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11 PDHPE Core 3 CQ3 Biomechanics PPT


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  • 1. Core 3 CQ3 HOW ARE BIOMECHANICAL PRINCIPLES REFLECTED IN THE WAY WE MOVE? In other words: How can physics be applied and observed in sport and physical activity
  • 2. Introduction • ‘Bio’ = life. • Mechanics = a branch of science that explores the effects of forces applied to solids, liquids and gases. What is Biomechanics? • A science concerned with forces and the effects of these forces on and within the human body • In what sports do biomechanics seem to play a big role in athlete development?
  • 3. • A knowledge of biomechanics helps us to: 1. Choose the best technique to achieve our best performance with consideration to our body shape. EG 2. Reduce the risk of injury by improving the way we move. EG 3. Design and use equipment that contributes to improved performance. EG
  • 4. For the following sports, mind map examples of how biomechanics can be used to achieve the above aims
  • 5. • MOTION (DP 1/4) • DEF: The movement and path of a body. – Can relate to bodies that are animate (living), such as golfers and footballers. – Other bodies may be inanimate (nonliving), such as bicycles and footballs. • Motion is evident in all forms of physical activity. Various aspects of motion can be analysed; a limb, a whole body or an object • 3 types of motion: linear, angular and general motion. How motion is classified depends on the path followed by the moving object.
  • 6. - LINEAR MOTION • Linear motion occurs when a body and all parts connected to it travel the same distance in the same direction and at the same speed. • EG A person who is standing still on a moving escalator or in a lift. The body (the person) moves from one place to another with all parts moving in the same direction and at the same time.
  • 7. • To determine if a body is experiencing linear motion, draw a line connecting two parts of the body; for example, the neck and hips. • If the line remains in the same position when the body moves from one position to another, the motion is linear.
  • 8. • Modifying or eliminating technique faults that contribute to any non-linear movements will improve performance. EG Excessive up and down, rotational and lateral movements will erode performance directed towards achieving the shortest, most efficient pathway. • Sprinters who rotate their arms across their bodies and swimmers who use an irregular arm pull that results in a zigzag movement pattern along the pool surface are examples of poor application of linear motion.
  • 9. Application • Watch the following videos and identify the following points. Make a summary list of the top 5 points that you consider to be fundamental to better freestyle technique 1. Recovery 2. Entry & Catch 3. Out sweep 4. In sweep 5. Press
  • 10. Video Clips Swim Stroke Explained GB&v=sYt8x_7uL48 Footage Michael Phelps – Freestyle v=ax77_hHq9Dc&feature=related Footage Michael Phelps – Butterfly Comparison
  • 11. Application • Freestyle - The main propulsive force of the freestyle stroke is the arm cycle. The legs add only 10% of total speed through the water, depending on whether you use a 2-, 4-, 6-, or 8-beat kick. The main function of the legs is to help keep the body balanced and efficient to allow the arms to do their work and keep the body moving when the arm cycle is at its weakest point. The following flow chart briefly illustrates the arm cycle: 1. Recovery Elbow leaves the water first, with a high elbow, hand relaxed directly under the elbow, trailing fingers on the water, then reach forwards to the entry position
  • 12. 2. Entry & Catch Thumb first, hand slightly cupped, reach further forwards and out (laterally) to 'catch' the water to prepare for the out sweep - dropping the shoulder (upon the reach) slightly will help in the 'catch' and also in the recovery of the other arm 3. Out sweep Press the water laterally to the body with only slight elbow flexion and begin to rotate the hand at the wrist medially 4. In sweep Press the water towards the hips through further flexion of the elbow and wrist as you feel the body being pulled over the hand 5. Press With the hand at the hip and palm facing towards the feet, press the water back by extending the arm to approximately 90% of full extension, keeping in line with the body to reduce drag. The arm is ready for the recovery, elbow first!
  • 13. - ANGULAR MOTION • When the human body/limb or object propelled move along a circular path about some fixed point (Axis of Rotation) Eg. Throwing a discus or forward somersault
  • 14. • There can be confusion when analysing sports, as often, both Linear and Angular Motion are evident simultaneously • This is sometimes referred to as General Motion • Consider: – Hammer Throw – Running – Cricket Bowling
  • 15. - KINEMATICS • Study of how fast, far and consistently a body moves. There are 6 concepts: 1. Distance: Length of path through which a body travels 2. Displacement: Length of a path between two points measured in a straight line. In what sports is displacement more evident/relevant than distance?
