Biomechanical Definitions Chapter 4

Biomechanical Biomechanical DefinitionsDefinitions

Chapter 4Chapter 4

FORCEFORCE

Force is the Force is the “push”“push” or or “pull”“pull” placed upon placed upon an object to:an object to:

Get it movingGet it moving Speed it upSpeed it up Slow it downSlow it down Stop itStop it Change it’s directionChange it’s direction

FORCE (continued…)FORCE (continued…)

Force is used to change the velocity of Force is used to change the velocity of something.something.

InternallyInternally, force is produced by muscle , force is produced by muscle contractionscontractions

ExternallyExternally, force is generated by gravity, , force is generated by gravity, friction, water and airfriction, water and air

FORCE (continued…)FORCE (continued…)

Force =Force = Strength or power applied to change the Strength or power applied to change the body’s state of motionbody’s state of motion

Examples:Examples:

1.1. ______________________________________________________

2.2. ______________________________________________________

3.3. ______________________________________________________

INERTIAINERTIA

InertiaInertia is the tendency of an object to is the tendency of an object to maintain it’s state of motionmaintain it’s state of motion (velocity), (velocity), whether it is stationary or movingwhether it is stationary or moving

The The inertiainertia of an object is of an object is directly related directly related to it’s mass-to it’s mass- (it is harder to move an object (it is harder to move an object made up of more matter!!!)made up of more matter!!!)

INERTIAINERTIA

To alter an object’s To alter an object’s motionmotion we must apply we must apply an an unbalanced forceunbalanced force to overcome it’s to overcome it’s inertiainertia

The The force may alter an object’s speedforce may alter an object’s speed and/ and/ or or direction of movementdirection of movement

E.g: A Spike in beach volleyballE.g: A Spike in beach volleyball

MASS & WEIGHTMASS & WEIGHT

MassMass is the is the amount of matteramount of matter that makes up an that makes up an objectobject

Eg: Eg: 1kg of 1kg of feathers vs feathers vs 1kg of bricks 1kg of bricks

WeightWeight is the is the force exerted by force exerted by the earth’s the earth’s gravitygravity on an on an objectobject

VELOCITYVELOCITY

Velocity =Velocity = distancedistance

timetime Velocity measures the Velocity measures the speed of an objectspeed of an object

There are 2 main characteristics of velocity:There are 2 main characteristics of velocity:

1.1. Speed (how quickly it covers the ground)Speed (how quickly it covers the ground)

2.2. DirectionDirection

VELOCITYVELOCITY

The The unit of measurementunit of measurement we use for velocity is: we use for velocity is:

*Metres per second (m / s)*Metres per second (m / s)

A stationary object is said to have a velocity of A stationary object is said to have a velocity of zerozero

An object travelling 5 metres each second has a An object travelling 5 metres each second has a velocity of = velocity of =

________________________________________________________

MOMENTUMMOMENTUM

MomentumMomentum is the is the measure of the measure of the amount of motionamount of motion possessed by a possessed by a moving bodymoving body

(mass x velocity)(mass x velocity)

The The units of units of measurementmeasurement we use we use for momentum are for momentum are kilograms and metres kilograms and metres per second per second

(kg & m/s)(kg & m/s)

MOMENTUMMOMENTUM

The momentum of an The momentum of an object is directly object is directly

related to it’s related to it’s massmass and and it’s it’s velocityvelocity

MOMENTUMMOMENTUM

1. “If 2 objects of 1. “If 2 objects of different massdifferent mass are moving with the are moving with the same velocitysame velocity it will be it will be harderharder to stop the object with to stop the object with the the greater mass”greater mass”

Eg: Eg: St. Kilda AFL footballersSt. Kilda AFL footballers Fraser Gehrig (110kg) vs Stephen Milne (83kg)Fraser Gehrig (110kg) vs Stephen Milne (83kg)

2. “If 2 objects of identical mass are moving at different 2. “If 2 objects of identical mass are moving at different velocities it will be harder to stop the object moving at velocities it will be harder to stop the object moving at a greater velocity”a greater velocity”

Eg:Eg: A tennis serve A tennis serve Andy Roddick vs Maria SharapovaAndy Roddick vs Maria Sharapova

MOMENTUMMOMENTUM

When two bodies When two bodies collidecollide, the one that , the one that possesses the possesses the most momentummost momentum will be will be least effectedleast effected

Therefore:Therefore:

On a rugby field a smaller, faster moving On a rugby field a smaller, faster moving player knocks over a bigger, slower player.player knocks over a bigger, slower player.

