chapter 5 biomech

• scalar quantity

  measurements described in size or magnitude - mass, distance and speed
• vector quantity

  measurements described in size and direction - weight, accelaration, displacement, velocity and momentum
• mass


  quantity of matter the body possesses
• weight

  gravitational force exerted on an object
• mass (g) x gravity (9.8) = weight (newtons)
• distance

  path a body takes as it moves from the start to the finishing position
• displacement

  shortest route in a straight line between the starting and finishing position
• speed (m/s) = distance covered (m) / time taken (s)
• velocity (m/s) = displacement (m) / time taken (s)
• acceleration

  rate of change of velocity, when velocity increases, positive acceleration occurs and when velocity decreases, negative acceleration occurs
• acceleration = change in velocity (m/s) / time (s)
• change in velocity = (final velocity)-(initial velocity) / time
• momentum (kgm/s) = mass (kg) x velocity (m/s)
• larger mass with high velocity results in a greater momentum, momentum can be conserved
• 2 types of force that can act on a performer:

  1. internal force
  2. external force
• internal force


  applied when skeletal muscles contract, e.g force generated from quads contracting concentrically to extend the knee in a jump
• external force


  comes from outside the body such as air resistance and weight
• both internal and external forces act on a performer during linear motion
• vertical forces


  gravity and weight
• horizontal forces


  friction and air resistance
• vertical force - weight


  mass x accelaration (newtons)

  gravitational force that the Earth exerts on a body, pulling it towards the centre of the Earth, greater the mass means a greater weight
• vertical force - reaction force


  occurs when 2 bodies are in contact with one another during Newton's third law
• horizontal force - frictional force


  two types:

  1. static
  2. sliding
• horizontal force - frictional - static force


  force exerted on one surface by another where there is no motion between the 2 surfaces, occurs before an objects start to slide e.g surface of the court and a shoe, dry friction with no movement
• horizontal force - frictional - sliding force


  when 2 bodies are in contact with each other and may have a tendency to slip/slide over each other
• friction acts opposite to motion
• factors affecting friction

  • surface characteristics of the 2 bodies in contact, e.g 100m runner wearing spikes to help increase friction and contact with the track to maximise accelaration
  • temperature of the 2 surfaces in contact, e.g sweeping in curdling raises the temperature of the ice to reduce friction with the stone
  • mass of the objects sliding, larger mass leads to larger friction
• horizontal force - air resistance


  force that acts in the opposite direction to the motion of a body travelling through the air
• air resistance depends on:

  • velocity of the moving body, the faster they are the greater the AR
  • cross-sectional area of the body, the larger the body the larger the AR
  • shape and surface characteristics of the body, streamlined shape and smooth surfaces result in less resistance
• net force


  resultant force acting on a body when all forces have been considered, balanced and unbalanced forces
• balanced force


  2 or more forces acting on a body that are equal in size but opposite in direction, when standing, the weight force and reaction force are equal in size but in opposite direction, so there is 0 net force and 0 change in motion
• unbalanced force


  force acting in one direction on a body is larger than a force acting in the opposite direction, when jumping the performer accelerates upwards as the reaction force is bigger than the weight force
• impulse


  = force x time

  time taken for a force to be applied to an object or body, increase in impulse will result in an increase in the rate of change of momentum, causing a larger change in velocity
• momentum


  mass x velocity
• net impulse


  a combination of positive and negative impulses
• angular motion


  movement of rotation around a fixed point
• angular motion can take place along 1 of 3 axes:

  • transverse (somersault)
  • sagittal (cartwheel)
  • longitudinal (ice skating spin)
• angular motion occurs as a result of a torque, which causes and object to turn about its axis of rotation, increasing the size of the force increases torque, applying the force further away from the axis of rotation also increases torque
• torque


  rotational consequence of force
• movement of force or torque = force x perpendicular distance from fulcrum