AN INTRODUCTION TO BIOMECHANICS

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 (Newtons 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
Stopping
Running
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Basic movement patterns
9
Biomechanical principles associated with basic
movement patterns
10
Tennis
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Biomechanical principles associated with tennis

• 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

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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

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• 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)

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• 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