  • 16. 3. Speed: Measures the magnitude of the movement of a body. The time taken to cover a distance. Instantaneous speed is most applicable in team sports. Eg. But in races (Marathon), the runner with the greatest average speed will be the winner. In what sports contexts is ‘speed’ most advantageous? 4. Velocity: Measures the magnitude and direction of the movement of a body Eg. Achieving maximum velocity at impact during a golf swing, with the most accurate alignment as possible.
  • 17. 5. Acceleration: Ability to increase or decrease velocity rapidly. Many factors affect the body’s ability to accelerate as quickly as possible NB: Stride Length and Stride Frequency are critical factors in determining running success, and are specific to various events. To adjust these, changes must be made to running technique Eg. High knees in sprinting to increase stride length Analyse each runner for biomechanical advantages related to acceleration / Watch this video Faster-Speed--Acceleration-Specifics-6184728
  • 18. 6. Momentum: The product of mass and velocity. This is what often determines success in sport, and is most significant in impact or collision situations. – What will be the impact of a truck travelling at 50 kilometres per hour that collides with an oncoming car going at the same speed? – A hit-up in Rugby League is more effective if the momentum can be maximised
  • 19. – Angular momentum is affected by the length of the radius, and the centre of the mass of the object. The longer it is, the greater the angular velocity Eg. Driver (long) vs. 9 iron (short) – Complete the application from the text on Angular Momentum (Practical) Q. Explain the importance (make observations) of these 6 concepts in sport (large mind map with examples linking each for various sports)
  • 20. Motion - Summary
  • 21. • BALANCE AND STABILITY (DP2/4) • Stability is concerned with the resistance of a body to changes in its equilibrium • When a body can assume a stable position, it is in a state of balance – If the body is not moving it has static balance EG – If the body is moving it has dynamic balance EG
  • 22. Equilibrium • When a body is at rest or moving at a constant velocity, it is in a state of equilibrium State of Balance • Some sports place an emphasis on balance (Gymnastics/?) • Some sports require loss of balance (Sprint start/?) • Some sports require you to disrupt the balance of opponents (Rugby League/?) • The 2 determining factors in achieving a State of Balance is the Centre of Gravity and Base of Support
  • 23. - CENTRE OF GRAVITY • All objects experience an attraction towards the centre of the earth i.e. Gravitational Force. This provides us with our weight (On the moon our weight would be much less) • All objects have a specific point that the mass of an object or the gravitational force is concentrated towards • From this point a line can be drawn vertically which is the Line of Gravity • The Centre of Gravity does not need to lie within the physical limits of a person
  • 24. - LINE OF GRAVITY • A vertical line passing through the CoG and extending to the ground, which indicates the direction that gravity is acting on the body. When standing, it dissects the centre of gravity so that we are perfectly balanced over our base of support. • Movement occurs when the line of gravity changes relative to the base of support. Movement results in a momentary state of imbalance being created, causing the body to move in the direction of the imbalance. Eg Walking / Sprint & Swim Start • During specialised skills, athletes progressively develop a feel for the line of gravity relative to the base of support, enabling the controlled instability required for movement. • Therefore, less force is required to initiate the desired movement. EG Swimmers and sprinters on the blocks bend forward, moving the line of gravity to the edge of the base of support so that less force is required to execute the dive.
  • 25. - BASE OF SUPPORT • The region bounded by the body parts in contact with the surface, eg the area covered by your feet when standing, the area between the outer limits of your hands when you hang from a bar. • The BOS affects our stability or our ability to control equilibrium. – A narrow base of support allows the centre of gravity to fall close to the edge of the base of support. Only a small force is needed to make the person lose their balance – A wide base of support is essential for stability because the centre of gravity is located well within the boundaries. Draw a diagram to represent these principles
  • 26. • The dancer performing a pirouette has a very narrow base of support and must work hard to ensure that their centre of gravity remains within the base. • Wrestlers widen their BOS to prevent their opponents from moving them into a disadvantageous position. • Golfers spread their feet evenly to at least the width of their shoulders to enhance balance when they rotate their body during the swing.
