Biomechanics

• linear motion is movement of a body in a straight or curved line, in the same direction, time and speed
• when does linear motion occur?


  a direct force through the centre of mass
• 6 quantities of linear motion are distance, displacement, speed, velocity, acceleration and deceleration
• equation for acceleration and deceleration is?

  final velocity-initial velocity divided by time taken
• velocity is rate of change in displacement measured in m/s
• acceleration is rate of change in velocity measured in m/s/s
• displacement is shortest straight line route from start to finish
• angular motion is movement of a body in a circular path around an axis of rotation
• when does angular motion occur?

  an eccentric force outside the centre of mass
• the 3 axis of rotation are longitudinal, transverse and frontal axis'
• what is angular motion measured in?


  radians
• angular distance is the total angle a a body turns from start to finish around an axis
• what is angular speed and velocity measured in?

  rad/s
• moment of inertia is resistance of a body to change its state of angular motion, measured in kgm squared
• angular momentum is the quantity of angular motion possessed by a body measured in kgm squared times rad/s
• 2 factors affecting size of moment of inertia are?

  mass and distribution of mass from axis of rotation
• if moment of inertia is high, resistance to rotation is high meaning angular velocity is low and therefore rate of spin is low
• if moment of inertia is low the resistance to rotation is low meaning angular velocity is high and therefore rate of spin is high
• angular momentum and newtons first law are in close relation to each other.
• angular momentum is a conserved quantity as it remains constant until an external eccentric force is applied
• 4 factors affecting magnitude of air resistance and drag on a body?

  velocity

  frontal cross sectional area

  streamlining and shape

  surface characteristics
• the greater the velocity the greater the air resistance and drag
• the larger the frontal cross sectional are the greater the air resistance and drag. can be manipulated by reducing the size of cross sectional area
• the more streamlined the shape of a body the lower the air resistance and drag, for example aerofoil shape
• the smoother the surface the lower the air resistance and drag will be. can be manipulated by wearing smooth clothing
• 4 factors affecting horizontal distance travelled by a projectile?

  speed of release

  height of release

  angle of release

  aerodynamic factors
• optimal angle of release is 45 degrees, if its above 45 degrees projectile will peak too early and rapidly return to the ground
• 45 degrees is only the optimal height of release if release height and landing height are equal, for example a shot put release height is higher than landing height
• speed of release is in direct correlation with Newton's Second Law
• Newton's second law in terms of speed of release is the greater the force applied to the projectile the greater change in momentum and therefore acceleration to projectile
• a parabolic flight path occurs if the weight is the dominant force and air resistance is very small, for example a shot put. it will follow a symmetrical flight path about its highest point
• a non parabolic flight path will occur if air resistance is the dominant force and weight is very small, for example a badminton shuttle. it will follow a asymmetrical flight path about its highest point
• free body diagrams show the weight and air resistance acting on a body during flight
• parallelogram of forces considers all forces acting on a projectile in flight
• if resultant force is closer to weight arrow, weight is the dominant force and it follows a parabolic flight path. opposite if resultant force is closer to the air resistance
• Bernoulli's principle explains an additional lift force can be created during flight based on shape of a projectile
• for example a ski jumper gets into an aerofoil shape, which means they lower surface is flat and upper surface is curved.

  flat lower surface = shorter distance to travel = slow velocity = high pressure

  curved upper surface = further distance to travel = fast velocity = low pressure

  fluids move from areas of high pressure to low pressure which generates the additional lift force
• angle of attack is the most favourable angle to release a projectile to optimise lift force, for example discus angle of attack is 17 degrees
• downward lift force can also be created by an inverted aerofoil shape
• f1 cars create low velocity on top as the surface is flat meaning less distance to travel = high pressure zone (rear wing also has inverted aerofoil shape forcing air underneath).

  bottom of car is high velocity due to distance of travel = low pressure zone (front wing has gaps to force more air down

  high to low pressure adds the additional downward force