Biomechanics

1. Biomechanics Section 1: Forces and Levers

2. Biomechanics • “Describe how functional anatomy and biomechanical principals relate to performing a physical activity” • Coaching movement • Understanding movement • Optimising movement • Russian Gynastics

3. 1.2 What is a force? A force is defined as a pushor apull

4. 1.3 Centre of Gravity The main force acting on all parts of the body is gravity. We can define the COG as follows: The point in the body at which all parts of the body are in balance OR the point at which gravity is centred. When we stand in the anatomical position, our COG is located around the hip region. Why is COG lower in women than men? More mass is concentrated around the hips and below in women. This gives advantages ion sports requiring balance e.g. beam work in gymnastics.

5. The Axes of Rotation

6. 1.4 Levers A lever consists of three parts • Resistance • Effort • Fulcrum or pivot Levers perform two main functions: • To increase the resistance that can be moved with a given effort, e.g. a crowbar. • To increase the velocity at which an object will move with a given force.

8. Revision

9. Biomechanics Section 2: Motion

10. 3.2 Newton’s Laws of Motion [A] Law 1 An object at rest tends to remain at rest unless acted upon by some external force This is known as inertia Which has more inertia? Why? The 175kg weights have more inertia because it has a greater mass Having a great deal of inertia can be advantageous in some sporting situations. How? If you have a lot of inertia you can be difficult to move e.g. in a rugby scrum, wrestling, judo Of course having a lot of inertia has disadvantages as well in sporting situations. How? If you have a lot of inertia, you require a lot of force or effort to get you moving. It can also mean a decrease in agility.

11. [B] Law 2 If a table tennis ball, tennis ball and bowling ball are each hit or bowled with the same amount of force, which one accelerates the most? Why? The table tennis ball because it is lighter. If the tennis ball is hit with gradually increasing force, what happens to its acceleration? The acceleration will increase with increasing force. In summary, we can say: A. The greater the force, the greater the acceleration B. The smaller the mass, the greater the accelerationwhen a constant force is applied. C. The mass will accelerate in the direction the force is applied. These statements can be summarised by an equation: Force = mass X acceleration F = ma How could you apply Newton’s 2nd Law to sporting situations? The harder you hit the ball, the faster and possibly further it will travel. For example, swinging a golf club slowly with force gives the golf ball less force hence acceleration than if you swung the golf club forcefully.

12. Reaction [C] Law 3 When we apply a force to something it is known as action force The object we apply a force to, applies a force back, a reaction force What other example can you think of? When a ball is bounced, it bounces back in a direction opposite to that in which it was dropped. If these forces are equal, why is earth not pushed backward when we drive out of the starting blocks in a 100 metre race? The earth has a huge mass and therefore huge inertia. We cannot generate enough force to overcome this inertia. Action Reaction Action Reaction Action

13. 3.5 Momentum We can rewrite Newton’s First Law to include momentum: An object that is moving will continue to move in the direction the force was applied until another force is applied. [A] Linear Momentum Momentum can be calculated via an equation: Momentum = mass x velocity (kgms-1) (kg) (ms-1) Use this equation to calculate which athlete has the greatest momentum. Mo (A)= 75 kg x 6.5 ms-1 Mo (B) = 80 kg x 5.5 ms-1 = 487.5 kgms-1 = 440 kgms-1 Player A has the greatest momentum.

14. [B] Angular Momentum Consider the situation of teaching young children how to swing a softball bat. Is it easier for them to swing using a normal grip or a choke grip? Why? The choke grip is easier because the COG of the mass is now closer to the axis of rotation (the hands). Consider an ice skater spinning. How so they speed themselves up in the spin? How do they slow themselves down? To speed up, they bring their body parts closer to the axis of rotation. Then move them out again to slow down. Delete the incorrect option in each case. When the mass is moved closer to the axis of rotation, inertia increases / decreases, and angular velocity increases / decreases. As a consequence the body spins faster. When the mass is moved further away from the axis of rotation, inertia increases / decreases, and angular velocity increases / decreases. As a consequence the body spins slower.