  • 27. Stability - Summary • Overall stability depends on: 1. Where the line of gravity falls in relation to the base of support – Maximum stability is when the line of gravity falls through the centre of the base of support – Increasing the area of the base of support will increase stability 1. The Weight of the Body – The greater the mass, the greater the stability – A heavier object is more difficult to move 1. The Height of the Centre of Gravity relative to the base of support – An object with a low Centre of Gravity will be more stable
  • 28. • FLUID MECHANICS (DP3/4) • Relates to the properties of gases and liquids. • It is important because physical activities such as running, throwing and swimming all take place in fluid environments, (air, water or a combination of both). • The type of fluid impacts on performance. EG When we throw a javelin, hit a golf ball or swim in a pool, forces are exerted on the body or object AND the body or object exerts forces on the surrounding fluid. • Knowledge about how to equip ourselves and better execute movements in specific fluid environments, improves safety and can significantly enhance performance. • Watch eLesson Video on JacPlus on Fluid Mechanics
  • 29. - FLOTATION • Some people appear to float better in water than others (?). Many people are able to push and glide from the pool wall, floating momentarily but then sinking, usually feet first. Others have difficulty getting under the surface of the water during a ‘duck dive’, their feet kicking and splashing on the surface as they try to submerge. • The ability to float — to maintain a stationary position on the surface of the water — varies from one person to another. • Who can normally float the best? Why? • Flotation impacts on swimming, survival in water and even our ability to learn to swim.
  • 30. • Our body floats on water when: the forces created by its weight are matched equally or better by the buoyant force of the water. • For an object to float, it needs to displace an amount of water that weighs more than itself. Conversely, if the object displaces a quantity of water that weighs less than itself, it sinks. Hence, wearing a personal flotation device (PFD) increases buoyancy because its size displaces a lot of water with only a minimal increase in weight.
  • 31. • Body density, or its mass per unit volume, impacts on the ability to float. The density of the human body varies from one person to another. The average weight density of the human body is approximately equal to that of water. • If our weight density is high, that is, we are relatively fat free, the body sinks in water. Conversely, if we have higher proportions of less compact tissue such as fat, we tend to float. • The human body does not float evenly if left in the prone position. This is because the density of the human body (body composition) is not uniform as it is composed of different materials.
  • 32. • Diverse body tissue including bone, fat and muscle each has a specific density. Some are more dense, such as teeth and bones, whereas other parts such as lung tissue and intestines have lower densities. • Again, the distribution of organs and tissue throughout the body makes some areas less dense in comparison to others. EG The upper body contains the lungs (low density tissue), making this area less dense than the lower body, which contains a high percentage of bone and muscle. • Therefore: objects with densities higher than water sink, while those with densities lower than water float. However, it is common for people to sink non-uniformly from a horizontal, stationary floating position and this usually begins with the feet.
  • 33. - CENTRE OF BUOYANCY • Every floating object has a centre of gravity and centre of buoyancy. The centre of gravity is the point around which the body's weight is equally balanced in all directions. While differing body shapes contribute to variations in the exact location of the human body's centre of gravity, even when floating the centre of gravity is generally found about the waist • The centre of buoyancy is the centre of gravity of the fluid displaced by a floating object. Around this point, all the buoyancy forces are balanced. • The lungs, which contain a large volume of air, draw the centre of buoyancy towards the chest. The body's centre of gravity (centre of mass) is located more towards the hips and the exact position varies from one individual to another.
  • 34. • During an attempt to float, gravity pulls the lower body downwards (greater mass) while the buoyant forces push the chest and upper body upwards (less mass in this area). • The result is that the body rotates until the centre of mass lies directly below the centre of buoyancy. This leaves the body in varying degrees of diagonal positions depending on the position of the centre of mass in each individual.
  • 35. - FLUID RESISTANCE • When a body or object moves, whether it be in air or water, it exerts a force and simultaneously encounters a resisting force from that medium. • In sporting competitions such as swimming and athletics, drag and lift forces are constantly responding to the object or body's thrust. • When competitors throw objects such as the discus or javelin, or propel themselves forward, maximum length/speed is generated when drag is minimised.
  • 36. • Lift is the force that operates at right angles to the drag. • While in most activities lift is essential in keeping the implement airborne, sometimes negative lift is an advantage. • An example of using technology to create favourable negative lift is the use of an inverted wing on Formula 1 cars to maximise downforce and ultimately improve performance.
