Biomechanics

• What is Newton’s first law of intertia?

  a body continues in a state of rest or uniform velocity unless acted upon by an unbalanced or external force
• inertia is the resistance of a body to change its state of motion
• weight = mass x gravity
• the greater the mass, the greater the inertia; some bodys have a greater inertia than others
• apply Newton’s first law to a 100 metre sprint?

  when the body is in a state of rest there is high inertia as the horizontal and vertical forces are balanced

  when the body is in state of constant velocity then there is high inertia as horizontal and vertical forces are balanced; Newton’s first law applies

  when the body is in a state of acceleration there is low inertia as the forces are unbalanced meaning this law doesnt apply
• what is Newton’s second law of acceleration ?

  a body’s rate of change in momentum is directly proportional to the size and direction of the force applied
• momentum is how much motion is achieved momentum = mass x velocity
• Inertia must be broken to achieve acceleration; body’s that achieve a larger amount of forward momentum will have a greater acceleration
• apply Newton’s second law to a sprinter?

  when pushing off the starting block, there is an action force (muscular force) and the reaction force is the block pushing down on the sprinter; this reaction force is equal to the amount of momentum and acceleration
• what is newtons third law of reaction?

  for every action force applied to a body there is an equal and opposite reaction force
• what are some examples of newtons third law?

  a high jumper needs to push down on the ground in order to go up

  if a rugby player pushes to the left with their foot then they will swerve to the right
• an action force could be the athletes weight acting downwards against the ground and a reaction force could simply be an equal and opposite force from the ground against the athlete
• what is inertia of a moving object?

  an object travelling at constant velocity has inertia and doesn’t want to change shape, direction, decelerate or accelerate

  the larger the inertia the greater the force required to change its state of motion

  the greater the mass the greater the inertia
• what are the vertical forces?

  gravity (downwards)

  action force (from muscles in a downwards direction)

  reaction force (from ground pushing up against body)
• what are the horizontal forces?

  friction

  air resistance
• what is a net force?

  when all the forces are considered the overall motion of the body can be determined
• when the net force is 0, all of the surrounding forces are balanced which suggests the object or body is in a state of inertia; the object has had no change in motion so either any rest or travelling at a constant velocity
• Reaction is the equal and opposite force exerted by a body in response to the action force placed upon it.

  Measured in newtons And a result of newtons third law; always present when two bodys are in contact
• Velocity is the rate of change in displacement

  velocity = displacement / time taken
• acceleration is the rate of change in velocity

  acceleration = (final velocity - initial velocity) / time taken
• force is a push or pull that alters the state of motion of a body

  force = mass x acceleration
• weight is the gravitational pull that the earth exerts on a body and is measured in newtons

  weight = mass x acceleration
• friction is the force that opposes the motion of two surfaces in contact; measured in newtons and has affecting factors
• what are factors affecting friction?

  roughness of ground surface; athletes run on rough rubberised tracks

  roughness of contact surface; athletes wear spiked shoes

  temperature; f1 drivers have a warm lap as friction increases as temp increases
• air resistance is the force that opposes motion through the air, it’s a form of fluid friction and measured in newtons
• what are the factors affecting air resistance?

  velocity; the greater the velocity the greater the force of air resistance

  shape; helmets that streamline to decrease air resistance

  frontal cross sectional area; lower fcsa reduces air resistance

  smoothness of surface; increased smoothness decreases air resistance
• Centre of mass is the point at which an object or a body is balanced in all directions

  body tends to be concentrated

  for a round object this is generally in the middle

  it can be more complex for human body especially when moving
• what is stability ?

  the ability of a body to resist motion and remain at rest

  also the ability to withstand a force applied and return to the original position without damage
• what factors affect stability ?

  mass of body; greater the mass the greater the inertia

  heigh of centre of mass; lower the centre of mass the greater the stability

  base of support ; greater the BoS the greater the stability; this can be increased by more points of contact

  line of gravity; the more central the line of gravity to the bos the greater the stability
• How do limb kinematics enhance sport performance?

  helps prevent injury

  assesses gait/ movement efficiency/ velocity/ acceleration and joint angles

  3D analysis of sporting action and skill technique
• what are limb kinematics?

  the study of movement in relation to time and space

  using specialist infrared cameras which digitise reflective markers placed on specific joints and landmarks on the body

  execution of technique can be measured against a perfect model
• What are force plates ?

  used in lab conditions and involves a metal plate linked to computer software which measures vertical forces

  measures weight projecting downwards as well as reaction force acting upwards and can also measure speed
• explain the phases of a standing vertical jump on a force plate graphical analysis ?

  1. flat line represents weight of performer
  2. unweighting; downward phase of vertical jump (prep phase usually in crouched position) eccentric muscle contractions are created
  3. large action force results in large reaction force; positive curve is take off phase and the larger the curve the larger the action force
  4. flight is achieved and mass= 0
  5. massive upward spikes due to weight and momentum crashing down
• what are wind tunnels?


  develop the optimum surface characteristics like streamline and frontal cross sectional area of an object

  test aerodynamic efficiency

  object is placed inside a wind tunnel with instruments to measure the forces produced by the air against its surface

  study the flow of air around object by injecting smoke into tunnel

  improves flow of air around an object; increasing lift or decreasing drag

  control environmental factors like wind speed or direction
• what is mechanical advantage ?

  where a body is able to move a large output mode with a smaller effort

  occurs when the fulcrum and load are next to each other
• what is the equation for mechanical advantage ?

  mechanical advantage = load arm / effort arm
• what is a first class lever and give an example?

  fulcrum is in middle

  throw in football; load = ball, fulcrum= elbow joint, effort= triceps brachii
• bones create the lever arm

  joints create the fulcrum

  muscles create the effort

  body weight creates load
• the difference between the effort and fulcrum is the effort arm
• the distance between the load and the fulcrum is the load arm