Principles of Biomechanics

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• Principles of Biomechanics

Reaction
Action
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Lesson Aim

• To critically examine the biomechanical
  principles which are important in Physical
  activity Sport.
• To be able to state why these principles are
  important to consider in terms of athletics.

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Outline

• Newtons Laws
• Balance and Stability
• Levers
• Force Summation
• Projectile Motion

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Newtons First Law of Motion

• every body continues in it state of rest or
  motion in a straight line unless compelled to
  change that state by external forces exerted on
  it. (conservation of momentum)

This external force will act to change the
vertical motion, but not the horizontal
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Newtons Second Law of Motion

• the rate of change of momentum (acceleration) of
  a object is proportional to the force causing it
  and the change takes place in the direction in
  which the force acts.

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Newtons Third Law of Motion

• for every force that is exerted by one body on
  another, there is an equal and opposite force
  exerted by the second body on the first (action -
  reaction)

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Balance
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Balance C-o-M

• The point about which the bodys mass is evenly
  distributed is referred to as the Centre of Mass
  (CoM)
• This is also sometimes referred to as the Centre
  of Gravity, but this actually refers only to the
  vertical direction.

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Balance C-o-M

• The location of the CoM depends on the location
  of the body segments
• Raise your arms above your head and your CoM
  rises within your body
• Lift one arm and one leg out to the side, and the
  CoM will move towards that side

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Balance C-o-M

• Understand the effect of positioning/moving limb
  segments while in the air
• if both of these people are the same height, have
  the same build and jump the same height, which
  one is going to hit the volleyball at the
  greatest height? Why?

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Balance Base of support

• The area that a body is in contact with a solid
  surface
• Base of support can be between to or more points.

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Balance unbalanced

• A body becomes unbalanced when the centre of mass
  moves outside the base of support.
• sometimes it is more valuable in athletics to be
  off balance, when why?

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LEVERS
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Levers

• a bar, hinged/pivoted at one point, to which
  forces are applied at two other points
• Fulcrum/axis
• Weight/resistance
• Force

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Levers functional aspects
Increase Speed Increase Force
First Class
Second Class
Third Class
Force arm lt Resistance arm Force arm Resistance arm Force arm gt Resistance arm
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Most levers in the body are 3rd class

• were built for speed, not force!

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Force Summation
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Inter-segment Sequencing

• when the second segment reaches its maximum
  angular velocity (zero acceleration) during the
  midrange of its motion, it too decelerates and
  transfers angular momentum to the next adjacent
  distal segment in the chain.
• such a sequence occurs, link by link, from large
  to small, from base to end (proximal to distal)
  until the end of the chain is reached.

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Force Summation
W
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Force Summation
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Projectile Motion
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Projectiles

• We typically look at
• Release height
• Release angle
• Release speed
• to evaluate projectile motion

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• Release angle there is an optimum angle
  depending on the release height
• Release ht landing ht ? 45?
• Release ht gt landing ht ? lt 45?
• Release ht lt landing ht ? gt 45?
• Release speed
• an increase in speed increased range
• Release height
• increased height increased range

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Magnus Effect

• if a ball spins in flight, it will drag some of
  the air close to the surface with it. This
  creates an area of high pressure and an area of
  low pressure on opposite sides of the ball
• this pressure imbalance will make the ball curve
  in flight

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• Ignoring air resistance, the flight of a
  projectile will take a parabolic path
• Horizontal velocity will be constant
• Vertical velocity will change by -9.8 m/s/s