  • 37. • There are many types of forces exerted by fluids that resist an implement or body trying to move through it. • At the same time, technological improvements have enabled us to decrease resistance; EG better configuration of the dimples on a golf ball can improve its flight performance. • Drag is the force that opposes the forward motion of a body or object, reducing its speed or velocity. • It is a resisting force because it acts in opposition to whatever is moving through it.
  • 38. • Drag forces run parallel to flow direction (airflow, water), exerting a force on the body in the direction of the stream. EG Watch a swimmer push off the pool wall following a turn. Their forward motion gradually decreases due to resisting forces applied by the water, which makes the swimmer stop unless arm or leg action begins. • A body that is streamlined (contoured to reduce resistance) and technically efficient moves through the medium, creating less drag than a body that is not as streamlined.
  • 39. • The amount of drag experienced depends on a number of factors, including: 1. Fluid Density: Because water is denser than air, forward motion in this fluid is more difficult. Why is swimming in salt water easier? 2. Shape: If a body or object is streamlined at the front and tapered towards the tail, the fluid through which it is moving experiences less turbulence and this results in less resistance. A good Frisbee throw should… 3. Surface: A smooth surface causes less turbulence, resulting in less drag. Swimming attire? 4. Size of frontal area. If the front of a person or object (area making initial contact with the fluid) is large, resistance to forward motion is increased What does it feel like to swim keeping your head above water? / What happens during bodysurfing when you lift your head? – Fluid Mechanics in Swimming
  • 40. • There are two types of drag forces — surface drag and profile drag. 1. Surface drag or skin friction • Refers to a thin film of the fluid sticking to the surface area of the body or object. This layer sticks to the next layer and progressively to neighbouring layers. However, attachment to outer layers becomes increasingly weaker until there is no attachment at all. • The fluid in the immediate vicinity of the surface of a projectile comprises the boundary layer. When an object such as a discus is thrown, pockets of fluid in the boundary layer become unstable as the object moves through it. • The thrust of the object disturbs air that is in laminar flow to make way for its mass. This air is then forced to detour around the object but becomes mixed in the process. Some attaches itself to the object and even rotates with it if the object is spinning.
  • 41. • Turbulence develops, causing forces known as surface drag to be exerted on the object, causing forward movement to be slowed. • The coarser or less streamlined the surface of the object, the thicker is the boundary layer. • The air ahead of the golf ball is in laminar flow until disturbed by the advancing ball and causing the formation of a boundary layer to develop around the ball.
  • 42. 2. Profile drag • Refers to drag created by the shape and size of a body or object. • As they move through fluids, bodies or objects cause the medium to separate, resulting in pressure differences at their front and rear. • The separation causes pockets of high and low pressure to form, resulting in the development of a wake or turbulent region behind the body or object. • When we swim, for example, fluid pressure at the front of our body is greater than fluid pressure behind our feet. Objects with bigger cross-sectional areas produce more profile drag in comparison to streamlined objects which, because of their shape and smoothness, cause less drag.
  • 43. • Cyclists try to reduce profile drag by reducing the size of their frontal area (bending forward) and by ‘drafting’ or following closely behind other cyclists to reap the benefits of being in the low pressure area. • (a) has a large cross-sectional area with extensive wake at its rear. The wake has whirling currents that tend to flow up, which opposes forward motion. (b) is more streamlined, causing less interference to airflow, resulting in a smaller
  • 44. • Much has been done to minimise resistance forces that oppose movement in fluid mediums. 1. Technique. Cyclists, speed skaters and downhill skiers all bend forward at the trunk. 2. Tactics. Distance runners and cyclists follow one another closely where possible. 3. Clothing. Tight bodysuits made of special friction-reducing fabrics are worn by runners, cyclists and swimmers. 4. Equipment design. Designs of equipment such as golf balls, golf clubs, cricket bats, bicycle helmets, footballs and surfboards are continually being modified to make them more aerodynamically efficient.
