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Mechanics of movement A2 Sports Studies Mr Jennings
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What you need to know….. <ul><li>Mechanics of movement </li></ul><ul><li>Vectors and scalars; velocity, acceleration </li></ul><ul><li>Momentum/impulse in sprinting </li></ul><ul><li>Newton’s Laws applied to movements </li></ul><ul><li>Application of forces in sporting activities </li></ul>
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<ul><li>This is a daunting topic </li></ul><ul><li>However, the questions always focus on very similar scenarios </li></ul><ul><li>Very quickly you will become familiar with the key terms and concepts </li></ul>
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Forces <ul><li>A force is: </li></ul><ul><li>“ A force is that which alters or tends to alter a body’s state of rest or of uniform motion in a straight line.” </li></ul><ul><li>If a body changes direction or velocity, a force has been applied to it </li></ul>
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<ul><li>All performance are affected by forces </li></ul><ul><li>How is this athlete affected by forces? </li></ul><ul><li>Forces cause us to move, change direction and to stop. Gravity keeps her on the floor </li></ul>
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Displacement or Distance A B Length of journey in meters = Straight line from start to finish in meters = distance displacement
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Displacement and distance <ul><li>In a 400m race? </li></ul><ul><li>In a 400m race on a track the length of the path the athlete follows (distance) is 400m but their displacement will be zero metres (they finish where they start) </li></ul>
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Speed or velocity <ul><li>Speed is distance / time </li></ul><ul><li>Velocity is displacement divided by time </li></ul><ul><li>Displacement has direction </li></ul><ul><li>Most biomechanics refers to displacement and velocity </li></ul>
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Speed and velocity <ul><li>Consider a swimmer in a 50m race in a 25m length pool who completes the race in 60 seconds </li></ul><ul><li>Work out her speed and her velocity </li></ul><ul><li>Distance is 50m and displacement is 0m (swimmer is back where they started) so speed is 50/60= 0.83m/s and velocity is 0/60=0 m/s </li></ul>
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Physics of sprinting <ul><li>An athlete runs 100m in 15 seconds </li></ul><ul><li>We know their speed is 100/15 = 6.67(ms-1) </li></ul><ul><li>Velocity is a similar concept to speed but includes the idea of ‘direction’ </li></ul><ul><li>All velocities take place in a certain direction </li></ul><ul><li>Velocity = displacement/time </li></ul><ul><li>An athlete running 100m in 12s: Velocity = 100/12 = 8.33(ms-1) </li></ul>
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Calculating velocity <ul><li>Use 100-metre sprinting to calculate athlete’s velocity </li></ul><ul><li>Plot the velocity curve </li></ul><ul><li>What do you notice? </li></ul>
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12.6 10 100 11.0 10 90 9.6 10 80 8.3 10 70 7.1 10 60 6.0 10 50 5.0 10 40 4.0 10 30 2.9 10 20 1.7 10 10 0 0 Start Time to reach this point (seconds) Distance covered (Metres) Timing point (displacement in metres)
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What happened? <ul><li>Velocity varies during race </li></ul><ul><li>Slow at start (0-40m) </li></ul><ul><li>Fastest in middle </li></ul><ul><li>Decrease from 60-100m </li></ul><ul><li>Why? </li></ul><ul><ul><li>Energy sources- PC system 6 seconds </li></ul></ul><ul><ul><li>Lactate system is slower hence deceleration </li></ul></ul>
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Velocity/time graphs Velocity Time Velocity changes
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Acceleration <ul><li>Average velocity changes </li></ul><ul><li>Change in velocity over a period of time is called </li></ul>acceleration final velocity – initial velocity time taken Acceleration =
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Velocity Time On a velocity-time graph acceleration is shown by the of the line steepness (gradient)
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Velocity Time Highest acceleration? zero acceleration? deceleration?
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Vectors and scalars <ul><li>Displacement, velocity and acceleration have direction as well as magnitude = </li></ul><ul><li>Temperature, time, speed, etc do not have direction = </li></ul><ul><li>http://www.grc.nasa.gov/WWW/K-12/airplane/vectors.html </li></ul>vectors scalars
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Typical question <ul><li>The Figure shows a velocity/time graph for an elite 100-metre runner. </li></ul>(i) Use the figure to determine the velocity of the sprinter after 3 seconds, and identify the period of time when the sprinter’s acceleration was the greatest. (2 marks) (ii) What is happening to the sprinter between 6 and 11 seconds? Explain why this occurs. (3 marks)
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Answer <ul><li>(i) </li></ul><ul><li>1. 9.1 ms-1 (accept 9.0-9.2); </li></ul><ul><li>2. 0-1 seconds/s. 2 marks </li></ul><ul><li>(ii) </li></ul><ul><li>1. Deceleration/decrease in velocity; (Do not credit slowing down) </li></ul><ul><li>2. Lack of ATP; </li></ul><ul><li>3. CP breakdown to ATP slowing/limiting; </li></ul><ul><li>4. Due to lack of stored PC; </li></ul><ul><li>5. Change to slower lactic acid/alactic/anaerobic system max3 marks </li></ul>
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<ul><li>From a sport of your choice: </li></ul><ul><li>Identify 2 examples of when a body’s state of motion gets quicker </li></ul><ul><li>Identify 2 examples of when a body’s state of motion gets slower </li></ul><ul><li>What causes these changes in speed and direction? </li></ul>
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<ul><li>There are 2 types of force </li></ul><ul><ul><li>Internal and external </li></ul></ul><ul><li>Internal – contraction of muscles </li></ul><ul><li>External – air resistance, gravity and friction </li></ul><ul><li>Forces are Vectors so have </li></ul><ul><ul><li>Magnitude and direction and are represented by arrows </li></ul></ul>