15. Other sporting examples of this principle in action include: 1. Pirouettes in ballet 2. Somersaults in tumbling 3. Springboard diving moves Explain in biochemical terms the relationship that occurs between moment of inertia and angular velocity as the gymnast performs the headstand to forward roll. As the gymnast tucks A – C, the mass is brought closer to the axis of rotation. AS a consequence inertia decreases and angular velocity (speed of roll) increases. As the gymnast opens out from C - E, the mass is moved further from the axis of rotation. Inertia increases, angular velocity decreases. Let us assume that the gymnast is unable to stand at the end of performing the skill, instead they fall backwards. Explain in biomechanical detail what may have happened for this to occur. They opened out too early (inertia increases, angular velocity decreases,) i.e. they don’t have enough speed of rotation to get to the standing position.

16. High • Key: • = INERTIA • = ANGULAR VELOCITY AngularVelocity Inertia Low A C B D E Plot the change in inertia and angular velocity as the gymnast performs a headstand to forward roll

17. 3.6 Conservation of Momentum The Law of Conservation of Momentum states: When objects collide, momentum is conserved throughout. The total momentum before impact (before the ball is hit) is: Equal to the momentum of the bat AND the momentum of the ball Basically: Momentum before impact = momentum after impact

18. Using this concept, explain why: • The white ball in pool slows down after impacting the black. Some of the momentum of the white ball is passed on to the black ball. b. When suddenly braking in a car, your body moves forward (thankfully you are wearing a seatbelt). The momentum of the car is transferred to your body. This is why objects in a car are propelled forward on braking. Remember, the total momentum of the club and ball before impact must equal… The total momentum of the club and ball AFTER impact

19. Club momentum Mo = m x v = 0.35kg x 30m/s = 10.5 kgm/s Ball momentum Mo = m x v = 0.04kg x 0m/s = 0 kgm/s-1 (because the ball is stationary) Total momentum Club + Ball = 10.5 kgm/s + 0kgm/s = 10.5 kgm/s + + Step 1: Calculate the momentum of the club and ball before impact. Step 2: Calculate the momentum of the club and ball after impact. Club momentum Mo = m x v = 0.35kg x 25m/s = 8.75 kgm/s Ball momentum If total Mo must be 10.5 kgm/s and the club is 8.75 kgm/s the ball must be: 10.5 kgm/s – 8.75 kgm/s = 1.75 kgm/s Total momentum = 10.5 kgm/s + +

20. Mo mass velocity Step 3: Since we now know the momentum of the ball after impact, we can calculate the velocity of the ball by rearranging the momentum equation. • An ice hockey player with a mass of 85 kg propels themselves forward with a velocity of 5 m/s. What is their momentum? Mo = m x v = 85 kg x 5 m/s = 425 kgm/s Ball Velocity (m/s) V = Mo ÷ m = 1.75 kgm/s ÷ 0.04 kg = 43.75 m/s

21. Stick momentum (before) Mo = m x v = 2kg x 25m/s = 50 kgm/s Puck momentum (before) Mo = m x v = 0.5kg x 2m/s = 1.0 kgm/s-1 (because the ball is stationary) Total momentum (before) = 51 kgm/s + + b. Calculate the velocity of the puck after impact. Using this information, the velocity of the puck is… Stick momentum (after) Mo = m x v = 2kg x 17m/s = 34 kgm/s Puck momentum (after) 51kgm/s – 34kgm/s = 17kgm/s Total momentum (after) = 51 kgm/s + + V = Mo ÷ m = 17 kgm/s ÷ 0.5 kg = 34 m/s

22. c. Explain using the principle of conservation of momentum, why the hockey puck moves toward the goal faster than the 2m/s it was originally travelling at. Because some of the momentum of the player and stick has been passed to the puck on impact. d. (Extension) Use this information to calculate the hockey player’s velocity after striking the puck. Player Mo before = 425 kgm/s but puck after impact = 17 kgms-1 Change in Moof player = 425 khms-1 = 408 kgms-1 V = Mo ÷ m= 408 kgms-1 ÷ 85 kg = 4.80 m/s

23. 3.7 Generating Momentum [A] Generating Linear Momentum Consider the hockey player. How do they give maximum momentum to the ball when it is flicked? What are they doing? Get down low, step into the shot, strong grip on lever (stick), use whole body in shot, follow through, good range of motion. [1] Using body Segments We should look to se as many body segments as possible when trying to give an object maximum momentum. Why? Because we can maximise the muscular force that each muscle group associated with each segment can generate. In the hockey illustration, what body segments are being used? Legs, hip, trunk, shoulder, arms and wrist.

