3A/3B BIOMECHANICS

1. 3A/3B BIOMECHANICS www.flickr.com/photos/8136496@N05/2562423599

2. Physical Education Studies Elaboration Support Document, 2008

3. Physical Education Studies Elaboration Support Document, 2008

4. STRUCTURE OF SKELETAL MUSCLE

5. IMPULSE – MOMENTUM RELATIONSHIP Which method would you prefer to use when catching a ball – a large force over a short period of time or a smaller peak force over a longer period of time? FORCE FORCE TIME TIME

6. IMPULSE AND ACCURACY • FLATTENING THE SWING ARC • Good technique can↑ contact time with a ball during collision sports • May provide opportunity for ↑ force application in desired direction (hockey drag flick) • May also provide ↑ accuracy, however usually occurs with a ↓ in force application A more curved arc reduces the likelihood of a successful outcome by reducing the opportunity for application of force in the intended direction of travel Flattening the arc increases the likelihood of application of force to object in desired direction of travel by creating a zone of flat line motion

7. IMPULSE AND SPORT • Because impulse is force * time, we can change either one to suit the demands of the situation • INCREASING MOMENTUM • In hockey a hit will place a large force, but over a small time. A drag flick would use a smaller force over a longer period of time. Either way the ball will increase its momentum • Ideally we look to maximise both force and time, however the human body rarely allows for this to happen. Large backswing ensures maximum force is applied, but over a short period of time Wides stance aims to maximise impulse by ↑ contact time, however force generated will be low compared to the hit www.flickr.com/photos/mark_fletcher/2325626998/sizes/s/ www.flickr.com/photos/stephanderson/2190910716

8. IMPULSE AND SPORT • DECREASING MOMENTUM • A cricket ball is hit towards a fielder. The fielder wishes to stop the ball (take momentum back to zero). • Would he apply a large force over a short period of time • Would he apply a small force over a longer period of time. • Which method is likely to be more successful in catching the ball? • Therefore in stopping a force we usually increase the time component so we can reduce the peak force!

9. MECHANICAL CHARACTERISTICS OF MUSCLE FORCE – VELOCITY • Muscle can create ↑ force with a ↓ velocity of concentric contraction • Muscle can resist ↑ force with a ↑ velocity of eccentric contraction CONCENTRIC ECCENTRIC Its easier to lift a heavy weight concentrically (upwards) slowly than it is quickly! Its easier to resist a heavy weight eccentrically (lowering) quickly rather than slowly

10. MECHANICAL CHARACTERISTICS OF MUSCLE FORCE – VELOCITY During isometric contraction, force generated does not result in change of muscle length During concentric muscle contraction (shortening), max force achieved during minimum velocity FORCE During eccentric muscle contraction (lengthening) , max force achieved during max velocity LENGTHENING VELOCITY 0 SHORTENING VELOCITY

11. LEVERS - ANATOMY • Fulcrum– point around which the lever rotates • Effort Arm – The part of the lever that the effort force is applied to (measured from the fulcrum to the point at which the force is applied) • Resistance Arm – The part of the lever that applies the resistance force (measured from the fulcrum to the center of the resistance force) • Input (Effort) Force – Force exerted ON the lever • Output (Resistance) Force – Force exerted BY the lever RESISTANCE FORCE EFFORT FORCE EFFORT ARM RESISTANCE ARM FULCRUM

12. LEVERS - PRINCIPLES • Velocity is greatest at the distal end of a lever • Longer the lever, greater the velocity at impact • E.g. Golf driver vs. 9 iron • ↑ club length creates ↑ velocity and momentum at impact provided the athlete can control the longer lever – longer generally means↑ mass! • Children often have difficulty with this and subsequently use shorter levers to gain better control – shorter cricket bat, tennis racquet etc www.flickr.com/photos/flash716/2578346899/ www.flickr.com/photos/cwalker71/2455913000/

13. ANGULAR MOMENTUM – MOMENT OF INERTIA (rotational inertia) • If the body’s mass is close to the axis of rotation, rotation is easier to manipulate. This makes the moment of inertia smaller and results in an increase in angular velocity. • Moving the mass away from the axis of rotation slows down angular velocity. Try this on a swivel chair – see which method will allow you to spin at a faster rate? Note what happens when you move from a tucked position (left) to a more open position (right).

14. CONSERVATION OF ANGULAR MOMENTUM Angular momentum Moment of inertia Angular velocity high, moment of inertia low Angular velocity low, moment of inertia high Angular velocity Angular momentum remains constant TIME

15. TURBULENT FLOW LAMINAR FLOW Late boundary layer separation Early boundary layer separation High pressure at front of ball Small turbulent pocket (high pressure) at rear of ball High pressure at front of ball Large turbulent pocket (low pressure) at rear of ball Turbulent flow causes the boundary layer separation to take place later. This causes a smaller pressure differential between the front and back of the ball as their is only a small pocket of turbulent wake at the rear of the ball Laminar flow causes the boundary layer separation to take place earlier. This causes a larger pressure differential between the front and rear of the ball as their is now a large pocket of turbulent wake at the back of the ball