Mechanics of movementMechanics of movement

A2 Sports StudiesA2 Sports StudiesMr JenningsMr Jennings

What you need to know…..What you need to know…..

Mechanics of movementMechanics of movement Vectors and scalars; velocity, Vectors and scalars; velocity,

accelerationacceleration Momentum/impulse in sprintingMomentum/impulse in sprinting Newton’s Laws applied to Newton’s Laws applied to

movementsmovements Application of forces in sporting Application of forces in sporting

activitiesactivities

This is a daunting topicThis is a daunting topic However, the questions always focus However, the questions always focus

on very similar scenarioson very similar scenarios Very quickly you will become familiar Very quickly you will become familiar

with the key terms and concepts with the key terms and concepts

ForcesForcesA force is:A force is:

““A force is that which alters or tends A force is that which alters or tends to alter a body’s state of rest to alter a body’s state of rest or of uniform motion in a straight or of uniform motion in a straight line.”line.”

If a body changes direction or velocity, If a body changes direction or velocity, a force has been applied to ita force has been applied to it

All performance are affected by All performance are affected by forcesforces

How is this athlete affected by How is this athlete affected by forces?forces?

Forces cause us to move, Forces cause us to move, change direction and to stop. change direction and to stop. Gravity keeps her on the floorGravity keeps her on the floor

Key TermsKey Terms

DisplacementDisplacement VelocityVelocity AccelerationAcceleration

Displacement or DistanceDisplacement or Distance

AB

Length of journey in Length of journey in meters =meters =

Straight line from start to finish Straight line from start to finish in meters = in meters =

distancedistance

displacementdisplacement

Displacement and distanceDisplacement and distance

In a 400m race?In a 400m race? In a 400m race on a track the length In a 400m race on a track the length

of the path the athlete follows of the path the athlete follows (distance) is 400m but their (distance) is 400m but their displacement will be zero metres displacement will be zero metres (they finish where they start) (they finish where they start)

Speed or velocitySpeed or velocity

SpeedSpeed is distance / time is distance / time VelocityVelocity is displacement divided by is displacement divided by

timetime Displacement has directionDisplacement has direction Most biomechanics refers to Most biomechanics refers to

displacement and velocitydisplacement and velocity

Speed and velocitySpeed and velocity

Consider a swimmer in a 50m race in Consider a swimmer in a 50m race in a 25m length pool who completes a 25m length pool who completes the race in 60 seconds the race in 60 seconds

Work out her speed and her velocityWork out her speed and her velocity Distance is 50m and displacement is Distance is 50m and displacement is

0m (swimmer is back where they 0m (swimmer is back where they started) so speed is 50/60= 0.83m/s started) so speed is 50/60= 0.83m/s and velocity is 0/60=0 m/s and velocity is 0/60=0 m/s

Physics of sprintingPhysics of sprinting An athlete runs 100m in 15 secondsAn athlete runs 100m in 15 seconds We know their speed is 100/15 = 6.67(ms-1)We know their speed is 100/15 = 6.67(ms-1)

Velocity is a similar concept to speed but includes Velocity is a similar concept to speed but includes the idea of ‘direction’the idea of ‘direction’

All velocities take place in a certain directionAll velocities take place in a certain direction Velocity = displacement/timeVelocity = displacement/time An athlete running 100m in 12s: Velocity = An athlete running 100m in 12s: Velocity =

100/12 = 8.33(ms-1)100/12 = 8.33(ms-1)

Calculating velocityCalculating velocity

Use 100-metre sprinting to calculate Use 100-metre sprinting to calculate athlete’s velocityathlete’s velocity

Plot the velocity curvePlot the velocity curve

What do you notice?What do you notice?

