Biomechanics

• Biomechanics


  The study of human movement and the effect of force and motion on performance
• Biomechanics


  • Enables us to:
  • Analyse performance
  • Maximise efficiency of movement
  • Reduce overuse or acute injuries
  • Design protective, comfortable and effective equipment
• Newton's first law (law of inertia)


  A body continues in a state of rest or uniform velocity unless acted upon by an external or unbalanced force
• Inertia


  The resistance an object has to change its state of motion. The larger the object or greater the mass of the object the greater the inertia.
• Examples of Newton's first law


  • A golf ball will remain stationary on a tee with gravity acting upon it, until the golf club applies an external force to it
  • An 100m sprinter will remain at rest until an external force large enough to overcome their inertia creates motion
  • When the sprinter reaches a constant velocity, they should continue at that constant velocity until an external or unbalanced force acts upon them to change
• Newton's second law (law of acceleration)


  A body's rate of change of momentum is proportional to the size of the force applied and acts in the same direction as that force
• Examples of Newton's second law

  • The harder the golfer hits the ball and the larger the mass of the club, the further the ball will travel
  • The greater the force applied to the sprinter the greater the rate of change in momentum and therefore acceleration away from the blocks. The force is applied in a forward direction and so the sprinter drives towards the line
• Newton's third law (law of reaction)


  For every action force applied to an object there is an equal and opposite reaction
• Examples of Newton's third law

  • The swimmer pushes against the wall in a tumble-turn and the wall applies the force back to the swimmer who moves in the opposite direction of the action force
  • When a 100m sprinter applies a down and backward action force into the blocks, the blocks provide an equal and opposite up and forward reaction force to the sprinter to drive them out of the blocks
• Key concepts within Newton's Laws

  • Velocity
  • Momentum
  • Acceleration
  • Force
• Velocity


  The rate of change of displacement
• Momentum


  The quantity of motion possessed by a moving body
• Acceleration


  The rate of change in velocity
• Force


  A push or pull that alters the state of motion of an object
• Force = mass x acceleration
• Effects of force

  • Create motion
  • Accelerate a body
  • Decelerate a body
  • Change direction of a body
  • Change shape of a body
• Types of forces

  • Internal forces
  • External forces
• Net force

  The sum of all forces acting on the body
• Weight


  The gravitational pull that the earth exerts on a body measured in newtons
• Reaction force


  The equal and opposite force of the body in response to gravity
• Friction


  The force that opposes the motion of two surfaces in contact
• Factors affecting friction

  • Roughness of the surfaces in contact
  • Temperature of the surfaces in contact
  • Size of normal reaction
• Air resistance


  The force that opposes the motion of a body travelling through the air
• Factors affecting air resistance

  • Velocity of the body
  • Shape of the body
  • Frontal cross-sectional area
  • Smoothness of the surface
• Examples of friction and air resistance


  • An F1 car is designed to create minimum air resistance and maximum friction to allow the tyres to grip the track surface when cornering at high speeds
  • Drivers will swerve around on the warm up lap to increase the temperature in the tyres to increase friction, the aerofoils add down force to increase friction and the frontal cross- sectional area is minimal to reduce air resistance
• Free body diagrams

  Diagrams showing the size and direction of the vertical and horizontal forces acting on a body at an instant in time and the resulting motion
• Examples of free body diagrams

  • Diagram of a middle distance runner in motion showing air resistance, reaction force, weight and friction
• Centre of mass

  The point at which a body is balanced in all directions. Its position relies on the distribution of the body mass and can be manipulated to improve performance.
• Factors affecting stability

  • Mass of the object - the greater the mass the greater the inertia
  • Height of the centre of mass - the lower the centre of mass the greater the stability
  • Base of support - the wider the base of support the greater the stability
  • Line of gravity - is an imaginary line with extends down from the centre of mass to the floor. Keeping the line of gravity within the base of support helps to maintain stability
• Stability


  The ability of a body to resist motion and remain at rest. It is also the ability to withstand external forces.
• Effort


  (position of the insertion of the muscle)
• Load


  (the weight or resistance)
• Components of a lever system

  • Lever
  • Fulcrum
  • Effort
  • Load
• Classification of levers

  • First Class = Fulcrum
  • Second Class = Load
  • Third Class = Effort
• Load arm


  The distance between the load and the fulcrum
• Effort arm


  The distance between the effort and the fulcrum
• The greater the distance of the effort arm or load arm the more significant the effort or load becomes.
• Mechanical advantage


  The effort arm is greater in length than the load arm.
• Mechanical disadvantage


  The load arm is greater in length than the effort arm. In a third class lever the load arm is greater in length than the effort arm which means a much greater forces is required to work against a resistance.
• Linear motion


  The movement of a body in a straight or curved line where all parts move the same distance in the same direction over the same time