biomechanics yr 2 Flashcards
linear motion
movement of a body in a straight or curved line, where all parts move the same distance in the same direction over the same time
direct force
a force applied through the COM resulting in linear motion
5 linear motion descriptors
- distance
-displacement
-speed
-velocity
-acceleration / declaration
speed
the rate of change in distance
Angular motion
movement of a body or part of a body in a circular path about man axis of rotation
how does angular motion occur
from an eccentric force being applied to the body known as torque
longitudinal axis
runs from head to toe through the COM
e.g a flat spin of ice or full turn in trampolining
Transverse axis
runs from left to right through the COM.
e.g somersault
frontal axis
from front to back through the COM
e.g cartwheel
3 descriptors of angular motion
- angular velocity
-moment of inertia
-angular momentum
angular velocity
is the rate of change in angular displacement or simply the rate of rotation
angular displacement / time taken
measure in radians per second (rad/s)
moment of inertia
the resistance of a body to change its state of angular motion or rotation
sum of (mass x distribution of there mass from the axis of rotation2)
measured in kgm2
mass effect on moment of inertia
the greater the mass of the body the greater the moment of inertia
Hence, sports with high level of twists etc are performed by athletes with low mass as they can rotate easier and stop rotating with ease.
distribution of mass from the axis of rotation
the further the mass moves away from the axis of rotation the greater the moment of inertia and resistance to change state of motion
Hence, it is more beneficial to tuck around the axis of rotation as your moment of inertia will be lowered therefore you can rotate more quickly.
distribution of mass when running
recovery leg- mass is distributed close to the axis of rotation at the hip therefore moment of inertia is low and the leg moves back down quickly
drive leg- mass distributed further away from the axis of rotation therefore moment of inertia is higher and leg moves slowly
moment of inertia’s effect on angular velocity
if moment of inertia is high, resistance to rotation is high therefore angular velocity is low and the rate of the spin is slow
if moment of inertia is low resistance to rotation is low therefore angular velocity is high and spin rate is high
angular momentum
the quantity of angular motion possessed on a body
moment of inertia x angular velocity
angular analogue of newtons first law
’ a rotating body will continue to turn about an axis of rotation with constant angular momentum unless acted upon by an eccentric force or external torque’
fluid mechanics
the study of the forces acting on a body travelling through air or water
4 factors that affect levels of drag and AR
Velocity - the greater the velocity the greater drag and AR
Frontal CSA - larger the frontal CSA the larger the AR or drag.
Streamlining or shape - more streamlined for aerodynamic the shape of the body in motion the lower the Ar and drag
surface characteristics - the smoother the surface the reduced amount of Ar and drag there is
how do skiers minimise AR
smoothness of their lycra
minimise the FCSA by adopting a low couched position
wear tear dropped helmets to create streamlined shape
projectile motion
movement of a body through the air following a curved flight path under the force of gravity
projectile
a body that is launched into the air losing contact with the ground surface
4 factors that affect horizontal distance
speed of release
height of release
angle of release
aerodynamic factors
speed of release
links to newtons 2nd law as the greater force applied to the projectile the greater the change in momentum and therefore acceleration in the air
angle of release
45 degrees optimal angle
height of release
where release is above the landing height the optimal angle is less than 45 degrees e.g shot put and javelin
where release is below landing height the optimal angle is more than 45 degrees e.g bunker shot in golf
parabolic flight path
a flight path is symmetrical about its highest point caused by weight being the dominant force
non parabolic flight path
a flight path asymmetrical about its highest point as Ar is the dominant force
Bernoulli principle
higher the velocity of air flow the lower the surrounding pressure
lift force
additional force created by a pressure gradient forming on opposing surfaces of an aerofoil moving through a fluid
aerofoil shape impact on lift force
the curved upper surface forces air flow to travel a further distance and therefore move at a higher velocity
flat underneath surface allows air to flow a shorter distance therefore at a lower velocity
velocity increases pressure decreases
angle of attack
the most favourable angle of release for a projectile to optimise lift force
discuss is 17 degrees
Magnus effect
creation of an additional Magnus force on a spinning projectile which deviates from its flight path
Magnus force
a force created from a pressure gradient on opposing surfaces of a spinning body moving through the air
hook
a type of sidespin that is used to deviate a projectiles flight path to the left
slice
a type of sidespin that is used to deviate a projectiles flight path to the right
how Magnus force is created on a topspin shot
- upper surface of the projectile rotating towards the oncoming air flow ( top to bottom) decreasing the velocity of air flow - high pressure zone is created
- lower surface of the projectile rotating the same direction as there air flow increases velocity of air flow therefore a low pressure zone is created
-pressure gradient forming an additional Magnus force being created downwards means the ball ‘dips’ in flight and the flight path shortens
