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CHAPTER 4

CHAPTER 4. AN INTRODUCTION TO BIOMECHANICS. Biomechanics. Biomechanics is the study of how and why the human body moves. It investigates how the physical laws of mechanics apply to the human body.

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CHAPTER 4

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  1. CHAPTER 4 AN INTRODUCTION TO BIOMECHANICS

  2. Biomechanics • Biomechanics is the study of how and why the human body moves. • It investigates how the physical laws of mechanics apply to the human body. • Role of biomechanist: analyse an athletes performance in order to improve technique, improve equipment design and reduce injuries. • Quantitative Analysis: use of numbers (eg speed / distance / time) • Qualitative Analysis: description without numbers (eg bend your knees • Checkpoints: Page 95 – Q.1,3

  3. Principles of Biomechanics • CD-ROM: • Overview • Inertia • Mass • Force • Types of forces • Newtons Laws of Motion • Velocity: (page 98) • What does velocity measure? • What are its two important characteristics? • Read: Reality PE Snapshots (Page 99) • Radar equipment!

  4. Principles (cont) • CD-ROM: • Impulse • Checkpoints: (page 102) • Questions: 1, 2, 4, 5 • Acceleration: (Newton’s 2nd law) • What is acceleration? • How do you calculate acceleration? • Conservation of momentum: (Newtons 3rd law) • What is this principle? • Give an example of how this principle works? • Elasticity: • What does the term elasticity mean? Explain two ways in which a tennis player can generate more velocity through elasticity.

  5. Principles (cont) • Summation of Momentum: • Define summation of momentum? • When does effective summation of momentum take place? • CD-ROM: • Friction • Checkpoints: (page 112) • Questions 3, 5, 6

  6. Balance and Stability • Read pages 113-118 • Define the terms Balance and Stability? • What factors affect balance and stability? • Explain the difference between static and dynamic balances? • What is meant by the ‘centre of gravity’ and how does it change when you change your body position? • How does the mass of a person affect their stability? • CD-ROM: Recap of balance using CD examples.

  7. Basic movement patterns Throwing Striking Running Stopping

  8. Basic movement patterns

  9. Biomechanical principles associated with basic movement patterns

  10. Tennis

  11. Forces Levers Torque Velocity Power Acceleration Deceleration Projectile motion Momentum Elasticity Coefficient of restitution Spin Centre of gravity Base of support Accuracy Mass Inertia Motion Impulse Biomechanical principles associated with tennis

  12. Tennis • Force (Newtons N) • A push or a pull • What effect does a force have on an object? Starts, stops, speeds up, slows down, changes direction. It changes an objects velocity • Velocity (ms-1) • displacement / time

  13. Mass (kg) • Amount of matter in an object • Weight is an indirect measure of mass • Acceleration (ms-2) - change in velocity / time - final velocity – initial velocity time

  14. Newtons laws 1. A body continues in its state of rest or of uniform motion in a straight line unless it is compelled to change that state by forces acting on it. 2. The acceleration of an object is directly proportional to the net force applied and inversely proportional to its mass. F = ma 3. For every action the is an equal and opposite reaction.

  15. Momentum • Momentum (kg ms-1) - p = mv - two objects travelling at the same velocity, the one with the greater mass will have the greater momentum and vice versa, two objects of the same mass, the one travelling at a greater velocity will have a greater momentum. - momentum is always conserved

  16. Impulse • Change in momentum • I =  p OR I = Ft • Impulse can be increased by increasing the force applied or increasing the time over which the force is applied. • When a mass is constant, a change in impulse will result in a greater release velocity of the object (ball)

  17. Summation of momentum • Used to maximise the speed of the racquet head • Works when the larger slower body parts begin the movement and move sequentially through until the smaller and quicker finish the movement. • See laboratory

  18. Elasticity • The ability of an object to return to its original shape • The more quickly an object does this the less energy it looses • Coefficient of restitution is a measure of an objects elasticity e = height bounced height dropped • String tension determines how much contact time the ball has with the racquet

  19. Levers • Classes of levers • Factors that affect the use of external levers • Length of levers • Inertia of the lever • Force • Compare and contrast techniques (elite and novice) • Evaluate performance using biomechanical principles

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