# 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