  • 45. The Magnus Effect • The Magnus effect explains why spinning objects such as cricket and golf balls deviate from their normal flight paths. • When an object such as a cricket ball or golf ball is bowled or hit into the air, its spinning motion causes a whirlpool of fluid around it that attaches to the object. According to the direction of spin, the object's movement is affected. • We are familiar with three types of spin. – Topspin occurs when a ball or object rotates forward on its horizontal axis causing it to drop sharply. – Backspin is the opposite and occurs when a ball or object rotates backwards, causing it to fall slowly at the end of flight. Both topspin and backspin shorten the flight of the ball. – Sidespin refers to rotation around a vertical axis, causing the ball or object to curve left or right during flight.
  • 46. • Spinning causes the formation of pockets of high and low pressure. The size of the pressure pockets depends on the speed of rotation and roughness of the surface. • Fast bowlers shine one side of a cricket ball to enhance the streamlining effect while leaving it rougher on the other side. This assists a properly delivered ball to swing during flight as one side of the ball is able to move through the air with less resistance than the other side. • The cricket ball experiences a force towards the side of the low pressure causing it to move in that direction. Where pressure differences occur, objects always move from the area of high pressure to low pressure. CNN News report on the Jabulani - Video adidas-jabulani/2596/ Science Article about the Jabulani - Text
  • 47. • Two sports that rely heavily on backspin and topspin are tennis and table tennis. • While the surface of the table tennis ball is relatively smooth, the dimpled face of the bat allows considerable velocity to be imparted, enhancing the Magnus effect. • The comparatively rougher surface of the tennis ball enhances its ability to ‘grab’ air in the boundary layer and dip quickly when hit over the net with topspin.
  • 48. • Newton’s First Law of Motion: An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by a force • i.e. No force equals no movement • A stationary object presents a resistance to change it’s state of motion i.e. Break the inertia • This seems obvious, but is relevant when you consider the many forces that can interrupt the motion of a body • FORCE (DP4/4)
  • 49. • Newton’s Second Law of Motion: The acceleration of a body is proportional to the force causing it, and the change takes place in the direction in which the force acts • Eg. A golf ball will move in the direction it is hit and according to how hard it is hit
  • 50. • Newton’s Third Law of Motion: For every action, there is an equal and opposite reaction • When you jump in the air and land, there is a force that acts from your body towards the ground and the ground imparts a force towards the body. The effect of these equal forces is much greater on the human however; therefore, the body absorbs this force by bending the legs • When you do sprint start, you apply force to the blocks, which in turn apply a force in the opposite direction
  • 51. - HOW THE BODY APPLIES FORCE • Players are apply forces (biomechanics) to objects such as the ground to enable them to run faster, or to a tennis racquet to enable them to hit the ball harder. • In doing this, the players are confronted with opposing forces such as gravity, air resistance and friction.
  • 52. • Forces can be internal or external. – Internal forces are those that develop within the body; that is, by the contraction of a muscle group causing a joint angle to decrease (for example, the contraction of the quadriceps when kicking a football). – External forces come from outside the body and act on it in one way or another. For example, gravity is an external force that acts to prevent objects from leaving the ground • There are two types of forces — applied forces and reaction forces
  • 53. • Applied forces are forces applied to surfaces such as a running track or to equipment such as a barbell. When this happens, a similar force opposes it from outside the body. This is called a reaction force • The result is that the runner is able to propel his or her body along the track surface because the applied force generated by the legs is being matched equally by the reaction force coming from the track surface. • The greater the force the runner can produce, the greater is the resistance from the track. The result is a faster time for the distance. EG Newton's third law
  • 54. • We see evidence of the application of force in all physical activity. • Consider the following examples: the high jumper, discus thrower, cricket bowler and basketball player How effective would they be if they were suspended and had nothing to push against? Read the article on the WS and do the questions relating to cricket
  • 55. 1. Use arrows to indicate the direction of the applied force and the direction of the reaction force in the figure below 2. What would be the effect on the runner's performance if the applied force was increased? 3. Suggest how the principle of forces could be applied to the start in running, generating a more powerful long jump or winning a scrum in rugby with a lower pack weight.
