant Center of Rotation
Instant Center:
• Roentgenograms (x rays)
• Instrumented spatial linkage with pin fixation
Example:
Instant center of the knee shifts during angular movement
11-4
Angular Kinematic Relationships Angular Distance & Displacement
• Assessed as difference of initial & final positions
– Counterclockwise is positive
– Clockwise is negative
• Human’s also indicate with joint-related terminology
• Measured in
– Degrees, radians, or revolutions
Radian
Angular Kinematic Relationships Angular Velocity
Angular velocity = angular displacement ω = θ
change in time Δt
Units: deg/s, rad/s, rev/s, & rpm
Angular Kinematic Relationships Angular Acceleration
Angular acceleration = change in angular velocity
change in time
α = Δ ω
Δt
Units: deg/s2, rad/s2, & rev/s2
Angular Kinematic Relationships
Angular Motion Vectors • Right hand rule
Average vs. Instantaneous Angular Quantities
• Angular speed, Velocity, & Acceleration
Right Hand Rule
Relationship Between Linear and Angular Motion
d = rӨ
Radius of rotation:
• Linear distance & radius of rotation same units
• Angular distance in radians
Radius of Rotation
Linear and Angular Velocity
V = rω m/s = (m) (rad/s)
• With all other factors held constant, the greater the radius of rotation at which a swinging implement hits a ball, the greater the linear velocity imparted to the ball
However, the magnitude of the angular velocity figures as heavily as the length of the radius of rotation in determining the linear velocity of a point on a swinging implement
Linear and Angular Acceleration
Tangential acceleration:
at = v2 - v1 / t
at = rα
Radial acceleration:
ar = v2 / r
at
ar
Summary
• The angular kinematic quantities - angular displacement, angular velocity, and angular acceleration - possess the same interrelationship as their linear counterparts
• Angular kinematics variables may be quantified for the relative angle formed by the longitudinal axes of two body segment articulating at a joint, or for the absolute angular orientation of a single body segment with respect to a fixed reference line
The End