Timing point (displacement in metres)

Distance covered (Metres)

Time to reach this point (seconds)

Start 0 0

10 10 1.720 10 2.930 10 4.040 10 5.050 10 6.060 10 7.170 10 8.380 10 9.690 10 11.0100 10 12.6

What happened?What happened? Velocity varies during raceVelocity varies during race Slow at start (0-40m)Slow at start (0-40m) Fastest in middleFastest in middle Decrease from 60-100mDecrease from 60-100m Why?Why?

• Energy sources- PC system 6 secondsEnergy sources- PC system 6 seconds• Lactate system is slower hence Lactate system is slower hence

deceleration deceleration

Velocity/time graphsVelocity/time graphs

VelocityVelocity

TimeTime

Velocity Velocity changeschanges

AccelerationAcceleration

Average velocity changesAverage velocity changes

Change in velocity over a period of time Change in velocity over a period of time is calledis called

Acceleration =

accelerationacceleration

final velocity – initial velocityfinal velocity – initial velocity

time takentime taken

Velocity

Time

On a velocity-time On a velocity-time graph acceleration is graph acceleration is shown by theshown by the

of the lineof the line

steepness steepness (gradient)(gradient)

Velocity

Time

Highest acceleration?Highest acceleration?

zero acceleration?zero acceleration?

deceleration?deceleration?

Vectors and scalarsVectors and scalars

Displacement, velocity and Displacement, velocity and acceleration have direction as well as acceleration have direction as well as magnitude =magnitude =

Temperature, time, speed, etc do not Temperature, time, speed, etc do not have direction =have direction =

http://www.grc.nasa.gov/WWW/K-12/airplane/vectors.htmlhttp://www.grc.nasa.gov/WWW/K-12/airplane/vectors.html

vectorsvectors

scalarsscalars

Typical questionTypical questionThe Figure shows a velocity/time graph for an elite 100-metre The Figure shows a velocity/time graph for an elite 100-metre

runner.runner.

(i)(i) Use the figure to determine the velocity of the sprinter after 3 seconds, Use the figure to determine the velocity of the sprinter after 3 seconds, andand identify the period of time when the sprinter’s acceleration was the identify the period of time when the sprinter’s acceleration was the greatest.greatest. (2 marks)(2 marks)

(ii)(ii) What is happening to the sprinter between 6 and 11 seconds? Explain What is happening to the sprinter between 6 and 11 seconds? Explain why this occurs.why this occurs. (3 marks)(3 marks)

AnswerAnswer

(i)(i)1. 9.1 1. 9.1 ms-1ms-1 (accept 9.0-9.2); (accept 9.0-9.2);2. 0-1 seconds/s.2. 0-1 seconds/s. 2 marks2 marks(ii)(ii)1. Deceleration/decrease in velocity; (Do not credit 1. Deceleration/decrease in velocity; (Do not credit

slowing down)slowing down)2.2. Lack of ATP;Lack of ATP;3.3. CP breakdown to ATP slowing/limiting;CP breakdown to ATP slowing/limiting;4.4. Due to lack of stored PC;Due to lack of stored PC;5.5. Change to Change to slowerslower lactic acid/alactic/anaerobic lactic acid/alactic/anaerobic

systemsystem max3 marksmax3 marks

From a sport of your choice:From a sport of your choice: Identify 2 examples of when a body’s Identify 2 examples of when a body’s

state of motion gets quickerstate of motion gets quicker Identify 2 examples of when a body’s Identify 2 examples of when a body’s

state of motion gets slowerstate of motion gets slower

What causes these changes in speed What causes these changes in speed and direction?and direction?