24. [2] Stretch Out Before we begin the sequence of movements, such as the throwing action, we should stretch muscles out to their optimal length. Why? It allows the muscle to be contracted with optimum force. In the hockey illustration, how do we see this principle being applied? Large step forward. Extension of arms around the stick. [3] Sequencing of Body Segments In effect we use the body like a giant whip. What are the benefits of this? The momentum generated by larger segments is passed onto smaller ones until we male contact/release etc. In the hockey illustration, how do we see this principle being applied? Legs – trunk – arms – wrist – stick - ball

25. [4] Timing of Body Segments What could happen if the timing of body segments is “out of order”? Not only does the movement lack co-ordination but maximum force generated can be lessened. How does correct timing ensure maximum momentum? It means we use those larger muscle groups first and the smaller muscle groups last. [5] Full Range of Motion What are the benefits of this? The greater the range of motion, the higher the speed of the extremities on release/contact. Using your knowledge of generating momentum, explain how the athlete generates maximum momentum to the javelin upon release. 1. They use the large muscle groups of the leg and trunk to generate force initially. This is then passed to the shoulder, arm and finally hand upon release of the javelin. 2. They fully extend the arm (at shoulder) prior to the throwing action. 3. The timing is legs – trunk – shoulder – arm – hand – javelin 4. The arm moves through its full range of motion to maximise lever length and force summation.

26. [B] Generating Angular Momentum An eccentric force is… A force applied to one side of the COG Draw in the position of the force that needs to be applied in order to generate topspin and backspin on the balls below. TOP SPIN FORCE FORCE BACK SPIN

27. Draw in the body position of the athlete in order to initiate a dive roll in gymnastics. Explain this position. The COG is in front of the feet (where the force will be applied). This causes a turning force. How can an athlete generate more angular momentum to the body, or object? Apply greater initial force or move the COF further away from the point of force application. COG force

28. 4.2 Factors Affecting Projectile Motion What is the effect on the projectile of the vertical component? To give it height What is the effect on the projectile of the horizontal component? To give it distance The factors affecting the flight path of a projectile are: 1. Gravity 2. Air resistance 3. Speed of release 4. Angle of release 5. Height of release 6. Spin

29. [A] Gravity What is the effect of gravity on a projectile? It decreases the height the projectile can attain [B] Air Resistance Draw the typical flight path of a badminton shuttle. There are several key factors that bring air resistance into play: 1. The larger the surface to volume ratio, the more air resistance will affect the object, e.g. a badminton shuttle compared to a golf ball. 2. The surface of the object. If the surface is rough then air resistance will be greater. 3. Speed. As speed increases, so does air resistance, e.g. a space shuttle (friction). 4. Mass. The smaller the mass (lighter the object), the more air resistance will affect it. How can we make sure we still get good distance from our projectile? Have a lower angle of release. Rugby players will kick the ball low.

30. Initial Vertical velocity Direction of flight [C] Speed of Release Generally the greater the speed of release, the greater the distance gained What are the advantages of having a high initial vertical velocity? It will result in a longer flight caused by more height. What are the advantages of having a high initial horizontal velocity? It will result in a longer flight time and good distance. In which sports would a high initial vertical velocity be of advantage? Gymnastics tumbling, high jump, ski jump (tricks). In which sports would a high initial horizontal velocity be of advantage? Long jump, ski jump (distance), vaults in gymnastics. Initial Horizontal velocity

31. [D] Angle of Release In sporting situations the angle of release is usually always lower, around 35˚ to 45˚. Why? Air resistance of the body. The take-off point is usually higher than the landing point, e.g. long jump What would happen if the angle of release were too high for a given activity? Poor distance gained. What would happen if the angle of resistance were too low for a given activity? Poor flight time and possibly poor distance. 1. Sports in which distance is important have a lowerangle of release 2. Sports in which height or flight time is important have a higherangle of release

32. [E] Height of Release Why might this be? Time in the air will be greater. Would this mean that a golfer hitting a ball off the top of a hill would hit it further than a golfer at the bottom of the hill? Why? YES – the ball will stay in the air longer so will have a greater chance to fly further. This assumes the same club and force is used. In what other sports is application of this principle important? Javelin. Hold the javelin up high to gain a greater height of release. The reason behind this can be summarised as follows: 1. As the height of release increases, the angle of release decreases. 2. As the height of release decreases, the angle of release increases.

