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IB Sports, Exercise and Health Science Define Force: Topic 4: Biomechanics Forces ____________a push or pull between two objects or bodies. It may involve contact (such as friction) or it may act at a distance (such as gravity). A force changes or tries to change the motion of an object or body. e.g. you can push on a door with force. (vector quantity) Forces are an integral aspect of any study of biomechanics. You can not actually see a force but you can see and experience its effects (Carr 2004). A force can be described as a push or a pull that changes or tends to change the shape or state of motion of an athlete or an object. Think through an example where a force being applied may not change anything about an object or its motion: Answer: Draw a pin-man drawing of a sportsperson standing still, showing (with arrows) all the forces acting on him/her. Sketch a second diagram showing all the forces acting on a runner accelerating and then later on in a race. First one is done for you! Figure 1.2 Forces acting on a runner accelerating Figure 1.1 Forces acting on a sportsperson standing still. Figure 1.4 Forces acting on a high jumper just before takeoff. Figure 1.3 Forces acting on an athlete later in a race. IB Sports, Exercise and Health Science Topic 4: Biomechanics How the body applies and absorbs Force The push or pull which causes motion Measured in newtons (2nd law of motion) Biomechanics can be defined as the science that examines internal and external forces acting on the human body and the effects produced by these forces Internal Force - produced by muscles ● A sprinter running down the track is generating internal forces in the leg muscles during each stride. ● The net result of these internal forces is a sequence of pushes against the ground with the foot External Force: ● With each push against the track (note that the track or ground is an external force), the ground pushes back against the athlete and so the athlete moves forward. ● Other external/outside forces also act against the athlete such as gravity (vertical direction downwards towards the centre of the earth) and air resistance (horizontal motion) Force can: ● Cause a body at rest to move ● Cause a moving body to slow down, stop, increase its speed or change its direction ● Causes objects to change shape or move (accelerate), has a direction and is therefore a vector Examples ● ● ● ● ● ● Throwing a ball (move) Catch a ball (stop an object) Hitting a shuttle cock (change direction) Speed up when running (change speed) Wrestling (balance a force keeping it still) Dribbling a soccer ball (balance another force to keep object moving) IB Sports, Exercise and Health Science Topic 4: Biomechanics 1. Think of the vertical forces acting on a high jumper just before take-off. 2. With your thoughts and your understanding of Newton’s Laws of Motion (research if you don’t know already) to explain why the high jumper is able to take off. Watch this video link to help you Answer: Forces have both a magnitude and direction which combine to form a force vector. They are measured in Newtons (N). 5. If the vertical upward ground reaction force on the jumper is 1400 N, and the weight of the jumper is 600N, estimate the net upward force acting on him/her. Answer: Net upward force F = 1400 - 600 = _______________ Some different types of force in our world are _________force, impulse force, gravitational force and __________ force. Forces can cause different types of motion (movement) in an object: (please describe and give examples other than the Tennis Investigation you have completed). Linear - Curvilinear - Angular (Rotation)- General- Remember that gravity acts downwards (towards the centre of the Earth) on all objects on the surface of the Earth, and the force due to gravity is called the _____________ IB Sports, Exercise and Health Science 4.3.2 Topic 4: Biomechanics Analyze velocity-time, distance-time graphs of sporting activities. Motion Graphs Answer the following questions individually IB Sports, Exercise and Health Science Topic 4: Biomechanics 4.3.1 Define the terms displacement, velocity, acceleration, speed, force. Scalars and Vectors A scalar quantity is ________________________________ A vector quantity is _______________________________ Define the terms force, speed, velocity, displacement, acceleration, momentum and impulse as ‘Scalar’ or ‘Vector’ in the table below. (Go to See http://www.physicsclassroom.com/class/1dkin/u1l1b.cfm) Scalar Vector Quantities Distance and Displacement Define: Distance: ______________________________ Displacement: _______________________________ IB Sports, Exercise and Health Science Topic 4: Biomechanics Speed and Velocity Define: Speed: __________________________________ Velocity: __________________________________ Momentum: _______________________________________ Calculate the following: (show all working) 1. Lionel Messi kicks a ball 6.5 meters. How much time is needed for the ball to travel this distance if its velocity is 22 meters per second, south? 