Biomechanics Biomechanics The study of cause and effectThe study of cause and effect

FORM 6 PEDFORM 6 PED

Why study Biomechanics?Why study Biomechanics? To understand To understand howhow people can move. people can move.

1. To 1. To enhance enhance skill performanceskill performance elite athleteselite athletes physical challengesphysical challenges

Why study Biomechanics?Why study Biomechanics?

2. 2. To To lower the risk for lower the risk for injuryinjury Exercise equipment & techniqueExercise equipment & technique shoes & surfacesshoes & surfaces braces & orthoticsbraces & orthotics AutomobilesAutomobiles collisionscollisions

Why study Biomechanics?Why study Biomechanics?

Can a cow really jump over the moon?

Define a ForceDefine a Force

1.1. Forces and LeversForces and Levers

A A forceforce is a push or pull. is a push or pull.

When a force acts upon a body (object) it can When a force acts upon a body (object) it can produce 3 types of movement.produce 3 types of movement.

TranslationTranslation – Moves from A to B. – Moves from A to B.

e.g. A golf shot starts on the tee and finishes e.g. A golf shot starts on the tee and finishes on the fairway.on the fairway.

RotationRotation – If force not applied through the centre – If force not applied through the centre of gravity the object will rotate e.g. putting spin of gravity the object will rotate e.g. putting spin on a volleyball serve.on a volleyball serve.

DeformationDeformation – The object loses shape on – The object loses shape on impact e.g. a squash ball being hitimpact e.g. a squash ball being hit

The main force acting on all parts of the body is The main force acting on all parts of the body is gravitygravity..

Centre of gravityCentre of gravity (COG) can therefore be defined as the (COG) can therefore be defined as the point at which all parts of the body are in balance.point at which all parts of the body are in balance.

In men, the COG is about 57% of standing height, in In men, the COG is about 57% of standing height, in women 55%. Women have more mass concentrated women 55%. Women have more mass concentrated around the hips and below and this gives them an around the hips and below and this gives them an advantage in balance related activities.advantage in balance related activities.

When we produce rotation as a consequence of a force When we produce rotation as a consequence of a force being applied, the body rotates about the COG.being applied, the body rotates about the COG.

These are known as the AXIS OF ROTATION

The body rotates around The body rotates around three different axes.three different axes.

1.1. LongitudinalLongitudinal

E.g. Pirouette in E.g. Pirouette in dance, twist in dance, twist in diving, spinning in diving, spinning in ice skatingice skating

2. Transverse2. Transverse

e.g. forward / backward e.g. forward / backward roll/ somersaultroll/ somersault

3. Sagital3. Sagital

e.g. cartwheel, cricket e.g. cartwheel, cricket delivery, delivery,

LeversLevers A lever is basically a rigid structure, hinged at A lever is basically a rigid structure, hinged at

some part and to which forces are applied at some part and to which forces are applied at two other points.two other points.

Levers consists of three parts.Levers consists of three parts.1.1. ResistanceResistance2.2. EffortEffort3.3. Falcrum or pivotFalcrum or pivot

The point of support, or axis, about which a lever The point of support, or axis, about which a lever may be made to rotatemay be made to rotate

FUNCTIONS OF A LEVERFUNCTIONS OF A LEVER

Levers perform two main functions:Levers perform two main functions:

1.1. To increase the resistance that can be moved To increase the resistance that can be moved with a given effort, eg. Crowbar.with a given effort, eg. Crowbar.

2.2. To increase the velocity at which an object To increase the velocity at which an object will move with a given force, eg. Golf clubwill move with a given force, eg. Golf club

There are three classes of lever.There are three classes of lever.

Levers-First ClassLevers-First Class In a first class lever In a first class lever

the fulcrum is in the the fulcrum is in the middle and the load middle and the load and effort is on either and effort is on either sideside

Think of a see-sawThink of a see-saw

Levers-Second ClassLevers-Second Class In a second class In a second class

lever the fulcrum is at lever the fulcrum is at the end, with the load the end, with the load in the middlein the middle

Think of a Think of a wheelbarrowwheelbarrow

Levers-Third ClassLevers-Third Class In a third class lever In a third class lever

the fulcrum is again the fulcrum is again at the end, but the at the end, but the effort is in the middleeffort is in the middle

Think of a pair of Think of a pair of tweezerstweezers

Newton’s Laws of MotionNewton’s Laws of Motion

Sir Isaac Newton (1642-Sir Isaac Newton (1642-1727) developed 3 laws 1727) developed 3 laws to explain relationship to explain relationship between the forces between the forces acting on a body and the acting on a body and the motion of a body.motion of a body.

