KHS 301 Lecture 8: Linear Kinematics, Motion Capture, Linear Motion

Kinematics

the branch of dynamics concerned with the description of motion

Motion

the process of changing position

Motion Analysis

• Science of comparing sequential skill images captured from photo graphing a body in motion

• Calculate angular & linear displacement, distance, joint position & ROM, velocity, speed, acceleration, 2D/3D

Two-Dimensional Motion Analysis

• X & Y axes

• Frames = 50-60 Hz

• Qualitative analyses, limited quantitative analyses

• Calibration - reference object (1m) captured in view & converted to pixels

Calibration in 2D

reference object (1m) captured in view & converted to pixels

Three-Dimensional Motion Analysis

• Multiple cameras - x, y, & z axes

• High-speed cinematography- 100 to > 500 Hz

• Calibration: reference static or dynamic objects of known dimension with multiple markers

Calibration in 3D

reference static or dynamic objects of known dimension with multiple markers

Preferred for Motion Analysis

3D Motion Analysis

Digitization

Conversion of parts of image to numerical position data (frame-by-frame)

- Manual - cursor is moved, "clicked", & marked

- Automatic - reflective markers are automatically defined

Manual Digitization

cursor is moved, "clicked", & marked

Automatic Digitization

reflective markers are automatically defined

How many Data points/sec would be generated at 50 Hz with using 15 markers?

750 data pts/sec

Linear Motion (Translation)

all points on body or object move same distance, in the same direction, at the same time

- Rectilinear

- Curvilinear

Rectilinear

linear motion

Curvilinear

curved pathway

Example of a Curvilinear Motion?

Long Jump

Angular Motion (Rotational, Rotary)

all points on a body or object move in circles about same axis

Examples of Angular Motion

- Isolated limb movements

- Somersault

- Ball rotation

- Golf drive

- Baseball/softball swing

General Motion

Combining Angular and Linear Motion

Examples of General Motion

extension of knee (angular) & flexion of hip (angular) produces linear motion of body

Linear Kinematics

- Position

- Displacement and Distance

- Speed and Velocity

- Acceleration and Deceleration

Position

• "Location in space"

• Describes object location in athletics

- Position of players, position during running, jumping, throwing, lifting, joint or body segment position (ROM)

• Coordinate system (reference system)

Cartesian plane (coordinate plane)

Consists of origin, x & y axis, & a coordinate point (X,Y) in 2-D plane, + axis (Z) in 3-D

- Rene Descartes

- Used to coordinate position

Distance

measure of total length of path followed

Displacement

straight-line length in a specific direction from initial to final position

- Vector quantity

Speed

rate of motion in relation to distance"

Speed Equation

Δ distance / time (m/sec)

Velocity

"rate of motion in a specific direction in relation to displacement"

Velocity Equation

Δ displacement / time (m/sec)

- Vector quantity

instantaneous speed

The rate at which an object is moving at a given moment in time

Phases of Sprinting

Acceleration, Maximum Speed, Deceleration