2. Andy Murray serves a tennis ball to Rafael Nadal. It travels 9.5 meters south in 2.1 seconds. a. What is the velocity of the tennis ball? (b) If the tennis ball travels at constant speed, what is its velocity when Nadal returns Murray’s serve? ACCELERATION Define acceleration: _______________________________________ Calculate the following: (show all working) 1. Michelle Kwan prepares for a jump by increasing her velocity from 2.0 m/s to 10.0 m/s in 3.0 seconds. What is her acceleration? 2. As he climbs a hill, cyclist Bradley Wiggins slows down from 25 km/hr to 6 km/hr in 10 seconds. What is his deceleration? IB Sports, Exercise and Health Science Topic 4: Biomechanics CASE STUDY: Hero or villain? Ben Johnson and the dirtiest race in History (James Montague, Mon July 23, 2012) http://www.cnn.com/2012/07/23/sport/olympics-2012-ben-johnson-seoul-1988-dirtiestrace/index.html Ben Johnson was the last man to settle into his blocks at the Seoul Olympic Stadium. It was September 24, 1988, a heartbeat before the start of the 100 meters final and what was to become the most infamous sporting moment in Olympic history. Johnson, like the rest of an-all star field that included then Olympic champion and fierce rival Carl Lewis, former world record holder Calvin Smith and future gold medalist Linford Christie, paced back and forth like caged panthers seeking the psychological advantage of settling last. The field stretched, hopped and feinted as they pretended not to look at each other. Johnson merely stared straight ahead, unblinking. Inevitably it was he who won the first battle. The gun fired and the Canadian leaped -- literally leaped -- from his starting position into a lead he would never lose. Just 9.79 seconds later he had smashed the world record in a display of power and awe never before seen in track and field, against the greatest field of sprinters ever collected. "Nobody," Johnson recalls in an interview with CNN, laughing in deep, long chugs, "nobody could touch my start." What happened next has been seared into the collective memory of the Olympics ever since. The image of a medal ceremony, more than 24 hours later where Carl Lewis still can't come to terms with where Johnson had found his extra power; the incredulity on the faces of the journalists present; the press conference afterward where a triumphant Johnson eulogized. "I'd like to say my name is Benjamin Sinclair Johnson Jr, and this world record will last 50 years, maybe 100," he had told the room. Later he said: "A gold medal -- that's something no one can take away from you." But they could take it away from him. And they did. Just 24 hours later Johnson had failed a drugs test when traces of the banned steroid stanozolol were found in his urine. And after the IOC delegation arrived at his room. Johnson handed the medal back to the IOC, much to the consternation of his mother. […] The dirtiest race in history The scene was set for the greatest 100m final of all time at Seoul. In many respects it still is, despite the taint of drugs. Only two of the eight runners remained clean throughout their careers: American sprinter Calvin Smith and the Brazilian Robson da Silva. But the race, even today, has an explosive power that makes it impossible to ignore, with four of the field breaking the 10 second barrier. Johnson, perhaps unsurprisingly, believes it is still the greatest race of all time. "Regardless what the IOC think, it's definitely the best race ever run even though I hadn't run my best race yet and you can tell that I have more fuel left in the tank," he explains before claiming that drugs don't actually make you run faster. IB Sports, Exercise and Health Science Topic 4: Biomechanics "You only cheat if no one else was not doing it. I was aware of what other people were doing in the field. I just did it better than anyone else. It doesn't make you a fast runner ... It was my training regime that was better than the rest of the world. My training was tailored for Ben Johnson and my coach was a genius. Now the whole world is using my program." Johnson will always be a pariah, synonymous with those blistering few seconds when he flew too close to the sun before crashing back to earth. Yet the experience hasn't diminished his belief that he still deserves a place among the pantheon of greats. "The runners today can't compare to what I was running 25 years ago," he claims, citing better, harder tracks more suited to the modern generation of sprinters. He believes he would break the 9.5 second barrier if running today. "No sprinter today could bench-press 395 pounds. In 1987 to '88, I won 25 finals against the best sprinters and that never happened today. Unbeatable." IB Sports, Exercise and Health Science 4.3.11 Topic 4: Biomechanics Explain the factors that affect projectile motion at take-off or release. Projectile Motion: Use the vocabulary below to fill in the blanks throughout this exercise. You may use each of the words or phrases as many or as few times as you need. Horizontal Height Parabolic Less Length Decreases air pressure Higher Length Projectile Distance Air resistance topspin poorer initial vertical velocity speed of release height of release initial horizontal velocity angle of release surface to volume ratio rough gravity trajectory vertical increases backspin 1. A ______________ is considered to be any object or body released into the air. 2. All projectiles have a _____________ flight path. The flight path of a projectile is known as the _____________ 3. The ________________ of a projectile consists of a _______________and _________________ component. 