Factors Influencing Movement 1. Magnitude of net Torque 2. Inertial characteristics of object such as it’s rotational inertia (I), friction factors 3. Pathway available

Rotary Motion represented by a straight line line starts at the axis of rotation line ends at a selected point on the body or segment being examined

KINEMATICS Linear Rotary v = d/t omega  =  ÷ t alpha  = 2- 1 ÷ t a = v2 - v1 ÷ t d = vt theta  = t

: Angular Velocity How fast a rotating body/segment changes its position measured in radians or degrees per second radian = 57.3 degrees  direction is either cw- or ccw+

v of a Point on Rotating Body important in throwing, kicking, striking r --> radius of rotation --> distance from axis to a selected point linear distance d = r linear velocity v = r

Radius = from trunk longitudinal axis to fingers

“Basic Biomechanics” 4th edition FIG 11-16 page 373 “Basic Biomechanics” 4th edition by Susan J. Hall

Figure H.1 on page 315  is the same for points A, B, and C A, B, C = 2 rads or 114.6 degrees [57.3 x 2]  is the same for points A, B, and C v is not the same for points A, B, and C A, B, C travel @ 4 rads per second r increases from A (0.3) to B (0.6) to C (0.9)

 : Angular Acceleration rare in human motion to have constant  most motion has continual   =   ÷  t  = large change in  in a short time  = small change in  over a long time

Slow Pitcher Fast Pitcher   = 5 radians  t = 0.2 seconds  =   ÷  t   = 20 radians  t = 0.2 seconds  =   ÷  t  = 5 ÷ 0.2 = 25 rads/sec/sec  = 20 ÷ 0.2 = 100 rads/sec/sec

Average  Instantaneous  examining the time it takes for a body, segment, or implement to complete a motion useful in qualitative analysis of motion examining the  at a particular point in the ROM v = r determines the instantaneous v of any point on a system

 = T ÷ I (Newton’s 2nd Law) Rotational Inertia : I Resistance to a change in  (angular accel.) I = mr² OR I = mk²  = T ÷ I (Newton’s 2nd Law) T = I

Examples of I = mr² 1. arm swing with elbows extended/flexed 2. Figure H.3b on page 319 - as r doubles I quadruples 3. turntable demonstration

r of Rotation r of Gyration asymmetrical systems distance from the axis of rotation to a point where all the mass is concentrated I = mk² symmetrical systems distance from the axis of rotation to a precise point on a rotating system v = r