There are 2 types of forceThere are 2 types of force• Internal and externalInternal and external

Internal – contraction of musclesInternal – contraction of muscles External – air resistance, gravity and External – air resistance, gravity and

frictionfriction

Forces are Vectors so haveForces are Vectors so have• Magnitude and direction and are represented Magnitude and direction and are represented

by arrowsby arrows

External forcesExternal forces Gravity - Gravity - force pulls objects back down to earthforce pulls objects back down to earth Friction –Friction – objects moving against each other in objects moving against each other in

opposition cause friction. Basketball shoes have opposition cause friction. Basketball shoes have ‘extra grip’ which actually means more friction ‘extra grip’ which actually means more friction whereas ice skates are designed for minimal whereas ice skates are designed for minimal friction friction

Air resistance –Air resistance – friction caused by air moving over friction caused by air moving over a surface. Very different to wind resistancea surface. Very different to wind resistance

Inertia –Inertia – the reluctance to change state of motion. the reluctance to change state of motion. Pushing a car is hard at first but not too hard Pushing a car is hard at first but not too hard once its moving. Once moving though it would be once its moving. Once moving though it would be difficult to stop!difficult to stop!

Newton’s LawsNewton’s Laws

An exam question on these is An exam question on these is extremely straight forward once you extremely straight forward once you have a basic understanding of how have a basic understanding of how they apply to different scenariosthey apply to different scenarios

Newton’s 1Newton’s 1stst Law Law The Law of InertiaThe Law of Inertia

• “ “ a body will remain in it’s state of motion/rest a body will remain in it’s state of motion/rest until affected by a force acting upon it”until affected by a force acting upon it”

A body will be reluctant to change its state A body will be reluctant to change its state of motionof motion

Applying the law:Applying the law: A football being kicked, a sprinter in the A football being kicked, a sprinter in the

start blocks and a snooker ball prior to start blocks and a snooker ball prior to being hitbeing hit

MomentumMomentum Every moving object has Every moving object has massmass andand

velocityvelocity Momentum = mass x velocityMomentum = mass x velocity If two rugby players with same mass If two rugby players with same mass

collide, the one with higher velocity collide, the one with higher velocity winswins

If they have same velocity, the one If they have same velocity, the one with larger mass winswith larger mass wins

Both have larger Both have larger momentummomentum

Newton’s 2Newton’s 2ndnd Law Law

The Law of AccelerationThe Law of Acceleration

““The rate of change of momentum is The rate of change of momentum is directly proportional to the force causing directly proportional to the force causing the change, and the change takes place in the change, and the change takes place in the direction in which the force was the direction in which the force was applied”applied”

In sport, mass remains constant and so In sport, mass remains constant and so momentum equates to accelerationmomentum equates to acceleration

Applying the 2Applying the 2ndnd Law Law

The magnitude and direction of the The magnitude and direction of the force applied by the sprinter in the force applied by the sprinter in the blocks will determine the magnitude blocks will determine the magnitude and direction of the force received and direction of the force received (acceleration)(acceleration)

Acceleration is proportional to force Acceleration is proportional to force applied (F=ma)applied (F=ma)

Newton’s 3Newton’s 3rdrd Law Law

The Law of reactionThe Law of reaction“ “ for every action there is an opposite and for every action there is an opposite and

equal action force”equal action force” In sport this is usually the performer and In sport this is usually the performer and

the groundthe ground

Applying Newton’s 3Applying Newton’s 3rdrd Law Law The performer cannot move the earth but The performer cannot move the earth but

receives significant accelerationreceives significant acceleration This is called This is called Ground Reaction ForceGround Reaction Force

Action force of Action force of muscle muscle contractioncontraction

Equal and opposite Equal and opposite forceforce

Using Newton’s Laws explain how an Using Newton’s Laws explain how an athlete accelerates out of the blocks at athlete accelerates out of the blocks at

the start of a race.the start of a race.1.1. The athlete remains at constant velocity, at rest, in his The athlete remains at constant velocity, at rest, in his

blocks at the start of a race due to Newton’s First Law – blocks at the start of a race due to Newton’s First Law – the Law of Inertia. In order for him to accelerate an the Law of Inertia. In order for him to accelerate an external force must be applied. external force must be applied.

2.2. As the athlete uses his muscles to generate a force into As the athlete uses his muscles to generate a force into the blocks/ground there will be an equal an opposite the blocks/ground there will be an equal an opposite reaction force pushing him forwards, due to Newton’s reaction force pushing him forwards, due to Newton’s Third Law – the Action-Reaction Law.Third Law – the Action-Reaction Law.