4. The _________________ component gives the projectile _________________ . 5. The _________________ component gives the projectile __________________ For example, if you throw a ball straight up into the air the trajectory has only a ___________ component. 6. When you throw a ball to a friend that is standing 20 metres away from you the trajectory has a ____________________component as well. (Label the diagram below). IB Sports, Exercise and Health Science Topic 4: Biomechanics Gravity 7. ______________ will affect a projectile as it will decrease the height the projectile can obtain. 8. The force of ______________ acts on the object to pull it back to earth, limiting the _______________ component of the projectile. Air Resistance 1. As a projectile moves through the air it is slowed down by __________________ 2. ___________________ will decrease the __________________ component of the trajectory. 3. The effect of __________________ is relatively small but needs to be considered. 4. A badminton shuttle has greater ___________ than a golf ball as the holes in it gives it a _________________________ 5. Objects with a ______________ surface will also have increased ___________________. 6. _________________: The speed of a projectile also affects _________________ as friction increases with velocity. 7. The smaller the __________________ of an object, the more air resistance will affect it. 8. This is evident when considering the difference between throwing a feather and a stone. Extension: Because air resistance affects the horizontal component of a projectiles trajectory, the effect of it can be minimized by lowering the _______________________ IB Sports, Exercise and Health Science Topic 4: Biomechanics Speed of Release Speed or velocity is directly related to distance. The greater the _________________ the greater the distance covered in flight. It is divided into two components: a) b) ________________________ ________________________ Having a higher ___________________ will increase the _____________________ of the trajectory, resulting in a longer flight path. This would be an advantage in sports which require good height, such as tumbles in gymnastics, high jump and ski jumping (tricks). Extension: give another example here ______________________ Having a higher _____________________ will increase the _____________________ of the flight time and therefore the distance covered. This would be an advantage in sports, which primarily require good distance, such as long jump, ski jumping (distance), and vaults in gymnastics. Extension: give another example here: ____________________ IB Sports, Exercise and Health Science Topic 4: Biomechanics Angle of Release The ______________changes the relationship between the horizontal and vertical components of a projectile. The ideal ____________is 45 degrees, assuming there is no ______________and the take off and landing points are the same height. If the ____________is greater or less than 45 degrees, the distance covered in flight will be ____________ Extension: In sporting situations the angle of release is often lower, around 35 degrees to 45 degrees. This is because the __________________of the body and because the takeoff point is usually higher than the landing point, e.g., long jump. IB Sports, Exercise and Health Science Topic 4: Biomechanics Height of Release 1. The higher the _____________the greater the _______________covered in flight. This is because the higher the projectile is released; the longer it will be in the air. 2. The _______________of the trajectory will be acting on the projectile for longer. 3. An example of this is throwing a javelin. In javelin, to gain more ____________athletes will hold the javelin up ____________ to create a greater ________________. There is a relationship between height of release and angle of release. As the height of release ______________ the angle of release _______________ As the height of release_________________, the angle of release ________________ For example, when shooting, basketball players will have a lot lower angle of release than shorter basketball players to shoot the ball at the same hoop height. Spin The amount and direction of _________________acting on a projectile will directly affect the _____________a projectile will travel. The reason for this is the _____________acting on the ball. IB Sports, Exercise and Health Science Topic 4: Biomechanics Extension example: 1. In a tennis shot, ____________gives poorer distance compared to___________. 2. A topsin shot creates a region of high pressure on top of the ball and a region of low pressure below. 