1. The production of angular motion
Principle 6

2. Note Only copy info from slides with an * to left of the title!
Please read and understand all other slides as it is important, descriptive info!

3. Learning goals We are learning what angular motion (torque) is.
We are learning to apply angular motion to sport specific examples.

4. *Angular motion
Momentum can be gained in a linear direction (ie. running forward), but it can also be generated in a circular direction (ie. spin).
*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.

5. *Angular motion
*Angular motion refers to motion around an axis of rotation. The turning effect produces a force is called torque.
*Angular motion means that an athlete or an object spins, swings, twists or rotates around an axis of rotation
Twisting
Spinning
Swinging
Rotating
All angular motions of athletes or objects in sport are produced by torque.

6. *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)

7. Centric Force
A centric force moves through an object’s centre of gravity and causes a change in the linear movement of the object.
No spin on a ball occurs when the force is directed through the ball’s centre of gravity.

8. Centric Force
A ball with no spin floats through the air. The pressure around the ball remains consistent.
RELATIVE AIR FLOW
The ball is much more vulnerable to the forces of oncoming air and its motion is difficult to predict

9. Eccentric Force Initiating Rotation
An eccentric force does not move through an object’s centre of gravity and causes a change in the linear and angular motions of the object.
Any time a force is applied away from the axis it produces a rotating effect (torque).
Increasing the distance of the force results in a greater turning effect.

10. Eccentric Force Initiating Rotation
To apply spin the server must apply a force away from the ball’s centre of gravity and initiate rotation on the ball.
This produces a Magnus (lift) force and the ball arcs downward in flight.
The farther she applies the force from the ball’s centre of gravity the greater the spin and the faster the ball arcs downward.

11. *How Athletes Make Themselves Rotate
To rise vertically the impulse must go through his centre of gravity.
*An athlete who wants to rotate in the air uses an eccentric force.
*He must position his body so that the impulse does not go through his centre of gravity. The torque that is produced causes him to rotate.

12. The Magnus Effect Any spinning object generates a lift force.
As a spinning ball moves through the air, it spins a boundary layer of air that clings to its surface as it moves.
Any spinning object generates a lift force.
On one side of the ball, the boundary layer collides with the passing air causing it to decelerate, creating an area of high pressure.

13. The Magnus Effect
On the opposite surface the boundary layer moves in the same direction as the passing air (so there is no collision) and it moves faster creating a low pressure area.
The pressure differential, creates a lift force that causes the ball to move in the direction of the pressure differential.
The spinning ball will move toward the area of low pressure and assist gravity.

14. The Magnus Effect Back Spin
Some sports require the athlete to use backspin rather than top spin.
The angle of the club face and the stroke technique will initiate rotation giving it backspin, causing it to rise.

15. The Magnus Effect Back Spin
High pressure area forms under the ball, giving the ball lift.
The added lift will fight gravity allowing the ball to stay in the air longer.

16. Using the Magnus Effect to Curve a Ball

17. *Rotary Inertia
All objects or athletes resist rotation or continue rotating once torque is applied.
32 oz
36 oz
1. The mass of the object.
The more mass an object has the more resistance it has to rotate and the greater persistence it has to continue rotating once rotation has started.
Two important factors that determine how much inertia a rotating object will have:
2. The radial distribution of mass
The farther the mass is from the centre of an object’s axis the more resistance it has to rotate, and the greater the persistence it has to continue rotating once rotation has started.

18. Manipulating Rotary Inertia
The diver in an extended body position must overcome a great deal of rotary inertia before they are able to rotate.
If she pulls her body into a tight tuck position and reduces rotary inertia she will rotate much faster.

19. Manipulating Rotary Inertia
In order to control a spin twist or somersault the diver must use her arms and/or legs to control the rate of spin.

20. Principle 6: Angular Motion
*Summary
The amount of spin applied to an object depends on how much force is applied and how far it is applied from the ball’s centre of gravity.
The greater the force and the larger the distance from the centre of gravity, the greater the torque and the greater the spin.
Angular motion is produced by the application of force or torque acting at some distance from an axis.
Principle 6: Angular Motion

21. Learning goals We are learning what angular motion (torque) is.
We are learning to apply angular motion to sport specific examples.