Biomechanics

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Biomechanics

• The study of forces and their effects on the
  human body
• Year 11 Achievement Standard 1.2

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Characteristics of motion

• Linear motion
• Motion that occurs is a straight line. All parts
  of the body move in the same direction and at the
  same speed (e.g. jumping up in the air to catch a
  ball or travelling in a car).

Line out jumper in Rugby Union
Drag Racing
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Characteristics of motion

• Angular motion
• Motion that occurs around an axis. This axis can
  be internal (e.g. body parts rotating around a
  joint) or external (e.g. spinning a ball on your
  finger).

Spinning a ball on your finger
Spinning figure skater
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Characteristics of motion

• General Motion
• A combination of linear and angular motion. This
  is the most common of all movements, as most
  human movement requires the rotation of body
  parts around joints (e.g. cycling, swimming and
  running).

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Characteristics of motion

• Apply your knowledge!
• Classify the following physical activities as
  linear motion or angular motion or general
  motion.
• Sprinting
• Rebounding a basketball
• Driving a car
• Tossing a underhand ball in basketball
• Horse riding
• Lawn bowls

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Centre of gravity

• Centre of gravity can be defined as the single
  point at which all parts of an object are equally
  balanced.
• For a normal human being standing upright,
  their centre of gravity lies around the area of
  their navel.
• A persons centre of gravity can change depending
  on their body position because as mentioned
  before, the centre of gravity is the exact point
  where all parts of an object are equally
  balanced.
• The centre of gravity can also lie outside an
  object, especially if the object is bent over or
  leaning in a certain direction

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Centre of gravity
Centre of gravity for a normal person
Centre of gravity
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Centre of gravity

• Centre of gravity for a person whose hands a
  stretched in the air

Centre of gravity
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Centre of gravity

• Centre of gravity outside of a persons body

Centre of gravity
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Line of gravity - The line of gravity is
important when determining the stability of an
object.

• Line of gravity is the vertical line that passes
  through the centre of gravity to the ground.
• If the line of gravity falls within the objects
  base of support (i.e. its contact with the
  ground), the object is relatively stable.
• If the line of gravity falls outside the objects
  base of support (i.e. its contact with the
  ground), the object is relatively unstable.

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Line of gravity
Line of gravity
Line of gravity
Centre of gravity
Centre of gravity
STABLE
UNSTABLE
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Base of support The object on the left is more
stable because of its relatively larger BOS

• BOS is the area within an objects point of
  contact with the ground. The larger the area the
  base of support covers, the more stable an object
  will be.

Narrow BOS
Wide BOS
BOS
BOS
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Line of gravity, BOS in relation to movement

• The line of gravity (LOG) must go outside the
  base of support to initiate or continue movement.
• The direction that the line of gravity takes
  relative to the BOS will be the direction of the
  resulting movement.
• The further away the LOG is from the BOS, the
  greater the tendency the body has to move in that
  direction. E.g. Evasive running.

Line of gravity
Top of body moves towards LOG
Direction of movement
Leg pushes against the ground
Base of support
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Centre of gravity, Line of gravity, Base of
support and Physical activity

• Apply your knowledge!
• Label the following images with the COG, LOG and
  BOS.
• Is the performer stable?

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5 Quick Questions

• Name 3 ways to ensure you are stable (use
  biomechanical terms)
• In relation to stability, what is one advantage
  of being shorter? (use biomechanical terms)
• When you do a right handed lay up, what movement
  is occurring at your right hip?
• What is the agonist muscle causing this movement?
• What is the antagonist muscle during this
  movement?

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Force

• What is a force?
• A push, pull or twist that causes movement of an
  object
• Force Mass x Acceleration
• Levers are used to apply a force

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Levers are used to apply force

• Consist of a pivot point (fulcrum) and a lever
  arm (connecting the pivot point to the
  resistance).