3. Air moves from a region of __________ to ____________pressure and as a consequence the ball will dip suddenly, decreasing the vertical component of the trajectory. The opposite is true for a backspin. PROJECTILE MOTION PAST PAPER QUESTION 1.Discuss how the factors that affect projectile motion can influence shot put technique. (6) IB Sports, Exercise and Health Science 4.3.7 Topic 4: Biomechanics Define Newton’s three laws of motion Newton’s First Law “An object will remain at rest or continue with constant velocity unless acted on by an unbalanced force”. This means that bodies or objects stay where they are or keep moving unless acted on by an unbalanced force. This is sometimes known as the law of inertia. Outline the forces involved when objects that are thrown or hit on earth and why they do not continue in their state of motion. Is there an environment where this state of motion can be maintained forever? Forces acting on thrown objects Answer: The effects that a force has on an object is affected by the mass of the object. If it is a light object it will be more easily affected as compared to a heavier object. This relates to an objects resistance to motion. Otherwise known as ______________ E.g. which person has the most inertia or resistance to moving and state why you have chosen that person? a. David Beckham – Football player(78kg) b. Richie McCaw – Rugby player(106kg) Answer: IB Sports, Exercise and Health Science Topic 4: Biomechanics Having a lot of inertia or mass can be an advantage in sport but it can also be a disadvantage. Think through an advantages and disadvantages of a small or large inertia and discuss below: Small Inertia Advantage Disadvantage Rugby player Climber A golf club Large Inertia Advantage Disadvantage Rugby player Climber A golf club A common misconception about rock climbing is that it’s all about strength. What is more important is proper technique, which requires excellent balance and flexibility. Also, the secret behind rock climbing strength is not absolute power, but power relative to your own body weight. Rock climbing is one area where size doesn’t matter. What matters is your ability to pull your own weight. One consequence of the requirements of rock climbing is that women are often more likely to have what it takes than men, particularly when it comes to balance and flexibility. Newton’s Second Law What is Newton’s 2nd Law Answer: IB Sports, Exercise and Health Science Topic 4: Biomechanics INDIVIDUAL ACTIVITY Complete the sentences uses the terms ‘faster’ and ‘ slower’ . 1. The greater the force that is applied, the acceleration. the 2. The lesser the force that is applied, the acceleration. the 3. If the same force is applied to an object with a large mass, it will have a acceleration. 4. If the same force is applied to an object with a small mass, it will have a acceleration. Complete the following calculations Bradley Wiggin’s bicycle has a mass of 9.1 kilograms. He accelerates at a rate of 1.79 m/s2. Calculate the net force that is accelerating the bicycle. F = MA Mo Farah has a mass of 65 kilograms. He produces a force of 84 Newtons between the ground and his running shoes. How fast does he accelerate? F = MA A = F/M IB Sports, Exercise and Health Science 4.3.2 Topic 4: Biomechanics Analyze force-time graphs of sporting activities. Part A: Momentum Define Momentum: Answer: Individual Activity Calculate momentum for the following problems Scott Macartney, a US Olympic Ski Team member was going 39 m/s in the downhill ski race when lost his balance and fell. He has a mass of 65Kg. What was his momentum? If you can run 6.7 m/s while holding a 3.5 Kg shot put, how much momentum does the shot put have? IMPULSE • Answer the following questions as you watch the video (http://www.youtube.com/watch?v=qOkvOnLgwrY) How can you change an object’s momentum? 1. Define impulse 2. Which factor transforms a force into an impulse? 3. What is the relationship between impulse and change in momentum? 4. Why should you follow through when hitting a ball? IB Sports, Exercise and Health Science Topic 4: Biomechanics Describe the relationship between linear momentum and linear impulse in the context of Newton’s Second Law Calculate impulse for the following problems 1. A football player kicks a ball with a force of 50N. Find the impulse on the ball if his foot stays in contact with the football for 0.01s. 2. A hockey player applies an average force of 80N to a 0.25kg hockey puck for a time of 0.2s. Determine the impulse experienced by the hockey puck. INDIVIDUAL ACTIVITY We have seen above that muscular forces can have many effects on objects. Whenever a force is being applied it always takes time. When a person applies a force over a certain time then we can say that they have applied an impulse. How force and time are combined depends on: the physical capabilities of the person applying the force eg. compare elite athletes to beginners in a task the requirements of the task: compare sprinting verses rowing, speeding something up verses slowing something down ... Why are the following variables important in maximising impulse? 