Biomechanics

• what is Newtons first law?

  a body continues in a state of rest of uniform velocity unless acted upon by an external force
• what is Newtons second law?

  a body's rate of change in momentum is proportional to the size of the force applied and acts in the same direction as the force applied
• what is Newtons third law?

  for every action force applied to a body, there is an equal and opposite reaction force
• what are Newtons laws of motion?

  1. Law of inertia
  2. Law of acceleration
  3. Law of reaction
• what is displacement?

  the shortest straight line route between the start and finish points
• what is velocity?

  the rate of change in displacement
• Velocity calculation?

  velocity (m/s) = $\frac{displacement\ \left(m\right)}{time\ \left(s\right)}$
• what is momentum?

  the quantity of motion possessed by a moving body
• Momentum calculation?

  Momentum (kgm/s) = mass (kg) x velocity (m/s)
• what is acceleration?

  rate of change in velocity
• acceleration calculation?

  acceleration (m/s/s) = $\frac{final\ velocity\ \left(ms\right)\ -\ initial\ velocity\ \left(ms\right)}{time\ taken\ \left(s\right)}$
• what is force?

  a push or pull that alters the state of motion of a body
• force calculation?

  Force (N) = mass (kg) x acceleration (m/s/s)
• what is internal force?

  skeletal muscles create force to make our joints move
• what is external force?

  factors from outside the body that act upon an object e.g. Air resistance, Friction, Weight, Reaction etc
• what is the net force?

  the sum of all forces acting on a body, it is the overall force acting on a body when all individual forces have been considered
• if the net force is zero the forces are balanced and there is no state of motion

  if the net force is not zero the forces are unbalanced and there is a change in the state of motion
• what is limb Kinematics?

  • the study of motion in relation to time and space
  • a 3D image is created allowing joint and limb efficiency to be evaluated
  • this can be used for elite performers or patients requiring rehab
• what does limb kinematics measure?

  • bone gonimetry
  • displacement
  • velocity
  • acceleration
• how does limb kinematics work?

  reflective markers are placed on the joints of the performer which are used to capture the unique movements of the limbs during performance by multiple infa-red cameras
• what are the issues with limb kinematics?

  • accuracy depends on correct placement of body markers
  • results don't cater for individual differences
  • highly specialized technique, expensive, limited laboratories with them
• what are force plates?

  • data can be collected from an athlete placing their foot on the plate to analyze the pressure created on the plate
  • walking, running or jumping analysis can be carried out
• what do force plates measure?

  • gait analysis
  • balance
  • rehab and physical therapy
• how do force plates work?

  force transducers are included in the plate which is embedded in the ground - an electrical output is displayed in graphical form on the computer
• what are the issues with force plates?

  • specialist, expensive equipment mainly only available in laboratories
  • athletes may run/jump differently in a lab compared to in real sports situations
• what is a wind tunnel?

  analyze the amount of air resistance on object is creating whilst in motion
• what do wind tunnels measure?

  • aerodynamic efficiency
  • adjustments can be made to the designs to increase streamlining and therefore reduce the effects of air resistance
• how do wind tunnels work?

  • it can measure the forces produced by air against the surfaces of the object
  • e.g Maclaren has a 145m wind tunnel with a 4m wind turbine that can rotate up to 600rpm
  • technology such as Drag Reduction System (DRS) have been developed using wind tunnel technology
• what are the issues with wind tunnels?

  • very specialized facility
  • very expensive
• what are the vertical forces acting on a body?

  • weight
  • reaction
• what are the horizontal forces acting on a body?

  • friction
  • air resistance
• Vertical forces - Weight

  • the gravitational pull that the Earth exerts on the body
  • it acts downwards through the Centre of Mass
  • Weight (N) = Mass (kg) x Acceleration due to gravity (10 m/s/s)
• Vertical forces - Reaction

  • is the equal and opposite force exerted by a body in response to the action force placed upon it
  • relates to Newton's 3rd Law of Inertia
  • it works in opposition to weight
• if weight = reaction the body will remain at a constant height

  if weight < reaction the body will get higher

  if weight > reaction the body will get lower
• Horizontal forces - air resistance

  • is the force that opposes the motion through air
  • it works against a forward moving body
• what are the factors that affect air resistance?

  • velocity
  • shape
  • frontal cross-sectional area
  • smoothness of surface
• Horizontal force - Friction

  • force that opposes the motion of two forces in contact
  • friction acts forwards
• what are the factors that affect friction?

  • roughness of the ground surface
  • roughness of the contact surface
  • temperature
  • size of normal force
• if air resistance = friction speed will remain constant

  if air resistance < friction speed will increase

  if air resistance > friction speed will decrease
• what is the centre of mass?

  the point at which the body is balanced in all directions