Lecture 30 - Freely Rotating Bodies I Flashcards
1
Q
what are the 2 characteristics of airborne activities relating to forces?
A
- the center of mass follows a parabolic pathway
- the angular momentum is constant
2
Q
when rotation occurs in the air, where must each of the axis of rotation pass through?
A
- the center of mass
- can use all 3 principle axes simultaneously
3
Q
how can movement occur while airborne, if the angular momentum is constant?
A
- as long as the segment motions are symmetrical, angular momentum in each anatomical plane will be constant
4
Q
what is the radius of gyration?
A
- L = mk^2w
- where L = angular momentum (constant)
- where m = mass of the body (constant)
- where w = angular velocity
- where k^2 = radius of gyration
5
Q
how does changing the radius of gyration affect angular velocity?
A
- radius of gyration bigger = smaller angular velocity
- radius of gyration smaller = bigger angular velocity
6
Q
how do we generate angular momentum?
A
- move our segments with muscle power
- any angular momentum generated in one segment is counter-acted by the opposite angular momentum in the remaining segments (aka, can be relocated but not removed from the whole body sum of angular momentum)
- angular momentum is generated at take-off
7
Q
what is takeoff?
A
- the last chance to apply reaction forces and generate angular momentum
8
Q
how can gymnasts/divers use the cat technique?
A
- bend their body on an axis (ex: pike, side arch or back arch)
- this creates asymmetry so angular movement can transfer from one plane to another
9
Q
how can you determine the rotation axes as vectors when drawing the components of the overall angular velocity vector?
A
- using the right-hand rule
10
Q
what can you determine from athletes when you see asymmetry?
A
- the athlete is transferring rotation from one axis to another
- a crash might be imminent