1.Muscular strength and speed (power): Answer: 2.Flexibility: Answer: IB Sports, Exercise and Health Science Topic 4: Biomechanics Knowing that the area under the curve equals the impulse that a person has applied look at the graphs illustrated below and then explain why following through with a bat swing increases the velocity and potential distance that a ball will travel. Question Explain why ‘follow through’ with a bat swing increases the velocity and potential distance that a ball will travel. Answer: In the picture below on the left the ‘goalkeeper’ has kicked the ball with less follow through (punt). Where as American football player has followed through with their hit. Answer: Question How can spreading a particular force over a greater amount of time be beneficial to a person/ athlete? Discuss this with specific examples: IB Sports, Exercise and Health Science Topic 4: Biomechanics IMPULSE PAST PAPER QUESTION Q1 Q1a Q1b A study was undertaken of Asafa Powell during his 100m sprint for a world record of 9.74s in Italy in 2007. The graphs below represent the impulse recorded from a single footfall (from first contact to the foot leaving the ground). Each graph represents a different stage of the sprint. Define the term impulse. (1) Net impulses are a combination of positive and negative impulses. Describe the net impulse during the 100m sprint for each of the following stages: (1) i. Early Stage (1) ii. Middle Stage (1) iii. Final Stage (1) IB Sports, Exercise and Health Science Topic 4: Biomechanics Q1c Compare the acceleration of Asafa Powell in the early stage to the final stage of the 100m sprint. (2) Q1d Usain Bolt, the winner of the 100m sprint at the 2008 Olympics, reaches his peak velocity later in the sprint than Asafa Powell. Using the information above, predict how Usain Bolt’s middle stage force-time graph would be different from Asafa Powell’s for the 100m sprint. (2) IB Sports, Exercise and Health Science Topic 4: Biomechanics Part B: Velocity: Force-Time graph for a Vertical Jump Define Impulse: _____________________ The diagrams below show the vertical ground reaction force during the take-off phase of a vertical jump. Examine the curve and explain what is happening to the jumper at points A, B, C, D, E and F. (8 marks) Answer: IB Sports, Exercise and Health Science Topic 4: Biomechanics Investigation: Impulse and Impacts Look at the two graphs in figure 1.1 of Force of impact against time for a baseball bat striking a ball. 1.1 Force of impact against time for a baseball bat striking a ball. A Force acting on the ball without follow through. ball with follow through. B Force acting on the 1. Explain why follow-through increases the outgoing velocity of the ball. Answer: IB Sports, Exercise and Health Science Topic 4: Biomechanics Impulse and Impacts: A worked Example THE FORCE EXERTED DURING A FOOT STRIKE DURING A SPRINT RACE This example looks at the vertical force exerted on average by a sprinter’s foot on the track during a 100m sprint. The aim of the calculation will be to estimate the reaction force produced by a foot contact - which would be the actual force produced by the runner on the ground. Consider Figure 1.2 as graphs of force against time for reaction force only (A), and net force (B). Figure 1.2 Vertical forces acting on a runner’s foot. A. Force-time graph for a single foot contact. B. Force-time graph of net force. For a male world class 100m sprinter whose time is 10.00s, and whose average stride length is 2.6m, there are 38.5 strides during the race, and the average time between foot contacts would be 10.00 = 0.26s. 38.5 The graph shown in figure 1.3 (next page) shows the path of the runner’s centre of mass against time for two complete strides. It is estimated that between one fifth and on quarter of the time between complete strides (0.06s) is that during which a foot is in contact with the ground. Note that in figure 1.2 above - this corresponds with the time for which force is applied by a foot on the ground. In between foot contacts during the unsupported part of the stride, the athlete will fall towards the ground. IB Sports, Exercise and Health Science Topic 4: Biomechanics Figure 1.3 Path of a sprinter’s centre of mass during two complete strides. Immediately after a foot leaves contact, the athletes centre of mass will be moving upwards, then rising towards a maximum height at half stride, and falling towards the next foot contact at an acceleration produced by gravity (of g = 10 ms-2). Therefore during 0.26 0.06 = 0.20 seconds, the athlete’s centre of mass will rise towards its peak, then fall again towards the ground (ready for the next foot contact). Graphs X,Y and Z (Figure 1.4) show the horizontal ground reaction force versus time traces for three situations during a 100 metre sprint race. Figure 1.4 Horizontal ground reaction force versus time in a 100 m sprint. Note: Positive forces act on the runner in the direction on the run. Question: Explain how you can tell that graph X represents the horizontal force acting on the runner during a foot contact just after crossing the finish line. (6 marks) Answer: IB Sports, Exercise and Health Science 4.3.8 Topic 4: Biomechanics Explain how Newton’s three laws of motion apply to sporting activities. Define Newton’s Third Law of Motion: Answer: IB Sports, Exercise and Health Science Topic 4: Biomechanics LAW OF CONSERVATION OF MOMENTUM Define Newton’s Law of Conservation of Linear Momentum: Answer: Individual Activity: Conservation of Momentum in American Football Answer the following questions from the video http://www.nsf.gov/news/special_reports/football/newtonthirdlaw.jsp 1.Write the formula for the Conservation of Linear Momentum: 2. What is the difference between an elastic and inelastic collision 3. Which type of collision is more common in sport? 