The smaller player has more momentum The smaller player has more momentum due to extra speed on the fielddue to extra speed on the field

MOMENTUMMOMENTUM

Weight = 90kgWeight = 90kgVelocity = 1.8m/sVelocity = 1.8m/s

Weight = 120kgWeight = 120kgVelocity = 1.2m/sVelocity = 1.2m/s

MOMENTUMMOMENTUM

Momentum = MASS x Momentum = MASS x VELOCITY VELOCITY

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IMPULSEIMPULSE

The The application of forceapplication of force over a period of over a period of time which time which changes the velocitychanges the velocity (speed)(speed) of a body or objectof a body or object

**The **The larger the impulselarger the impulse applied, the applied, the greater greater the changethe change in in momentummomentum

Eg: The spin before a discus is thrown. This Eg: The spin before a discus is thrown. This technique increases the technique increases the timetime over which over which

force is appliedforce is applied

ACCELERATIONACCELERATION

Acceleration = The Acceleration = The rate of changerate of change in in velocityvelocity

It is how quickly an object can It is how quickly an object can change change velocity when an unbalanced force velocity when an unbalanced force causes movement.causes movement.

**Newton’s 2**Newton’s 2ndnd law of motion explains law of motion explains this principle.this principle.

ACCELERATIONACCELERATION

Two identical shot puts are acted on by an Two identical shot puts are acted on by an unbalanced force ( they are thrown), unbalanced force ( they are thrown),

One is thrown by an One is thrown by an Olympic athleteOlympic athlete The other is thrown by a The other is thrown by a BeginnerBeginner

Result:Result: The shot put thrown with greater The shot put thrown with greater force (Olympic athlete) will have greater force (Olympic athlete) will have greater accelerationacceleration

ACCELERATIONACCELERATION

** Acceleration is ** Acceleration is measured in measured in metres metres per second squaredper second squared

M / SM / S²²

““Acceleration is directly Acceleration is directly affected by affected by

force….the force….the greater greater the forcethe force used, the used, the

greater the greater the accelerationacceleration””

More force = More force =

More AccelerationMore Acceleration

ACCELERATIONACCELERATION

Mass also affects the acceleration of an object.Mass also affects the acceleration of an object.

For Example-For Example-

If the force applied to two balls is If the force applied to two balls is the samethe same (a (a tennis serve), the ball with a tennis serve), the ball with a smaller masssmaller mass will will have a have a greater accelerationgreater acceleration

VsVs

Acceleration is important at the start of a Acceleration is important at the start of a lot of sporting events, especially sprinting.lot of sporting events, especially sprinting.

Sprint cyclists can accelerate to 16km/ph Sprint cyclists can accelerate to 16km/ph in one second !!!in one second !!!

Because this type of acceleration requires huge amounts Because this type of acceleration requires huge amounts of force, sprint/ power athletes have a lot more muscle of force, sprint/ power athletes have a lot more muscle than long- distance/ endurance athletesthan long- distance/ endurance athletes

ACCELERATIONACCELERATION

ACCELERATIONACCELERATION

Acceleration Acceleration can’t lastcan’t last for the duration of an for the duration of an event…..even a sprint !!!event…..even a sprint !!!

In a In a 100m sprint100m sprint the runners the runners accelerateaccelerate out of the out of the blocks blocks (positive acceleration)(positive acceleration) until they reach until they reach max speedmax speed. At this speed there is no change in . At this speed there is no change in the the rate of velocityrate of velocity (zero acceleration)(zero acceleration) until they until they begin to slow down at the end of the sprint begin to slow down at the end of the sprint (negative acceleration)(negative acceleration)

CONSERVATION OF CONSERVATION OF MOMENTUMMOMENTUM

This principle applies This principle applies to any collision between to any collision between two objects.two objects.

Eg: A foot contacting the ground in running, a Eg: A foot contacting the ground in running, a bat hitting a ball or two balls colliding (pool / bat hitting a ball or two balls colliding (pool / billiards).billiards).