Law 1Law 1 ““An object at rest An object at rest

tends to remain at tends to remain at rest unless acted rest unless acted upon by some upon by some external force”external force”

This is known as This is known as Inertia. High level of Inertia. High level of inertia can be inertia can be advantageous and advantageous and disadvantageous in disadvantageous in different sports.different sports.

Law 2Law 2 “ “When a force acts upon a When a force acts upon a

mass, the result is mass, the result is acceleration of that mass”acceleration of that mass”

The greater the force, the The greater the force, the greater the accelerationgreater the acceleration

The smaller the mass, the The smaller the mass, the greater the accelerationgreater the acceleration

The mass will accelerate in the The mass will accelerate in the direction the force is applieddirection the force is applied

Force = mass x accelerationForce = mass x acceleration

(F=MA)(F=MA)

Law 3Law 3

“ “For every action, For every action, there is an equal there is an equal and opposite and opposite reaction”reaction”

These 2 forces These 2 forces alwaysalways work in pairswork in pairs

1.1. action forceaction force2.2. reaction forcereaction force

The big question..The big question..

Analysing the Overhead Analysing the Overhead Serve in VolleyballServe in Volleyball

Try analysing the volleyball serve.Try analysing the volleyball serve.

Ask yourself “ How is the biomechanical Ask yourself “ How is the biomechanical principle – Newton’s Laws of Motion principle – Newton’s Laws of Motion being applied to the overhead serve in being applied to the overhead serve in volleyball? Where can I see this being volleyball? Where can I see this being applied?applied?

This will help you to explain how they This will help you to explain how they contribute to the performance of the contribute to the performance of the serve.serve.

Principles of Balance and Principles of Balance and StabilityStability

StabilityStabilityStability is defined as the ability to hold or Stability is defined as the ability to hold or

maintain a position in space.maintain a position in space.

StabilityStabilityThe two main elements in maintaining stability The two main elements in maintaining stability

are:are:1.1. The position of the COG with respect to the The position of the COG with respect to the

base of support.base of support.2.2. The direction of the forces involved.The direction of the forces involved.

Principle 1Principle 1

The closer the line of gravity is to the The closer the line of gravity is to the centre of the base of support, the greater centre of the base of support, the greater the probability of maintaining balance.the probability of maintaining balance.

Principle 2Principle 2

The broader the base of The broader the base of support, the greater support, the greater the probability of the probability of maintaining balance.maintaining balance.

Principle 3Principle 3

The probability of The probability of maintaining balance maintaining balance is increased when is increased when the COG is lowered the COG is lowered in relation to the in relation to the base of support. base of support.

Principle 4Principle 4

The further the body part moves The further the body part moves away from the line of gravity, the away from the line of gravity, the probability of maintaining probability of maintaining balance decreases unless balance decreases unless another body part moves to another body part moves to compensate for it.compensate for it.

Types of MotionTypes of Motion

There are 4 main types of motion;There are 4 main types of motion;

A) Linear MotionA) Linear Motion

When parts of the When parts of the body move in body move in straight parallel straight parallel lines. Quite rare in lines. Quite rare in sporting situations.sporting situations.

e.g. tobogganing down e.g. tobogganing down a hill, dropping a a hill, dropping a ball, sliding into first ball, sliding into first basebase

B) Curvilinear MotionB) Curvilinear Motion

When points in the When points in the body move in curved body move in curved parallel lines.parallel lines.

e.g. free fall skydiving, e.g. free fall skydiving, path of an arrowpath of an arrow

If the path of two points on a body follow straight parallel lines, the motion is linear. If the path is curved, the motion is curvilinear.