3.3. This resultant force is the external force required to This resultant force is the external force required to overcome the inertia (Newton’s 1st Law) and the athlete overcome the inertia (Newton’s 1st Law) and the athlete accelerates from the blocks.accelerates from the blocks.

4.4. The acceleration of the athlete is in direct proportion to The acceleration of the athlete is in direct proportion to the size of the resultant external force due to Newton’s the size of the resultant external force due to Newton’s Second Law – the Law of Acceleration. The acceleration Second Law – the Law of Acceleration. The acceleration can be calculated using the formula F=ma. can be calculated using the formula F=ma.

Forces in runningForces in running

List as many forces as you can think List as many forces as you can think of acting upon the runner in the next of acting upon the runner in the next picturepicture

Label the force arrow to show the Label the force arrow to show the direction of the forcedirection of the force

Forces acting on a sprinterForces acting on a sprinter

Action force of muscular Action force of muscular contractioncontraction

FrictionFriction

GravityGravity

Air Air resistanceresistance

Equal and opposite Ground Equal and opposite Ground Reaction ForceReaction Force

Forces in high jumpingForces in high jumping

List as many forces as you can think List as many forces as you can think of acting upon the jumper in the next of acting upon the jumper in the next picturepicture

Label the force arrow to show the Label the force arrow to show the direction of the forcedirection of the force

Muscle force Muscle force applied to applied to ground on take ground on take offoff

Large vertical Large vertical ground reaction ground reaction forceforce

GravityGravity Friction between Friction between

foot and groundfoot and ground Air resistance to Air resistance to

forward motionforward motion

Forces in kickingForces in kicking

Explain how Newton’s 3 laws will Explain how Newton’s 3 laws will affect the ball when it is kickedaffect the ball when it is kicked

Label the force arrow to show the Label the force arrow to show the direction of the forcedirection of the force

11stst Law – ball is kicked, overcomes Law – ball is kicked, overcomes inertia and acceleratesinertia and accelerates

22ndnd Law – size and direction of Law – size and direction of acceleration depend on size and acceleration depend on size and direction of the applied forcedirection of the applied force

33rdrd when ball is kicked a fore equal to when ball is kicked a fore equal to the force applied to the ball is felt by the force applied to the ball is felt by the footthe foot

Gravity and friction slow ball downGravity and friction slow ball down

Typical questionTypical question

Use Use Newton’s Three Laws of MotionNewton’s Three Laws of Motion to to explain how a tennis player moves explain how a tennis player moves towards the ball in preparation to play towards the ball in preparation to play a stroke.a stroke. (5 marks)(5 marks)

AnswerAnswerFirst Law – reluctance to change state of motion/constant First Law – reluctance to change state of motion/constant motion/ uniform motion/velocity;motion/ uniform motion/velocity;Force required to change state of motion/overcome inertia of Force required to change state of motion/overcome inertia of player;player;Muscle contractions;Muscle contractions; (Sub max 2 marks)(Sub max 2 marks)

Second Law – magnitude/size of force governs change in Second Law – magnitude/size of force governs change in momentum;momentum;Mass remains constant;Mass remains constant;Force governs magnitude of acceleration given to player;Force governs magnitude of acceleration given to player;And direction;And direction; (Sub max 2 marks)(Sub max 2 marks)

Third Law – Third Law – equalequal and and oppositeopposite reaction force; reaction force;Force applied to ground/ moves performer;Force applied to ground/ moves performer;Ground Reaction Force.Ground Reaction Force. (Sub max 2 marks)(Sub max 2 marks)

Max of 5 marksMax of 5 marksDo not credit Force = Mass x AccelerationDo not credit Force = Mass x AccelerationOnly credit responses that relate to the player not the ball.Only credit responses that relate to the player not the ball.