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

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3A/3B BIOMECHANICS

Movement principles and concepts
Unit: 3A Scope & Sequence Elaboration The principle of Inertia: Newton’s First Law of motion; mass; contact forces Newton’s first law - Principle of Inertia Define 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 motion Impulse and momentum are related in that a change in momentum results in a proportional change in impulse. muscle structure mechanics of musculo skeletal system muscle characteristics Models for biomechanical analysis. Identify possible models for analysis e.g. Knudsen and Morrison – model for qualitative analysis. Physical Education Studies Elaboration Support Document, 2008

Movement principles and concepts
Unit: 3B Segmental Interaction i.e. Kinematic chain Dynamical Systems Theory Balance Torque Angular Inertia (Rotational Inertia) Centre of Gravity Principle of Spin Bernoulli’s Principle Magnus Effect Fluid forces. surface drag i.e. swim suits skins form drag i.e. golf balls wave drag The 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

STRUCTURE OF SKELETAL MUSCLE
Skeletal Muscle surrounded by Epimysium Made up of bundles of muscle fibres (fascicles) surrounded by Perimysium Each fascicle contains individual muscle fibres, surrounded by Endomysium Fibres 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

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

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

IMPULSE AND SPORT INCREASING MOMENTUM
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

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!

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

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 SHORTENING VELOCITY

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

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

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).

CONSERVATION OF 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

Late boundary layer separation Early boundary layer separation
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

3. FOLLOW THROUGH 2. EXECUTION PHASE
STRIKING 1. PREPARATION Side on position to allow for greater force generation through sequential summation of force 3. FOLLOW THROUGH Follow through towards the target to prevent decceleration of final segment and ensure safe dissipation of force 2. EXECUTION PHASE Movement of big body parts (legs) followed by rotation of hips, shoulders, arms and then wrists Arms fully extend at point of contact to ensure longest possible lever at impact