Biomechanics

• Linear motion - the change in position of an object in a straight line or in a single direction
• Speed - how fast an object is travelling, scalar quantity, size but not direction -> s=d/t
• Velocity - the speed in a particular direction, vector quantity. Calculated with: velocity = displacement/time taken
• Acceleration - rate of change in velocity, vector quantity, size and direction. Calculated with:

  Acceleration = (final velocity - initial velocity)/time taken - a=v-u/t

  Measured in m/s^2
• Angular motion - the motion of a body/mass about a fixed point to axis. The same principles in terms of velocity, displacement and acceleration used for linear motion apply to angular motion
• Moment of inertia - inertia is the amount of force required to move a mass in a straight line. Moment of inertia uses the same concept but relates to rotational movement. Therefore, the further away a mass is from the axis of rotation, the more 'spread out' the mass is. This would increase the moment of inertia and more force would be needed to move it.
• Angular momentum - product of angular velocity and moment of inertia. Angular momentum = MI x angular velocity. Therefore, if MI increases, velocity decreases and vice versa, providing there is no other force acting on the rotating object, then angular momentum is conserved.

  E.G. gymnast will tuck body in to decrease MI and increase angular velocity. As the gymnast looks to land, the limbs will move out from the axis of rotation, increasing MI and decreasing angular velocity to slow spin/rotations so they can land safely
• Projectile motion - refers to either an object or the human body as it travels through the air
• Forces acting on flight of a projectile: Gravity, air resistance, lift forces. If gravity was to present, a projectile would travel in a constant straight line. However gravity causes a projectile to track in a parabolic trajectory
• Parabolic flight - projectiles with a large weight and small resistance force follow a parabolic flight path, e.g. shot putt. Weight is dominant force
• Non-parabolic - where there is an increase in air resistance so the object falls more vertically, e.g. a shuttlecock is light and has feathers that catch air. Air resistance is the dominant force
• Angle of release - 45 degrees is optimal angle for release of a projectile. Lowe than 45 when release height is higher than landing height, javelin. 45 degrees when release and landing height the same, long jump. Higher than 45 when release height is lower than landing height, basketball shot.
• Factors affecting horizontal displacement:

  Height of release - the higher the release, the further the distance

  Velocity of release - higher release velocity will increase horizontal distance, seen in hammer throw
• Fluid mechanics - objects that move through the air or water. It involves the forces acting against moving objects within these mediums and how they slow them down
• Hydrodynamics - flow of water around a projectile which can influence the speed and direction of travel. Reduce drag by: streamline body position and flat in water, lean bodies, minimise turbulent flow by: tight fitting swimsuits, swimming hats, remove hair, maximise distance underwater at start of race. Shark suit is now banned - greatly reduced amount of drag
• Aerodynamics - flow of air around a projectile, influencing speed and direction of travel. Air resistance can be affected by: velocity - increase leads to increased air resistance, shape - the more aerodynamic the lower the resistance, cross sectional area - the smaller the area the lower the air resistance, smoothness of surface. The smooth the surface, the lower the air resistance. Cycling helmets - the more streamlined they are, leads to a decreased low pressure zone to reduce drag and increase speed. A golf ball is designed so air flow is close to the ball, decreasing wake
• Lift forces - interact with objects in flight and are caused by the aerodynamic shape of the object.
• Bernoulli principle - as velocity of a fluid increases, the pressure exerted by the fluid decreases. Since forces act from an area of high pressure to an area of low pressure, an uplift is created, providing high pressure is below the object or projectile. E.G. in discus, more lift is required during flight to maximise distance thrown. In this case, the angle of attack will be important as the discus will need to be tilted at the most appropriate angle. Pressure moves from high to low and as a result, a lift force is created and the discus stays in the air for longer
• Magnus effect - same as Bernoulli but with spinning objects.

  Top spin - increase in air resistance at the top of the ball, slowing the velocity and causing an area of high pressure. Below the ball, air is moving in the same direction as the spin, with an increase in velocity under lower pressure. High to low so ball drops.
• Side spin - can be applied when taking a free kick in football. Apply Magnus effect by curving the ball. High to low pressure dependent on the side it was kicked

  Back spin - increase in air resistance at bottom of the ball, slowing air flow leading to increase in pressure. Above the ball, air moves in the same direction as the spin, which increases velocity and decreases pressure. Ball stays in the air for longer