BIOMECHANICAL MOVEMENT

• newtons laws of motion

  1st = law of inertia

  2nd = law of acceleration

  3rd = law of action and reaction
• newtons first law of motion

  law of inertia

  everybody stays in its state of rest or motion until a force changes it
• example of newtons law of inertia

  a footballer contracts their muscle to apply a force to the ground to move from stationary to moving towards the ball in a penalty kick
• newtons second law of motion

  law of acceleration

  acceleration is directly proportional to force and indirectly proportional to mass

  force = mass x acceleration
• example of newtons law of acceleration

  a footballer will apply more force to the ground to move towards the ball quicker
• newtons third law of motion

  law of action and reaction

  to every action there is an equal and opposite reaction
• example of newtons law of action and reaction

  at the start of a sprint, the athlete pushes back on the block as hard as possible (action), and the blocks push forward on the athlete (reaction) providing forward acceleration on the athlete
• speed

  rate of change of position

  speed (m/s) = distance covered (m) / time taken (s)
• distance

  length of the part a body follows when moving from one position to another

  distance = speed x time
• momentum

  product of mass and velocity

  mass x velocity
• impulse

  how long you apply a force for (N/s)

  force x time
• centre of mass

  point in the body at which the force of gravity can be through to act
• factors affecting stability

  height of the centre of mass

  position of the line of gravity

  area of support base

  mass of performer
• height of the centre of mass affecting stability

  lowering the centre of mass will increase stability
• area of support base affecting stability

  the more contact points, the larger the base of support becomes and the more stable the body become
• position of the line of gravity affecting stability

  should be central over the base of support, to increase stability
• mass of performer affecting stability

  the greater the mass, the more stability there is because of increased inertia
• levers 


  consists of a fulcrum, resistance and an effort

  the bones act as fulcrums, the effort is provided by the muscle and the resistance is the weight of the body part that is being moved
• three types of levers

  first

  second

  third
• first class lever

  fulcrum is located between the effort and the resistance

  e.g. the neck
• second class lever

  resistance is located between the effort and the fulcrum

  e.g. plantar flexion of the ankle
• third class lever

  effort is located between the resistance and the fulcrum

  e.g. hip, knee and elbow flexion
• mechanical advantage

  occur when the effort arm is longer than the resistance arm

  this means that the lever system can move a large load over s short distance, and requires little effort

  however it has a small range of movement and it is difficult to generate speed and distance
• mechanical disadvantage

  occurs when the resistance arm is longer than the effort arm

  this means that the lever system cannot move as heavy a load but can do it faster

  it also has a large range of movement
• second class lever - mechanical advantage and disadvantage

  advantage - can generate much larger forces. Has to lift the whole body weight

  disadvantage - slow, with a limited range of movement
• third class lever - mechanical advantage and disadvantage

  advantage - large range of movement, and any resistance can be moved quickly

  disadvantage - cannot apply much force to move an object
• internal force

  applied when our skeletal muscles contract

  • for example, the force generated as the quadriceps contract concentrically to extend the knee in a jump
• external force

  comes from outside the body

  • for example, friction, air resistance and weight
• weight and gravity

  weight is the gravitational force that the earth exerts on a body, pulling it towards the centre of the earth, or downwards

  the greater the mass of the individual, the greater the weight force pulling the body downwards

  weight = mass x acceleration due to gravity
• two types of friction

  static

  sliding
• static friction

  occurs before an object starts to glide
• sliding friction

  when friction acts between two surfaces that are moving relative to one another, sliding friction occurs
• friction

  acts in opposition to motion

  e.g. when a runners foot lands on the ground, the foot is stationary on the ground

  the direction of the frictional force changes as the body moves over the foot

  when the foot is in front of the body, the frictional force is backwards to stop it moving over the ground

  when the foot is behind, the frictional force is forwards to stop the food moving backwards

  an arrow is drawn in the opposite direction to this slipping
• factors affecting friction

  the surface characteristic of the two bodies in contact

  • spikes on a track helps to increase friction minimising slipping

  the temperature of the two surfaces in contact

  • increasing temperature reduces friction (e.g. in curling)

  the mass of the objects that are sliding

  • a larger mass results in greater friction
• air resistance

  opposes the motion of the body travelling through the air
• air resistance depends on

  velocity of the moving body

  • faster the performer moves, the greater air resistance

  cross-sectional area of the moving body

  • the larger the cross-sectional area, the greater the air resistance

  the shape and surface characteristics of a moving body

  • a streamlined shape results in less resistance, as does a smooth surface