CHAPTER 4CHAPTER 4

AN INTRODUCTION TO AN INTRODUCTION TO BIOMECHANICSBIOMECHANICS

BiomechanicsBiomechanics Biomechanics is the study of how and why Biomechanics is the study of how and why

the human body moves. the human body moves. It investigates how the physical laws of It investigates how the physical laws of

mechanics apply to the human body.mechanics apply to the human body. Role of biomechanist: Role of biomechanist: analyse an athletes analyse an athletes

performance in order to improve performance in order to improve technique, improve equipment design and technique, improve equipment design and reduce injuries.reduce injuries.– Quantitative Analysis:Quantitative Analysis: use of numbers (eg use of numbers (eg

speed / distance / time)speed / distance / time)– Qualitative Analysis: Qualitative Analysis: description without description without

numbers (eg bend your kneesnumbers (eg bend your knees Checkpoints: Checkpoints: Page 95 – Q.1,3 Page 95 – Q.1,3

Principles of BiomechanicsPrinciples of Biomechanics CD-ROM:CD-ROM:

– OverviewOverview– InertiaInertia– Mass Mass – ForceForce

Types of forcesTypes of forces

– Newtons Laws of MotionNewtons Laws of Motion Velocity: (page 98)Velocity: (page 98)

– What does velocity measure?What does velocity measure?– What are its two important characteristics?What are its two important characteristics?

Read: Reality PE Snapshots (Page 99)Read: Reality PE Snapshots (Page 99)– Radar equipment!Radar equipment!

Principles (cont)Principles (cont) CD-ROM:CD-ROM:

– ImpulseImpulse Checkpoints: Checkpoints: (page 102)(page 102)

– Questions: 1, 2, 4, 5Questions: 1, 2, 4, 5 Acceleration: (Newton’s 2Acceleration: (Newton’s 2ndnd law) law)

– What is acceleration?What is acceleration?– How do you calculate acceleration?How do you calculate acceleration?

Conservation of momentum: (Newtons 3Conservation of momentum: (Newtons 3rdrd law) law)– What is this principle?What is this principle?– Give an example of how this principle works?Give an example of how this principle works?

Elasticity:Elasticity:– What does the term elasticity mean? Explain two ways in What does the term elasticity mean? Explain two ways in

which a tennis player can generate more velocity which a tennis player can generate more velocity through elasticity.through elasticity.

Principles (cont)Principles (cont) Summation of Momentum:Summation of Momentum:

– Define summation of momentum?Define summation of momentum?– When does effective summation of When does effective summation of

momentum take place?momentum take place? CD-ROM:CD-ROM:

– FrictionFriction Checkpoints: Checkpoints: (page 112)(page 112)

– Questions 3, 5, 6Questions 3, 5, 6

Balance and StabilityBalance and Stability Read pages 113-118Read pages 113-118 Define the terms Balance and Stability?Define the terms Balance and Stability? What factors affect balance and stability?What factors affect balance and stability? Explain the difference between static and Explain the difference between static and

dynamic balances?dynamic balances? What is meant by the ‘centre of gravity’ and What is meant by the ‘centre of gravity’ and

how does it change when you change your how does it change when you change your body position?body position?

How does the mass of a person affect their How does the mass of a person affect their stability?stability?

CD-ROM: CD-ROM: Recap of balance using CD Recap of balance using CD examples.examples.

Basic movement patternsBasic movement patterns

Striking Throwing

StoppingRunning

Basic movement patternsBasic movement patterns

StrikingStriking ThrowingThrowing RunningRunning StoppingStopping

TennisTennisGolfGolfVolleybalVolleyballlllCricketCricket

BaseballBaseballBasketbaBasketballllNetballNetballAthleticsAthletics

AthleticAthleticssBasebalBaseballlCricketCricketSoccerSoccer

BaseballBaseballNetballNetballAthleticsAthleticsCyclingCycling

Biomechanical principles associated Biomechanical principles associated with basic movement patternswith basic movement patterns

