1. Angular motion
Principles 6 & 7

2. Learning goals We are learning what angular motion (torque) is.
We are learning to apply angular motion to sport specific examples.
We are learning to describe angular momentum.
We are learning to apply angular momentum to sport specific activities.

3. background Circular motion occurs: around an axis of rotation
when a force is applied a distance from the center of mass
Recall the axis:
horizontal, longitudinal, antero-posterior

4. concepts 1. When a body moves around a joint
the axis of rotation passes through the middle of the joint
e.g. forearm around elbow
2. When the whole body is rotating in contact with the ground
the axis of rotation is the point of contact
e.g. cartwheel

5. concepts 3. When the body is airborne
all axes pass through the body’s centre of mass
e.g. diving
4. Moment or Torque
the force applied at a distance from the C of M to cause spinning around an axis
e.g. football

6. concepts 5. Moment of Inertia
a measure of the resistance to angular motion
decreases when closer to axis
e.g running - legs closer to hip during recovery
e.g. figure skating - bring hands into towards body

7. concepts 6. Angular Velocity
how fast a body segment is turning around an axis
7. Angular Momentum
the amount of angular motion
Angular Momentum = Angular Inertia x Angular Velocity

8. A Comparison of Linear and Angular Motion Terms
LINEAR MOTION
ANGULAR MOTION
Force
Moment or Torque
Inertia (mass)
Moment of Inertia
Velocity
Angular Velocity
Momentum
Angular Momentum

9. Principle #6: Angular motion
Angular motion is produced by the application of force (torque) acting some distance from an axis
Applications:
diving
front somersault

10. Angular motion How much momentum produced depends on
1) an axis (point of rotation),
2) a force,
3) the force acting at a distance from the axis.

11. Angular motion
an athlete or an object spins, swings, twists or rotates around an axis of rotation
Spinning
Swinging
Twisting
Rotating

12. Axis of rotation can be…
Around joint when body moves through motion (ie. Throw)
Point of contact with the ground (ie. Somersault, pole vault)
If body is airborne – through centre of gravity (ie. dive)

13. Magnus effect
the name given to the physical phenomenon whereby an object's rotation affects its path through a fluid

14. spinning

15. Using the Magnus Effect to Curve a Ball

16. Principle #7: Conservation of Angular Momentum
the amount of angular momentum (or the amount of turning around an axis) is constant after take-off

17. but
athletes can change their angular motion when in the air or on low friction surfaces by changing their MOMENT OF INERTIA
if this is changed the angular velocity will also
if you bring your arms close to your axis of rotation, you will immediately turn faster since you have reduced angular inertia
the opposite occurs when you extend your arms or legs

18. Angular Momentum = Angular Inertia x Angular Velocity how much spin = a body’s resistance to turning x its speed of turning AM = AI x AV

20. Well …
Speeding up
AM = AI x AV
Slowing Down

21. In summary
a body once set spinning will continue spinning indefinitely with
the same angular momentum unless an external force causes change.
therefore internal forces (contracting muscles) have no effect on it

22. applications
divers
running
vaulting
high bar
figure skater

23. Where does the diver use linear motion?
At the same time she initiates rotation. How does she do this??
What causes the diver to spin faster?
Where does the extra angular velocity come from?

24. Learning goals We are learning what angular motion (torque) is.
We are learning to apply angular motion to sport specific examples.
We are learning to describe angular momentum.
We are learning to apply angular momentum to sport specific activities.