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External forces <ul><li>Gravity - force pulls objects back down to earth </li></ul><ul><li>Friction – objects moving against each other in opposition cause friction. Basketball shoes have ‘extra grip’ which actually means more friction whereas ice skates are designed for minimal friction </li></ul><ul><li>Air resistance – friction caused by air moving over a surface. Very different to wind resistance </li></ul><ul><li>Inertia – the reluctance to change state of motion. Pushing a car is hard at first but not too hard once its moving. Once moving though it would be difficult to stop! </li></ul>
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Newton’s Laws <ul><li>An exam question on these is extremely straight forward once you have a basic understanding of how they apply to different scenarios </li></ul>
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Newton’s 1 st Law <ul><li>The Law of Inertia </li></ul><ul><ul><li>“ a body will remain in it’s state of motion/rest until affected by a force acting upon it” </li></ul></ul><ul><li>A body will be reluctant to change its state of motion </li></ul><ul><li>Applying the law: </li></ul><ul><li>A football being kicked, a sprinter in the start blocks and a snooker ball prior to being hit </li></ul>
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Momentum <ul><li>Every moving object has mass and velocity </li></ul><ul><li>Momentum = mass x velocity </li></ul><ul><li>If two rugby players with same mass collide, the one with higher velocity wins </li></ul><ul><li>If they have same velocity, the one with larger mass wins </li></ul><ul><li>Both have larger momentum </li></ul>
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Newton’s 2 nd Law <ul><li>The Law of Acceleration </li></ul><ul><li>“ The rate of change of momentum is directly proportional to the force causing the change, and the change takes place in the direction in which the force was applied” </li></ul><ul><li>In sport, mass remains constant and so momentum equates to acceleration </li></ul>
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Applying the 2 nd Law <ul><li>The magnitude and direction of the force applied by the sprinter in the blocks will determine the magnitude and direction of the force received (acceleration) </li></ul><ul><li>Acceleration is proportional to force applied (F=ma) </li></ul>
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Newton’s 3 rd Law <ul><li>The Law of reaction </li></ul><ul><ul><li>“ for every action there is an opposite and equal action force” </li></ul></ul><ul><li>In sport this is usually the performer and the ground </li></ul>
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Applying Newton’s 3 rd Law <ul><li>The performer cannot move the earth but receives significant acceleration </li></ul><ul><li>This is called Ground Reaction Force </li></ul>Action force of muscle contraction Equal and opposite force
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Using Newton’s Laws explain how an athlete accelerates out of the blocks at the start of a race. <ul><li>The athlete remains at constant velocity, at rest, in his blocks at the start of a race due to Newton’s First Law – the Law of Inertia. In order for him to accelerate an external force must be applied. </li></ul><ul><li>As the athlete uses his muscles to generate a force into the blocks/ground there will be an equal an opposite reaction force pushing him forwards, due to Newton’s Third Law – the Action-Reaction Law. </li></ul><ul><li>This resultant force is the external force required to overcome the inertia (Newton’s 1st Law) and the athlete accelerates from the blocks. </li></ul><ul><li>The acceleration of the athlete is in direct proportion to the size of the resultant external force due to Newton’s Second Law – the Law of Acceleration. The acceleration can be calculated using the formula F=ma. </li></ul>
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Forces in running <ul><li>List as many forces as you can think of acting upon the runner in the next picture </li></ul><ul><li>Label the force arrow to show the direction of the force </li></ul>
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Forces acting on a sprinter Action force of muscular contraction Friction Gravity Air resistance Equal and opposite Ground Reaction Force
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Forces in high jumping <ul><li>List as many forces as you can think of acting upon the jumper in the next picture </li></ul><ul><li>Label the force arrow to show the direction of the force </li></ul>
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<ul><li>Muscle force applied to ground on take off </li></ul><ul><li>Large vertical ground reaction force </li></ul><ul><li>Gravity </li></ul><ul><li>Friction between foot and ground </li></ul><ul><li>Air resistance to forward motion </li></ul>
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Forces in kicking <ul><li>Explain how Newton’s 3 laws will affect the ball when it is kicked </li></ul><ul><li>Label the force arrow to show the direction of the force </li></ul>
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<ul><li>1 st Law – ball is kicked, overcomes inertia and accelerates </li></ul><ul><li>2 nd Law – size and direction of acceleration depend on size and direction of the applied force </li></ul><ul><li>3 rd when ball is kicked a fore equal to the force applied to the ball is felt by the foot </li></ul><ul><li>Gravity and friction slow ball down </li></ul>
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Typical question <ul><li>Use Newton’s Three Laws of Motion to explain how a tennis player moves towards the ball in preparation to play a stroke. (5 marks) </li></ul>
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Answer <ul><li>First Law – reluctance to change state of motion/constant motion/ uniform motion/velocity; </li></ul><ul><li>Force required to change state of motion/overcome inertia of player; </li></ul><ul><li>Muscle contractions; (Sub max 2 marks) </li></ul><ul><li>Second Law – magnitude/size of force governs change in momentum; </li></ul><ul><li>Mass remains constant; </li></ul><ul><li>Force governs magnitude of acceleration given to player; </li></ul><ul><li>And direction; (Sub max 2 marks) </li></ul><ul><li>Third Law – equal and opposite reaction force; </li></ul><ul><li>Force applied to ground/ moves performer; </li></ul><ul><li>Ground Reaction Force. (Sub max 2 marks) </li></ul><ul><li>Max of 5 marks </li></ul><ul><li>Do not credit Force = Mass x Acceleration </li></ul><ul><li>Only credit responses that relate to the player not the ball. </li></ul>
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