Striking - Striking - GolfGolf

Throwing - Throwing - BaseballBaseball

Running - Running - AthleticsAthletics

Stopping - Stopping - NetballNetball

Newtons Newtons laws (force)laws (force)leversleversmomentummomentumimpactimpactstabilitystability

projectile projectile motionmotionflattening flattening the arcthe arcsummation summation of of momentummomentumaccuracyaccuracy

forces forces (action/ (action/ reaction)reaction)motion motion (straight (straight line)line)momentumomentummfrictionfriction

forcesforcesacceleratioacceleration and n and decelerationdecelerationNewtons Newtons lawslawsfrictionfriction

Tennis

Biomechanical principles Biomechanical principles associated with tennisassociated with tennis

ForcesForces LeversLevers TorqueTorque VelocityVelocity PowerPower AccelerationAcceleration DecelerationDeceleration Projectile motionProjectile motion MomentumMomentum ElasticityElasticity

Coefficient of restitutionCoefficient of restitution

SpinSpin Centre of gravityCentre of gravity Base of supportBase of support AccuracyAccuracy MassMass InertiaInertia MotionMotion ImpulseImpulse

TennisTennis

Force (Newtons N)Force (Newtons N)– A push or a pullA push or a pull– What effect does a force have on an What effect does a force have on an

object?object?

Starts, stops, speeds up, slows Starts, stops, speeds up, slows down, down, changes direction. It changes changes direction. It changes an objects velocityan objects velocity

Velocity (msVelocity (ms-1-1))– displacement / timedisplacement / time

Mass (kg)Mass (kg)– Amount of matter in an objectAmount of matter in an object– Weight is an indirect measure of massWeight is an indirect measure of mass

Acceleration (msAcceleration (ms-2-2))

- change in velocity / time- change in velocity / time

- - final velocity – initial velocityfinal velocity – initial velocity

timetime

Newtons lawsNewtons laws

1.1. A body continues in its state of rest A body continues in its state of rest or of or of uniform motion in a straight line uniform motion in a straight line unless it is unless it is compelled to change that compelled to change that state by forces state by forces acting on it.acting on it.

2.2. The acceleration of an object is The acceleration of an object is directly directly proportional to the net force proportional to the net force applied and applied and inversely proportional to its inversely proportional to its mass.mass.

F = maF = ma3.3. For every action the is an equal and For every action the is an equal and

oppositeopposite reaction.reaction.

MomentumMomentum

Momentum (kg msMomentum (kg ms-1)-1)

- p = mv - p = mv - two objects travelling at the same - two objects travelling at the same velocity, the one with the greater velocity, the one with the greater mass will have the greater momentum mass will have the greater momentum and vice versa, two objects of the and vice versa, two objects of the same mass, the one travelling at a same mass, the one travelling at a greater velocity will have a greater greater velocity will have a greater momentum.momentum.- momentum is always conserved- momentum is always conserved

Impulse Impulse – Change in momentumChange in momentum– I = I = p OR I = Ft p OR I = Ft – Impulse can be increased by increasing Impulse can be increased by increasing

the force applied or increasing the time the force applied or increasing the time over which the force is applied.over which the force is applied.

– When a mass is constant, a change in When a mass is constant, a change in impulse will result in a greater release impulse will result in a greater release velocity of the object (ball)velocity of the object (ball)

Summation of momentumSummation of momentum– Used to maximise the speed of the Used to maximise the speed of the

racquet headracquet head– Works when the larger slower body Works when the larger slower body

parts begin the movement and move parts begin the movement and move sequentially through until the smaller sequentially through until the smaller and quicker finish the movement.and quicker finish the movement.

– See laboratorySee laboratory

ElasticityElasticity– The ability of an object to return to its The ability of an object to return to its

original shapeoriginal shape– The more quickly an object does this the The more quickly an object does this the

less energy it loosesless energy it looses– Coefficient of restitution is a measure of Coefficient of restitution is a measure of

an objects elasticityan objects elasticity

e = e = height bouncedheight bounced

height droppedheight dropped– String tension determines how much String tension determines how much

contact time the ball has with the contact time the ball has with the racquetracquet

LeversLevers– Classes of leversClasses of levers– Factors that affect the use of external Factors that affect the use of external

leverslevers Length of leversLength of levers Inertia of the leverInertia of the lever ForceForce

Compare and contrast techniques Compare and contrast techniques (elite and novice)(elite and novice)

Evaluate performance using Evaluate performance using biomechanical principlesbiomechanical principles