** When a collision occurs: the total momentum of ** When a collision occurs: the total momentum of two bodies two bodies before impactbefore impact is is equalequal to the total to the total momentum momentum after impactafter impact

CONSERVATION OF CONSERVATION OF MOMENTUMMOMENTUM

This is best explained by Newton’s 3This is best explained by Newton’s 3rdrd Law: Law:““For every For every actionaction, there is an , there is an equalequal and and oppositeopposite

reactionreaction””

For example, when playing pool the white ball hits For example, when playing pool the white ball hits a coloured ball and a coloured ball and stops on impactstops on impact. The . The momentummomentum passespasses onto the coloured ball which onto the coloured ball which then moves.then moves.

CONSERVATION OF CONSERVATION OF MOMENTUMMOMENTUM

Basically explained:Basically explained: when the white ball when the white ball applies a forceapplies a force to the next ball, that other to the next ball, that other ball will ball will react with the same forcereact with the same force inin another directionanother direction..

Another Example = 10 Pin BowlingAnother Example = 10 Pin Bowling

Ball hits the pins….pins go flying…!Ball hits the pins….pins go flying…!

ELASTICITYELASTICITY

Elasticity =Elasticity = the ability of surfaces to the ability of surfaces to “give”“give” then returnthen return to their original to their original shape shape

Surfaces with more elasticity result in less energy Surfaces with more elasticity result in less energy being lost on impact because they rebound to being lost on impact because they rebound to their original position quicker.their original position quicker.

Eg: A tennis ball will bounce higher from a surface Eg: A tennis ball will bounce higher from a surface such as ‘rebound ace’ than a grass tennis courtsuch as ‘rebound ace’ than a grass tennis court

ELASTICITYELASTICITY

Rebound Ace (Australian Tennis Open) is more elastic than a Grass Rebound Ace (Australian Tennis Open) is more elastic than a Grass Court (Wimbledon).Court (Wimbledon).

A new tennis ball has A new tennis ball has greater elasticitygreater elasticity than a than a soft, flat one and therefore it will soft, flat one and therefore it will bounce higherbounce higher and and return to shape quickerreturn to shape quicker..

This is advantageous to a tennis player because This is advantageous to a tennis player because they can they can generate more velocitygenerate more velocity when the when the racquet and ball collide.racquet and ball collide.

ELASTICITYELASTICITY

The The temperaturetemperature of the ball can also affect of the ball can also affect it’s elasticity. The it’s elasticity. The hotterhotter a ball is, a ball is, the the more elasticitymore elasticity it will have. it will have.

Eg: Squash players rub the ball between Eg: Squash players rub the ball between their foot and the court before they serve their foot and the court before they serve to heat up the ball. It can then be hit to heat up the ball. It can then be hit harder.harder.

DRAGDRAG

Drag = Disturbed air that creates a Drag = Disturbed air that creates a resistance force opposing the resistance force opposing the movement of a projectile through movement of a projectile through the air the air

Eg: How a tennis ball has more drag than a Eg: How a tennis ball has more drag than a

cricket ball due to the fur on it’s surface cricket ball due to the fur on it’s surface

NEWTON’S LAWSNEWTON’S LAWS

Newton has 3 laws of motion:Newton has 3 laws of motion:

1.1. Law of InertiaLaw of Inertia

2.2. Law of AccelerationLaw of Acceleration

3.3. Law of Action / ReactionLaw of Action / Reaction

11stst LAW LAW

““An object will An object will remain in remain in its current state of its current state of motionmotion (stationary or (stationary or moving) moving) unlessunless acted acted upon by a force.upon by a force.””

22ndnd LAW LAW

Force = Mass x Force = Mass x Acceleration Acceleration

““The The greater the massgreater the mass of an object, then of an object, then thethe greater force requiredgreater force required to to change its state of change its state of motionmotion (stationary or (stationary or moving)”moving)”

OROR

“ “The acceleration of a The acceleration of a body is body is directly directly proportionalproportional to the to the size of the forcesize of the force applied and in the applied and in the direction of the forcedirection of the force applied.”applied.”

33rdrd LAW LAW

““For every For every actionaction there is an there is an equal and equal and oppositeopposite reactionreaction””