1. 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

2. 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

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

4. : 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+

5. 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

6. Radius = from trunk longitudinal axis to fingers

7. “Basic Biomechanics” 4th edition
FIG page 373
“Basic Biomechanics” 4th edition
by Susan J. Hall

8. Figure H.1 on page 315  is the same for points A, B, and C
A, B, C = 2 rads or 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 4 rads per second
r increases from A (0.3) to B (0.6) to C (0.9)

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

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

11. 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

12.  = 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

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

14. 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