2 Movement principles and concepts Unit: 3AScope & SequenceElaborationThe principle of Inertia: Newton’s First Law of motion; mass; contact forcesNewton’s first law - Principle of InertiaDefine the term vector. Relate to movement principles.The principle of Force-Time: muscle structure; mechanics of the musculo-skeletal system; mechanical characteristics of muscle (force-velocity; force-length; force-time); Newton’s Second Law of Motion. impulse – momentum relationship.2nd Law of motionImpulse and momentum are related in that a change in momentum results in a proportional change in impulse.muscle structuremechanics of musculo skeletal systemmuscle characteristicsModels for biomechanical analysis.Identify possible models for analysise.g. Knudsen and Morrison – model for qualitative analysis.Physical Education Studies Elaboration Support Document, 2008
3 Movement principles and concepts Unit: 3BSegmental Interaction i.e. Kinematic chainDynamical Systems TheoryBalanceTorqueAngular Inertia (Rotational Inertia)Centre of GravityPrinciple of SpinBernoulli’s PrincipleMagnus EffectFluid forces.surface drag i.e. swim suits skinsform drag i.e. golf ballswave dragThe principle of Balance: torque (moment of force); angular inertia (moment of inertia); equilibrium; centre of gravity.The principle of Spin: fluids; fluid forces (buoyancy, drag, lift-Bernoulli’s Principle, the Magnus effect).The principle of Segmental Interaction: kinematic chain; corrections in body positioning and timing; dynamical systems theory.Physical Education Studies Elaboration Support Document, 2008
4 STRUCTURE OF SKELETAL MUSCLE Skeletal Muscle surrounded by EpimysiumMade up of bundles of muscle fibres (fascicles) surrounded by PerimysiumEach fascicle contains individual muscle fibres, surrounded by EndomysiumFibres arranged into myofibrils, running parallel to each other & the length of the muscle fibre.Myofibrils contain a chain of sarcomeres, which are composed of actin and myosin filaments responsible for creating movement
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?FORCEFORCETIMETIME
6 IMPULSE AND ACCURACY FLATTENING THE SWING ARC Good technique can↑ contact time with a ball during collision sportsMay provide opportunity for ↑ force application in desired direction (hockey drag flick)May also provide ↑ accuracy, however usually occurs with a ↓ in force applicationA more curved arc reduces the likelihood of a successful outcome by reducing the opportunity for application of force in the intended direction of travelFlattening 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 INCREASING MOMENTUM Because impulse is force * time, we can change either one to suit the demands of the situationINCREASING MOMENTUMIn 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 momentumIdeally 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 timeWides stance aims to maximise impulse by ↑ contact time, however force generated will be low compared to the hit
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 timeWould 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 – VELOCITYMuscle can create ↑ force with a ↓ velocity of concentric contractionMuscle can resist ↑ force with a ↑ velocity of eccentric contractionCONCENTRICECCENTRICIts 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 – VELOCITYDuring isometric contraction, force generated does not result in change of muscle lengthDuring concentric muscle contraction (shortening), max force achieved during minimum velocityFORCEDuring eccentric muscle contraction (lengthening) , max force achieved during max velocityLENGTHENING VELOCITYSHORTENING 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 leverOutput (Resistance) Force – Force exerted BY the leverRESISTANCE FORCEEFFORT FORCEEFFORT ARMRESISTANCE ARMFULCRUM
12 LEVERS - PRINCIPLES Velocity is greatest at the distal end of a lever Longer the lever, greater the velocity at impactE.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
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 Moment of inertiaAngular velocity high, moment of inertia lowAngular velocity low, moment of inertia highAngular velocityAngular momentum remains constantTIME
15 Late boundary layer separation Early boundary layer separation TURBULENT FLOWLAMINAR FLOWLate boundary layer separationEarly boundary layer separationHigh pressure at front of ballSmall turbulent pocket (high pressure) at rear of ballHigh pressure at front of ballLarge turbulent pocket (low pressure) at rear of ballTurbulent 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 ballLaminar 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
16 3. FOLLOW THROUGH 2. EXECUTION PHASE STRIKING1. PREPARATIONSide on position to allow for greater force generation through sequential summation of force3. FOLLOW THROUGHFollow through towards the target to prevent decceleration of final segment and ensure safe dissipation of force2. EXECUTION PHASEMovement of big body parts (legs) followed by rotation of hips, shoulders, arms and then wristsArms fully extend at point of contact to ensure longest possible lever at impact