4. What are they effects of inelastic collision on an American football player? Calculating linear momentum A golfer swings a 0.35 kg club at 30 m/s to hit a 0.04 kg ball off a tee. After impact, his club speed drops to 25 m/s. Before impact Club momentum + Ball momentum = Total momentum After impact Club momentum + Ball momentum = Total momentum IB Sports, Exercise and Health Science 4.3.3 Topic 4: Biomechanics Define the term centre of mass. Centre of Mass 1. What effects do changes in body position have on the location of the centre of mass? Position of centre of mass changes as body position changes. Answer: 2. How does the jumper change the position of his/her centre of mass relative to the centre of his/her torso during the jump? Path of centre of mass in a high jump. Answer: 3. What is so important about the centre of mass being below the bar when the athlete jumps over the bar? Answer : 4. Explain how the position of the centre of mass can lie outside the mass of a body and give examples from sport of when this is the case. Answer : 5. Explain why a handstand is a more demanding balance than a headstand. Answer: IB Sports, Exercise and Health Science 4.3.5 Topic 4: Biomechanics Distinguish between 1st, 2nd and 3rd class levers. Part A: Levers A lever is basically a rigid structure, hinged at some part and to which forces are applied at two othe rpoints. A lever consists of three parts (as defined above). What are they? 1. 2. 3. Functions Levers perform two main fucntions: What are they? 1. 2. Classes of Lever There are three types of lever systems. Define these below and provide examples of them in action: Class 1st 2nd 3rd Illustration Definition Example IB Sports, Exercise and Health Science Topic 4: Biomechanics 1. Label all the levers below: IB Sports, Exercise and Health Science Topic 4: Biomechanics Part B: Levers in the Human Body Class Example in the body INDIVIDUL ACTIVITY – LEVERS IN SPORT Identify the effort, fulcrum and load in the examples given below 1. Triceps-elbow joint 1. The action occurring at the triceps/ elbow joint. Effort (agonist): Load (resistance): Fulcrum (axis): Class of lever: Bones involved: Name the antagonist muscle: Example in sport IB Sports, Exercise and Health Science Topic 4: Biomechanics 2. Calf-ankle joint Effort (agonist): name the antagonist muscle: Load (resistance): Fulcrum (axis): Class of lever: Bones involved: A second-class lever is a type of lever in the human body; one example is the Achilles tendon, pushing or pulling across the heel of the foot. Such connections between joints, called synovial joints, are fulcrums, the bones they connect are levers, and the muscles attached to them apply force (or resistance). The body acts as second-class lever when one engages in a full-body push-up. The foot is the fulcrum, the body weight is the resistance, and the effort is applied by the hands against the ground. 3. Biceps-elbow joint 1. The action occurring at the biceps/ elbow joint. Effort (agonist): name the antagonist muscle: Load (resistance): Fulcrum (axis): Class of lever: Bones involved: IB Sports, Exercise and Health Science 4.3.9 Topic 4: Biomechanics State the relationship between angular momentum, moment of inertia and angular velocity Part A: ANGULAR MOMENTUM 1. Why is angular momentum important in figure skating? Answer: 2. What is the relationship between angular momentum and angular velocity? Answer: 3. How can vertical velocity be increased during a take off? Which Laws of Motion does this refer to? Answer: 4. What is the relationship between the position of the arms and the rotational velocity? Answer: 5. Which Law of Physics does the following principle refer to? (see picture) Answer: IB Sports, Exercise and Health Science Topic 4: Biomechanics ANGULAR KINETICS Part B: Angular Momentum Moment of Inertia and Angular Velocity Because all levers produce rotation around an axis, they also produce torque. Torque is defined as ___________________. A force that does not pass through the centre of gravity of the body on which it acts or through a point at which the body is fixed. Such a force produces translation and rotation. Its rotatory effect is known as torque. 1.How can we apply this to sporting situations when we consider how we cause a ball to spin. Consider volleyball and how we apply topspin, or backspin. Where do we hit the ball? Draw in the force, the COG and resulting rotation from topspin and backspin force on a volleyball. 