BIOMECHANICS MECHANICS OF MOVEMENT

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BIOMECHANICS (MECHANICS OF MOVEMENT)

• YOU NEED TO LEARN ABOUT 4 AREAS IN THIS ORDER OF
  IMPORTANCE

1. Force
2. Centre of Mass Stability
3. Motion
4. Newtons Laws
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1. FORCE

• 3 factors effect force
• Size of Force (the harder you hit a tennis ball
  the faster it will go)
• Direction of Force (if you hit the ball towards
  the net, thats the way it will go!)
• Position of Application (SPIN! if you hit the
  top of the ball in tennis it will topspin)

YOU MUST REMEMBER THESE AND BE ABLE TO APPLY
THEM TO SPECIFIC SPORTING EXAMPLES
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FORCE
Motion and Movement - Newtons Laws

• FORCE
• FORCE is push or pull
• the unit is the NEWTON (10 N is approx the weight
  of 1 kg)
• force changes the state of motion of an object
• force causes acceleration or deceleration or
  change of direction
• the more force the bigger the acceleration
• force changes the shape of an object
• WEIGHT
• FRICTION
• REACTION FORCES
• AIR RESISTANCE / FLUID FRICTION
• all these forces affect the sportsperson

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The EFFECTS of FORCE
Motion and Movement - The Effects of Force

• EFFECTS of FORCE
• force causes linear acceleration or deceleration
• including change of direction
• the point of action of a force affects what
  happens
• friction acts at the feet of a sportsperson, not
  enough of it and the persons feet slip
• if a force acts through the persons centre of
  mass (CofM), then linear motion is caused
• if a force acts to one side of the CoM then
  rotation is caused
• like take-off in the high jump, the reaction
  force acts to one side of the CoM

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2. CENTRE OF MASS
Motion and Movement - Centre of Mass

• CENTRE of MASS (CoM)
• this is the single point in a body which
  represents all the spread out mass of a body
• the weight acts at the CoM since gravity acts on
  mass to produce weight

• Relationship between Centre of Mass Application
  of Force
• The direction of the application of a force in
  relation to the centre of mass will determine
  whether subsequent motion of a body is linear or
  angular
• Linear Motion ? occurs if force applies through
  centre of gravity (e.g. vertical jump)
• Angular Motion ? occurs if line of action of
  force passes outside bodys centre of mass

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CENTRE OF MASS
Motion and Movement - Centre of Mass

• WHERE IS THE CENTRE OF MASS?
• position of centre of mass depends on shape of
  body
• this is how the high jumper can have his CoM pass
  under the bar
• but he could still clear the bar

• BALANCE
• to keep on balance the CoM must be over the
  base of support

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2. CENTRE OF MASS - STABILITY

• A number of factors effect the stability of an
  object.
• To be in a state of balance the centre of gravity
  must be
• over the base of support
• e.g. a gymnast doing an inverted balance (i.e.
  handstand or headstand) is more/ less stable
  depending on
• Height of centre of mass (by tucking legs in
  (s)he is more stable)
• Base of support (the wider the base the more
  stable a headstand is more stable than a
  handstand because it has 3 POINTS)
• Mass of the gymnast (heavier normally means less
  stable unless base of support is very wide)
• Once the line of gravity falls outside the base
  of support the gymnast will become off balance
  and fall over

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3. MOTION

• Motion is movement divided into 3 main
  categories
• Linear Motion
• Angular motion
• Linear Motion When a body moves in a straight or
  curved line, with all its parts moving the same
  distance in the same direction, at the same speed
• e.g. tobogganist or shot put
• Angular Motion When a body or part of a body
  moves in a circle or part of a circle about a
  particular point called the axis of rotation
• If the line of action of the force passes outside
  the bodys centre of mass, the resulting motion
  will be angular (this is created by an eccentric
  force a trampolinist does a forward somersault
  by leaning forward to put CoM infront then
  applying force to the bed whose reaction force
  passes behind their CoM causing them to rotate
  forwards)
• e.g. bicycle wheel turning or a door opening on a
  hinge
• e.g. athletes spinning, circling, turning
  somersaulting
• Also, the limbs move around our joints which are
  fixed points (consider flexion and extension of
  your elbow joint)
• Examples of angular motion from sport
• Angular motion of arm in front crawl in swimming
• Angular motion of whole body in giant circle of
  high bar in gymnastics
• General Motion
• Most movements in sport combine linear angular
  motion

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4. NEWTONS FIRST LAW of MOTION
Motion and Movement - Newtons Laws
INERTIA

• NEWTONS FIRST LAW
• this law is used when ZERO NET FORCE is applied
  to an object
• this doesnt mean that zero force acts, but that
  all forces MUST CANCEL OUT
• with zero net force an object
• is STATIONARY or
• moves at CONSTANT SPEED in the SAME DIRECTION
• a sprinter in full stride has four forces acting
• but they cancel out exactly
• therefore he / she travels at constant speed
• A BODY CONTINUES IN A STATE OF REST OR UNIFORM
  MOTION UNTIL ACTED UPON BY AN EXTERNAL FORCE
• E.G. FOOTBALL STAYS ON PENALTY SPOT UNTIL
  EXTERNAL FORCE OF MUSCLES KICK IT AT GOAL!

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NEWTONS SECOND LAW of MOTION
Motion and Movement - Newtons Laws

• NEWTONS SECOND LAW
• this law is used when a NET FORCE acts on an
  object
• net force FORWARDS produces ACCELERATION
• net force BACKWARDS produces DECELERATION
• net force SIDEWAYS produces CHANGE OF DIRECTION
• the bigger the force the bigger the acceleration
• the sprinter slows down at the end of a race
• there is a net force backwards
• so the sprinter decelerates
• THE HARDER YOU HIT SOMETHING THE FASTER IT
  TRAVELS
• E.G. HARDER YOU HIT A TENNIS BALL THE FASTER IT
  ACCELERATES OFF THE RACKET

ACCELERATION
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NEWTONS THIRD LAW of MOTION
Motion and Movement - Newtons Laws

• NEWTONS THIRD LAW
• this law is used when two bodies EXERT FORCES ON
  ONE ANOTHER
• ACTION AND REACTION ARE EQUAL and OPPOSITE IN
  DIRECTION
• action of jumper down on ground reaction of
  ground up on jumper
• the harder you push down on the ground, the more
  the ground pushes up on you
• this upward force on the jumper is the force
  acting to cause the take off
• FOR EVERY ACTION THERE IS AN EQUAL AND OPPOSITE
  REACTION
• E.G. A SPRINTER PUSHES INTO BLOCKS AT BEGINNING
  OF 100M RACE AND THE BLOCKS PUSH SPRINTER BACK
  OUT IN OPPSOITE DIRECTION

REACTION
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EXAMPLE QUESTIONS

• Explain how an athlete can use their knowledge of
  balance to achieve the most effective sprint
  start (3 marks)
• It is helpful for a gymnast to understand the
  influence of the centre of mass when performing a
  balance. Using a named balance, describe the
  factors that would effect performance. (4 marks)
• The application of force is essential to maximise
  performance. Using a physical activity of your
  choice, explain how an understanding of force can
  improve performance. (4 marks)
• The effect that a force has when applied to a
  sports performer can determine the type of motion
  produced. In each case, use an example from PE to
  show how you would produce (a) linear motion (b)
  angular motion. (4 marks)
• Using examples from your practical activities,
  explain how knowledge of Newtons Laws of Motion
  would improve performance. (3 marks)