C) Angular MotionC) Angular Motion

Rotation about an axis that can be Rotation about an axis that can be internal (axis inside the body) or external internal (axis inside the body) or external (axis outside the body). E.g. swinging on (axis outside the body). E.g. swinging on a high bar, a forward roll, hammer a high bar, a forward roll, hammer throwing, pole vault over bar, softball throwing, pole vault over bar, softball pitch, fosbury flop.pitch, fosbury flop.

D) General MotionD) General Motion

Linear motion of the Linear motion of the body as a result of body as a result of angular motion of angular motion of other parts of the other parts of the body.body.

e.g. cycling, e.g. cycling, swimming, using a swimming, using a wheelchairwheelchair

Torque ?Torque ?Torque is a Torque is a turningturning force. force.

Eccentric force produces spin.Eccentric force produces spin.

It depends on how far the mass is It depends on how far the mass is from the axis and the size of the from the axis and the size of the mass. mass.

How do we produce topspin or How do we produce topspin or backspin ?backspin ?

Where do we hit the ball ?Where do we hit the ball ?

How can we generate more spin ?How can we generate more spin ?

MomentumMomentum

Momentum is moving inertiaMomentum is moving inertia. We can rewrite . We can rewrite Newton’s 1Newton’s 1stst law to include momentum. law to include momentum.

“ “An object that is moving will continue to move in An object that is moving will continue to move in the direction the force was applied until another the direction the force was applied until another force is applied”force is applied”

The greater the momentum the greater the force The greater the momentum the greater the force required to stop it e.g. small /large snowball.required to stop it e.g. small /large snowball.

Momentum (kgms) = mass (kg) x velocity (ms)Momentum (kgms) = mass (kg) x velocity (ms)

Momentum can act when an object is Momentum can act when an object is translatingtranslating. This is . This is linear momentumlinear momentum..

Momentum can act on an object when it Momentum can act on an object when it is is rotatingrotating. This is . This is angular momentumangular momentum..

Conservation of Conservation of MomentumMomentumWhen objects collide, momentum is When objects collide, momentum is

conserved throughout. conserved throughout.

Momentum before impact = momentum after Momentum before impact = momentum after impact.impact.

MOMENTUM = MASS X VELOCITY kgms kg ms

Use the information on Conservation of Momentum and steps below to Use the information on Conservation of Momentum and steps below to calculate the speed of the golf ball after impact.calculate the speed of the golf ball after impact.

A A golfer swings a 0.35kg club at 30m/s to hit a 0.004kg golf ball off the tee. golfer swings a 0.35kg club at 30m/s to hit a 0.004kg golf ball off the tee. After impact his club speed drops to 25m/s.After impact his club speed drops to 25m/s.

Remember Remember

Momentum before impact = Momentum after impact.Momentum before impact = Momentum after impact. (M = m x v) (M = m x v)

Club MomentumClub Momentum Ball MomentumBall Momentum Total MomentumTotal Momentum

Club MomentumClub Momentum Ball MomentumBall Momentum Total MomentumTotal Momentum

Before Impact

After Impact

What is the Ball Velocity?What is the Ball Velocity?

Momentum = mass x velocityMomentum = mass x velocity

Velocity = Velocity = momentummomentum

massmass

Use the information on Conservation of Momentum and steps below to Use the information on Conservation of Momentum and steps below to calculate the speed of the hockey stick after impact.calculate the speed of the hockey stick after impact.

A A ice hockey player uses their stick to strike a 500 gram (0.5kg) puck ice hockey player uses their stick to strike a 500 gram (0.5kg) puck moving at 2m/s toward their opponent’s goal. The stick has a mass of moving at 2m/s toward their opponent’s goal. The stick has a mass of 2kg and possesses stick head velocity of 25m/s before impact. After 2kg and possesses stick head velocity of 25m/s before impact. After impact, the stick head velocity decreases to 17m/s. impact, the stick head velocity decreases to 17m/s.

Remember Remember

Momentum before impact = Momentum after impact.Momentum before impact = Momentum after impact. (M = m x v) (M = m x v)

Stick MomentumStick Momentum Puck MomentumPuck Momentum Total MomentumTotal Momentum

Stick MomentumStick Momentum Puck MomentumPuck Momentum Total MomentumTotal Momentum

Before Impact

After Impact