Downward Pressure
Resistance
Fulcrum (pivot point)
Lever arm
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Levers

• The amount of leverage a person processes is
  dependent on the length of their body, in
  particular the length of their arms and legs.
• Longer levers result in greater speed at the end
  of the lever arms this is beneficial for
  throwing and striking objects.
• Short levers can be moved with less force and at
  greater speeds this is beneficial for moving
  body parts quickly and applying strength for
  pushing, pulling and lifting objects.
• Question From this information, what can you
  assume about a shorter person in comparison to a
  taller person?

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Using Levers in Sport

• In the human body, levers are made up of the
  joints (fulcrum) and the bones that connect them
  to the objects being moved.
• Levers in the human body can be manipulated to
  improve speed and apply large forces at the same
  time
• Example Running lifting your foot and knee up
  will create a shorter lever, therefore you can
  run faster

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Newtons Laws

• When exploring the area of biomechanics and human
  movement, it is useful to look at motion through
  the observations made by Sir Isaac Newton.
• Newton was a famous seventeenth-century scientist
  who developed the three laws that govern all
  motion.

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Newtons 1st Law The law of inertia.

• A body continues in its state of rest or uniform
  motion unless an unbalanced force acts upon it.
• In other words, a body will remain at rest or in
  motion unless acted upon by a force. In order to
  get a body moving, a force must overcome the
  bodys tendency to remain at rest or inertia.
  The amount of inertia a body has depends on its
  mass.

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Newtons 1st Law The law of inertia

• This soccer ball will remain at rest, until a
  force acts on it

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Newtons 2nd Law Mass, force acceleration

• The acceleration of an object is directly
  proportional to the force causing it, is in the
  same direction as the force, and is inversely
  proportional to the mass of the object.
• When a force is applied to an object it will move
  in the direction the force was applied, and,
  depending on the size of the force and the size
  of the object, the object will accelerate
  accordingly.
• A smaller object will move faster than a larger
  object.
• A greater force will move an object faster than a
  smaller force.

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Newtons 2nd Law mass, force acceleration

• Classroom experiment
• Using the equipment you have been given, answer
  the questions in the workbook as a group

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Newtons 3rd Law action reaction

• Whenever a force is applied there is an equal
  and opposite reaction.
• If an athlete exerts a force onto the ground in
  order to push off, the ground will exert an equal
  and opposite force on the athlete, pushing them
  up into the air.
• The first force of the athlete pushing into the
  ground is called an action force. The second
  force is called the reaction force (when the
  second body applies an opposing force back).

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Newtons 3rd Law action reaction
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Force summation

• To give an object momentum in activities such as
  throwing, kicking or striking an object, the
  amount of momentum given to the object is
  determined by the sum of all forces generated by
  each body part (i.e. Force summation).
• To gain maximum momentum, the force needs to be
  generated by
• Using as many segments of the body as possible.
• In the correct sequence, using large muscles
  first and then the smallest muscles last but
  fastest.
• With correct timing.
• Through the greatest range of motion.

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Application of force summation free-throw shot
technique

• In order to maximise power and efficiency of the
  shot, the whole body is used.
• Your body does not move all at once.
• The shot begins with the movement of the legs,
  pushing into the ground.
• The force is then returned back up the legs, up
  to the shoulders, down the forearms right to the
  release of the ball at the fingertips.

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Application of force summation free-throw shot
technique
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Projectile motion

• As soon as an object is thrown it becomes a
  projectile.
• A projectile is influenced by the principles that
  govern projectile motion gravity, air
  resistance, speed height, and angle of release.

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Speed, height angle of release

• Different angles of release affect the distance
  travelled and the height attained by an object.
• When a ball is released from ground level, the
  optimal angle for release for maximum distance is
  about 45 degrees
• The height of release is important when
  propelling an object anywhere higher than ground
  level. If an object needs to clear something
  higher than ground level (e.g. The cross bar on a
  goal post), the angle needs to be greater then 45
  degrees.

Angle of release
90 degrees
45 degrees
0 degrees
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Height of release

• The height an object is released with determine
  the distance the object travels
• e.g.