Rotations%20Free%20of%20Support

1
Rotations Free of Support

• Most common in Dance, Diving, Figure Skating,
  Gymnastics, Trampoline
• ML Axis see Figure 15.2a
• L axis see Figure 15.2b
• AP axis see Fig. 15.2c
• flight path of CG determined _at_ takeoff
• airborne segmental motions do not change CG
  flight path see Figure 15.1 on page 494

2
Rotations about ML Axis - page 495 FIG 15.2a
3
Rotations about L Axis - page 496 FIG 15.2b
4
Rotations about AP Axis - page 496 FIG 15.2c
5
CG Flight Path determined _at_ takeoffpage 494 FIG
15.1
6
L Angular Momentum

• L I ?
• ? is angular velocity
• I is rotational inertia - a bodys resistance to
  change angular motion
• I mk²(mass x distance² of mass from axis of
  rotation)

7
Conservation of L

• L stays constant while airborne
• ? changes due to changes in I
• k changes as body moves to pike position then
  back to a layout position

Fig I.5 page 329
8
L I? in Body Rotations

• Angular Momentum Rotational Inertia x ?
• I (rotational inertia) mk²
• 1. m mass of performer (does not change)
• 2. k radius of gyration of performers mass
  
• 3. ? angular velocity of performers rotation
• distribution of m is key feature

9
L constant while airborne

• individual segments may redistribute total bodys
  L
• rotate arms forward, trunk rotates backward so
  total L remains constant
• LJ - rotate trunk downward and legs move upward

• L is established _at_ takeoff
• the entire body has L
• L remains constant during flight until an
  external T acts on bodye.g. floor, water

10
Small segment requires ? ?

• Entire body/system has a magnitude of L created _at_
  takeoff L I ? or L (mk²) x (?)
• L _at_ takeoff due to magnitude of both I and ?
• ? _at_ takeoff due to magnitude of T applied
• m and k of arms much smaller than total body
• to slow/stop trunk rotation, arms rotate with ??
  arms m and k much less than trunk m and k

11
RIGHT-HAND THUMB RULE

• method of determining vector direction
• curve fingers of right hand in direction of
  rotation
• right thumb points in vector direction of L ?
• see Figure E.5 on page 113
• see Figure 15.4 on page 498

12
RIGHT HAND THUMB RULE
FIG E.5 page 113 FIG
15.4 page 498
13
Initiating Rotations from the GroundGRF (ground
reaction force) applied eccentrically
FIG 15.5 Pg 500
14
Initiating Rotations from the GroundGRF (ground
reaction force) applied eccentrically
FIG I.1b Pg 327
15
Initiating Rotations from the GroundGRF (ground
reaction force) applied eccentrically
FIG I.2 Pg 328
16
Initiating Rotations from the GroundGRF (ground
reaction force) applied eccentrically
FIG I.3Pg 328
17
Initiating Rotations from the GroundGRF (ground
reaction force) applied eccentrically
Pg 394 FIG 12.5
18
Initiating Rotations from the GroundGRF (ground
reaction force) applied eccentrically

page 400 FIG 12.10