3A/3B BIOMECHANICS

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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 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.1. muscle structure2. mechanics of musculo skeletal

system3. 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

•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.

Movement principles and concepts

Unit: 3B

Physical Education Studies Elaboration Support Document, 2008

STRUCTURE OF SKELETAL MUSCLE

TIME TIME

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?

IMPULSE – MOMENTUM RELATIONSHIP

• 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

IMPULSE AND ACCURACY

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

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

Wides stance aims to maximise impulse by ↑

contact time, however force generated will be low compared to the hit

IMPULSE AND SPORT

• Because impulse is force * time, we can change either one to suit the demands of the situation

1. 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.

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Large backswing ensures maximum force is applied, but over a short period of

time

IMPULSE AND SPORT

2. 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

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

CONCENTRIC ECCENTRIC

FORCE – VELOCITY

MECHANICAL CHARACTERISTICS OF MUSCLE

LENGTHENING VELOCITY SHORTENING VELOCITY0

During eccentric muscle contraction (lengthening) , max force achieved during

max velocity

During concentric muscle contraction (shortening),

max force achieved during minimum velocity

During isometric contraction, force

generated does not result in change of muscle length

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

FULCRUM

EFFORT FORCE

RESISTANCE FORCE

RESISTANCE ARM

EFFORT ARM

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

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• 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.

ANGULAR MOMENTUM – MOMENT OF INERTIA (rotational inertia)

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

Angular momentum

Moment of inertia

Angular velocity

TIME

Angular velocity high, moment of

inertia low

Angular velocity low, moment of

inertia high

Angular momentum

remains constant

TURBULENT FLOW LAMINAR FLOW

High pressure at front of ball

High pressure at front of ball

Small turbulent pocket (high

pressure) at rear 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

Late boundary layer separation

Early boundary layer separation