  • 56. • To propel the body higher, faster, or further, we need to develop power. Power is expressed by the formula • Work = Force × Distance. • An increase in power can be achieved by 1. An increase in strength (force) 2. An increase in the speed at which muscles shorten • Both of these lead to an increase in power, but the athlete must decide which component (strength or speed of muscular contraction) is of greatest benefit
  • 57. • Some sports need to focus on rapid muscular contraction while controlling the strength aspect. This is called speed-dominated power. • In contrast, some sports need to be able to move large amounts of weight. This is called strength- dominated power • By identifying the specific requirements of the sport, the athlete can be better prepared by developing the type of power required, and training specifically to this. To what degree do the following sports require speed-dominated power OR strength-dominated power
  • 58. Summation of Forces • As a Long Jumper applies contact to the ground there is force being produced in the ankle, knee, hip and trunk i.e. When added together the total force produced is great • Summation of Forces is influenced by: – The number of body parts used – Order and timing – Force and velocity produced by the muscles
  • 59. - HOW THE BODY ABSORBS FORCE • When the body lands on a floor or similar surface, it exerts a force on the surface. In response, the surface exerts a force on the body • Forces exerted on the body are absorbed through the joints, which bend or flex in response to the impact • If we did not bend the knees and allow a slow, controlled dissipation of the forces by the muscles, the risk of injury to the joint would be increased. • EG Activities such as rebounding in basketball, landing in high jump and stopping the bounce while on a trampoline
  • 60. • In an activity such as the landing phase of a vertical jump, the muscles in the front of the thigh (quadriceps) lengthen while absorbing the force. Joint flexion helps prevent injury to surrounding tissue • Application and Inquiry: Perform two long jumps — one covering a short distance and the other, the maximal distance that can be jumped. Observe the amount of knee flexion that you experience in each of the jumps. Answer the questions on the WS
  • 61. • The body also absorbs forces while catching objects like a ball. In the process of catching, a force is exerted by the ball on the hand and a force is exerted by the hand on the ball. Catching a ball can sting if the force of the ball is not absorbed effectively • The impact felt by an object being caught is the product of: – The force of the ball (how fast it is moving) – The distance through which the hands move while receiving the ball (how much ‘give’)
  • 62. • Since the force of the ball remains constant, the only variable that can be changed is the distance through which the hands move when catching the ball • To increase the catching distance and thereby absorb the force more effectively, use the following technique: – Catching arm is outstretched. When the ball meets the hand, the arm is drawn quickly to the body. If possible, move it past and behind the body to increase the distance over which the ball is caught, by pivoting the body during the catch • An overemphasis on ‘soft-hands’ can increase the chances of a dropped catch (may have to cop pain)
  • 63. - APPLYING FORCE TO AN OBJECT • Contact forces involve actions (push or pull) exerted by one object in direct contact with another Eg. Striking a ball with you foot / Contact with the ground / Friction / Fluid Resistance (air or water) / Elastic forces (trampoline) • Non Contact forces act from a distance – there is no contact between objects Eg. Gravity • When applying force to objects, eg barbell, cricket bat or netball, there are a number of considerations
  • 64. • First, the quantity of force applied to the object. The greater the force, the greater is the acceleration of the object • A small soccer player provides little force to the ball in comparison to the same ball being kicked by a bigger player (other factors being equal)
  • 65. • Second, if the mass of an object is increased, more force is needed to move the object the same distance • For example, if a football becomes heavier as a result of wet conditions, more force is required to pass or kick it
  • 66. • Third, objects of greater mass require more force to move them than objects of smaller mass • The size of the discus, javelin and shot-put is smaller for younger students than older students. This assumes that older students have greater mass and are thereby able to deliver more force than younger students because of their increased
  • 67. • In many sports and activities, the body rotates about an axis. When this happens, 2 forces are experienced – Centripetal forces are forces directed towards the centre of a rotating body (Centre-seeking) – Centrifugal forces are directed outwards (Centre-fleeing) • The greater the speed about the axis, or the longer the axis is, the greater the force produced
  • 68. • In the golf swing and hammer throw, powerful forces are generated, allowing them to be propelled distances far greater than would be possible without body rotation. • When you go around a bend in the car, you slide towards the outside of the bend. • A cyclist leans into a corner to counter-act these forces • When a gymnast swings around a bar, there is a force driving their hands into the bar, and a force that is forcing them away from the bar • – Hammer Throw Video
  • 69. • To manage centripetal and centrifugal forces in sporting situations: – Gradually increase speed so that you learn to feel the forces and match the force exactly – Work on your balance so that you become comfortable leaning beyond where you would normally be balanced – Ensure a firm handgrip if holding an object such as a bat or high bar – Bend your knees and ensure you have good traction/grip