33. [F] Spin What happens to the distance achieved with a topspin shot compared to one with backspin? A topspin shot gives poorer distance compared to backspin. • Range is decreasedwith topspin • Range is increasedwith backspin What will happen with a backspin shot? A region of high pressure (H) is created under the ball and low pressure (L) above the ball. Air moves from H-L. As a consequence the ball tends to ‘stay up’ longer. Draw this on the two balls below: TOPSPIN BACKSPIN H L DIRECTION OF BALL DIRECTION OF BALL L H

34. 6.2 Phases of Execution Most complex skills can be broken down into three phases of execution: 1. Preparation phase 2. Execution phase 3. Post action/follow through phrase Label each diagram accordingly. (From left to right) 1,2,3 How would you describe the key features of each phase? What is its purpose? Phase 1: This is where the athlete sets themselves up to execute the skill. Mental preparation. Addressing the hockey ball (as in example above) Phase 2: This is the force producing movements required to perform skill. In this phase the principles of force summation, timing etc are used. Phase 3: This allows forces to be controlled or dissipate to prevent loss of control or injury.

35. Key biomechanical principle To be considered Preparation Phase Execution Phase Follow-through Newton’s Laws of Motion Inertia (1st Law) Body is positioned ready to overcome the inertia of the ball and change its direction. Body is being prepared to move. Greater forces will be required to overcome the inertia of the body compared to the ball because the player weighs more. The muscles have to work hard now to decrease the forces generated during preparation and execution to maintain control. The greater the forces that were generated, the greater the forces required to slow down and control the movement in the follow through. Acceleration & Force (2nd Law) The greater the force that can be applied to the ball, the greater the acceleration of the ball. By using correct force summation (timing, sequencing, body segments, stretch and range of motion), large forces can be generated that will be passed on to the ball.

36. Key biomechanical principle To be considered Preparation Phase Execution Phase Follow-through Newton’s Laws of Motion Generating Momentum (Force Summation) For every action there is an equal and opposite reaction. If a lot of force is given to the ball it will react and travel a good distance. The ball will travel in the direction that the force is applied. The ball will travel in the direction that the force is applied, Therefore, if the stick follow through is toward s they target, that is the direction the ball will travel in. Action & Reaction (3rd Law) Body segments Stretching out Sequencing of segments Timing Range of motion The sequence and timing of body segments is legs then hips then trunk then shoulders then arms and finally hands. The stick head will move quickly through the range of motion generating large forces on contact with ball. The extension of the arms and stepping forward means muscles will be at optimum force. This also allows for the greatest possible range of motion allowing for greater force to be generated. The player may be going through the movements in their head to make sure the correct body part adds the movement at the correct time. Body is positioned to increase the chances of this happening.

37. Key biomechanical principle To be considered Preparation Phase Execution Phase Follow-through Transfer & Conservation of momentum Stability & Balance The player positions the body such that momentum can be transferred through the body to the ball. By ensuring correct sequencing and timing of body segments, they will enhance the transfer of momentum As they move through the execution phase, momentum generated by the legs and hips moves to the trunk, then shoulder, arms and finally to the stick. Following contact, some of the momentum is transferred to the ball and it begins its flight path. Momentum is conserved throughout the movement (ball and body) The follow through is designed to reduce the momentum in the system so the player remains stable and ready to move on to the next skill. Centre of gravity Base of support Line of gravity motion The rear leg stays back as the stick travels in front of the body because, as one part of a body moves away from the centre of gravity, another body part must move in the opposite direction to ensure balance is maintained. The stable body position ensures the body is balanced and controlled before executing the shot. The centre of gravity (COG) lies within the margins of the base of support (BOS) The large step towards the target increases the size of the abase of support meaning that as the player executes the shot, their centre of gravity remains within the base of support, keeping them stable and balanced throughout.

38. Key biomechanical principle To be considered Preparation Phase Execution Phase Follow-through Projectile Motion The player positions the stick on the bottom half of the ball in order to get ‘under’ it. The angle at which the stick contacts the ball will help determine the angle of release and therefore how high and how far it will go. With force summation, the ball will be given a certain amount of speed upon release. The greater the force given to it, the greater the speed of release. If the player drops the right shoulder and lowers their body behind the ball, it will be given more height rather than distance at take-off (increased angle) Speed of release Height of release Angle of release Spin The follow through will help determine the final path. Of the player ‘hooks; the stick, the shot too will be hooked.