2. What can we do to make the ball spin faster? So basically the greater the force applied, the greater the ____________________. The longer the lever used, the greater the _____________________. See http://protabletennis.net/content/topspin-and-backspin IB Sports, Exercise and Health Science Topic 4: Biomechanics Linear vs Angular Kinematics: Fill in Angular motion on the comparison table. Linear Motion Angular Motion Acceleration Angular acceleration Velocity Displacement Momentum Force Torque Inertia Newton’s second law Can you rewrite Newton’s 3 Laws to make them applicable to angular motion? Law Explanation IB Sports, Exercise and Health Science 4.3.10 Topic 4: Biomechanics Explain the concept of angular momentum in relation to sporting activities Conservation of angular momentum in a pike dive If a person or object such as a ball is spun they will continue to spin provided that there is no force(s) acting to stop this. Frequently forces such as friction act on us and slow the spinning down – however in instances such as during the rotating/ somersaulting of gymnasts or divers – the air resistance in these activities is actually quite small that it is nearly negligible. Also, when a person has jumped into the air they are unable to change their angular momentum as there is nothing for them to push against. This means that the persons angular momentum is conserved (stays the same) during the flight involved in their action. Fill in the blanks using key terms from the word bank: Moment of _____________________and angular velocity interrelate in _____________ movements because angular momentum is _______________ when an athlete is off the ground, or near to constant when on a surface with low _________________ eg ice skating rink). As angular momentum is constant when airborne, moment of inertia and angular velocity are _____________ As one ____________________ the other______________________. . increases friction aerial proportional inversely Inertia constant decreases Delete the incorrect option below: When the mass is moved closer to the axis of rotation, the moment of inertia increases/decreases, and the angular velocity increases/decreases. This means that the object spins faster. IB Sports, Exercise and Health Science Topic 4: Biomechanics When the mass is moved further from the axis of rotation, the moment of inertia increases/decreases, and the angular velocity increases/decreases. This means that the object spins slower. Conservation of angular momentum in a somersault: In the spaces provided discuss what happens to moment of inertia and angular velocity for each of the body positions. Angular momentum = Moment of inertia X Angular velocity Conserved throughout the flight time irrespective of body position. BODY POSITION OF ATHLETE Tucked Long ???????????? ????????????? ???????????? ????????????? The illustration below shows the interrelationship between angular velocity, moment of inertia and angular momentum. IB Sports, Exercise and Health Science Topic 4: Biomechanics a. In biomechanical detail, explain the relationship that occurs between moment of inertia and angular velocity as the diver executes the tucked backward one and a half dive. (6 marks) Answer: b. Explain why angular momentum remains constant throughout the dive? (1 mark) Answer: c. Let us assume that the diver over-rotates in the dive. Explain biomechanical detail what may have happened in order for this to occur. (2 marks) Answer: In biomechanical terms, explain why a gymnast must tuck tightly when performing a triple somersault. The tuck reduces the moment of inertia ( and as angular momentum is conserved in airborne activities ) thereby increasing the angular velocity and allowing the gymnast to spin quickly and complete the three rotations. For the landing, why does the gymnast performing a triple somersault straighten the body ? Straightening the body increases the moment of inertia thereby slowing the speed of rotation and allowing the gymnast to land without over rotating and falling over. IB Sports, Exercise and Health Science Topic 4: Biomechanics Conservation of momentum Past Paper Questions 1. Why do shot-putters use either the glide or a spin technique prior to the release of the shot (4 marks) Answer: 2. Explain how a gymnast can alter the speed of rotation during flight. (7 marks) Answer: IB Sports, Exercise and Health Science 4.3.12 Topic 4: Biomechanics Outline the Bernoulli principle with respect to projectile motion in sporting activities FLUID DYNAMICS Define the following key terms Key term Fluid Drag Surface drag Form drag Wave drag Boundary layer Bernoulli’s principle Magnus effect Definition Example IB Sports, Exercise and Health Science Topic 4: Biomechanics Question: Explain why golf balls have dimples. Answer: IB Sports, Exercise and Health Science Topic 4: Biomechanics Magnus Effect Explain Roberto Carlos swerving free kicks with regards to the Magnus Effect. http://www.real-world-physics-problems.com/physics-of-soccer.html Answer: