Biomechanics P1 Flashcards
Horizontal forces
Friction and Air resistance
Velocity
Velocity = displacement /time
Momentum
Momentum (Kg M/s) = Mass x Velocity
Acceleration
Acceleration (m/s2) = (final velocity-initial velocity)/time taken
Weight
Weight (N) = Mass x Acceleration due to gravity
Force
Force (N) = Mass X Acceleration
Air resistance
the force which opposes motion through the air
Friction
the force that oppose the motion of two surfaces in contact
Reaction
Equal and Opposite reaction force exerted by a body in response to the action force placed upon it
Weight definition
the gravitational pull that the earth exerts on a body
Measured in newtons
Unbalanced force
when two forces are unequal in size and opposite in direction
Balanced force
When two or more forces acting on a body are equal in size and opposite in direction
Net force
Sum of all the forces
Newtons third law
Law of Reaction
-A force that is applied to an object will react with equal and opposite force.
‘to every action there is an equal and opposite reaction’
e.g. a forward and upwards action is place upon a football from the foot, the ball will apply an equal and opposite down and backwards reaction force to the players foot.
Newtons second law of motion
Law of Acceleration
Momentum is the amount of motion possessed by a body. This acceleration is proportional to the force place upon it.
‘The rate of change of momentum in a body is proportional to the force applied and change that takes place in the direction in which the force acts’
Force = Mass X Acceleration
E.g. The larger the size of force applied to the rugby ball, the greater the rate of change in momentum and acceleration towards the post. The ball will accelerate in the same direction as the force applied towards the post.
Newtons 1st law of motion
-Law of Inertia
-A body has gravity that pulls the mass down towards the ground
The greater the mass the greater the inertia to change its state
‘A Body will continue in its state of rest or motion in a straight line, unless external forces are exerted upon it’
- E.g. a sprinter in the blocks will rest there, the larger their mass the larger amount of inertia they will need to accelerate out of the blocks.
Centre of Mass - definition
is the point at which a body is balanced in all directions
Stability - definition
the ability of a body to resist motion & remain at rest
or for a body to withstand a force applied & return to its original position without damage
Levers - definition
Lever systems are the co-ordination of our bones and muscles
-create human movement
Centre of MASS - Desription
COM is the point at which a body is balanced in all directions.
Athlete in anatomical position, com = naval
location depends on distribution of body mass - manipulate to improve sporting technique → alter body shape
COM 2
the com can move outside body
acts as point of rotation
the com of a football is the centre
if an athlete raises arm, com raises
If bend knees, com lowers
High Jump - Fosbury flop
- Mexico city Olympics 1968
- Gets the COM to travel underneath the bar
- Use a J-Curve to allow greater velocity in the approach
- Plants outside foot to allow inside leg to lift with arms to take off, COM is high
- Fully extend spine to rotate around the bar moving the COM outside the body + below the bar
Stability - factors affecting COM
- Mass of Body - greater the mass, greater the inertia to move out of state of rest e.g. sumo wrestlers
- Height of COM - lower COM = greater stability, Higher COM = less stability e.g. landing a tuck jump, bend at knees to lower COM
- Base of support - the greater the size of the base of support, the greater the stability. Small base = less stable e.g. two hands & feet down in bridge position
- Line of gravity - imaginary line which extends from COM downwards to floor, the more central the LOG to Base the greater the stability
Lever systems
functions: generate muscular effort to overcome a given load, increase the speed of a given movement
Components:
- Lever - bone, rotate around a fixed point
- Fulcrum - joint, the fixed point in the human body
- Effort - muscular force, when muscle contracts an effort is created
- Load - weight or resistance, object or mass of body
e.g. Upward phase of bicep curl, the biceps brachii creates the effort, the fulcrum = elbow and load is weight of forearm (3rd class)
Lever classifications
1st class, e.g. a header in football, Fulcrum in middle of the effort and load (EFL)
2nd class, e.g. ball of foot in take of phase of high jump, Load in the middle of F +E (ELF)
3rd class, e.g. flexion of elbow during a bicep curl, Effort in the middle of L+F (FEL)
Mechanical advantage
2nd class lever systems
MA= Effort arm/ Load arm
Effort arm is greater than Load arm
Large load moved with small effort
Mechanical disadvantage
3rd class
Load arm is greater than effort arm
A large effort is required to move a small load
Load Arm
the distance from the load to the fulcrum
Effort Arm
the distance from the fulcrum to the effort
Reliability
the extent to which an experiment gives the same results after repeated trials
Validity
How well a test measures what it claims to measure
Limb Kinematics
- Study of movement in relation to time and space
- allows joint & limb efficiency to be evaluated with measuring bone geometry, displacement, velocity and movement.
- Motion analysis records an athlete performing a action, linked to computer software which converts motion into digital format
- use reflective markers to detect the joint/limb
Limb Kinematics - Evaluate
+ data is immediate, objective, highly accurate
-highly specialised, expensive and limited to laboratory conditions - some actions = difficult
Force plates
- measures ground reaction forces in labs
- Metal rectangular plate w build in force transducers sunk into the ground
object makes contact = an electrical output proportional to force applied is displayed in a graph
Collect data through athlete running, jumping on the force plate
Asses the size and directions of forces
force plates evaluation
+creates immediate, accurate & reliable results - easy to analyse & apply to performance
-specialist, expensive and housed in laboratory conditions
Wind tunnels
object is placed inside with instruments to measure the forces produced by the air against the surface
- aim is to improve the flow of air around an object, streamlining the object
- F1 teams spend millions getting the aerodynamics of a car right, McLaren have their 145m long wind tunnel for testing aerodynamic parts & set-up → reduces drag reduction by reducing the rear flap angle by 4 degrees → decreases air resistance up to 7% →improved chances of overtaking
Wind tunnels evaluate
+allow engineers to tightly control environmental variables like wind speeds or wind direction →can control cross winds & measure air resistance & flow with precision accuracy
-specialised facilities, housed in engineering bases, expensive and require complex analysis of the results of the research professionals
Linear Motion
motion in a straight of curved line, with all body parts moving in the same distance at the same speed in the same direction
occurs when a force acts upon the COM of an object
Distance
length of the path the body follows when moving to a point
metres
scalar
displacement
length of a straight line joining the start and finish points
metres
vector
Displacement = velocity x time
speed
the rate of change of position
scalar
Metres/second
Speed = Distance/Time
velocity
the rate of change of position with reference to direction
vector
velocity = displacement/time
acceleration
rate of change of velocity
occurs when velocity increases, deceleration occurs when velocity decreases
vector
Metres/Second squared
A= final velocity - initial velocity/time
Linear motion graphs
Angular analogue of Newton’s Law 1
an object remains at rest or at a constant angular velocity about it’s axis unless acted upon by an external torque
e.g. Ice skater performs a pirouette an applies an external torque to slow down
Angular analogue of Newton’s 2nd law - law of acceleration
-the rate of change of angular momentum is proportional to the torque applied in that direction
angular analogue of newtons 3rd law - law of reaction
to every torque there is an equal & opposite torque
a torque is an eccentric force at distance from the axis
Moment of inertia
Inertia is resistance to change in a linear motion
Moment of inertia is the resistance of a body to angular motion
2 factors: Mass of body, the greater the mass the greater the resistance to change therefore the greater the MOI & Distribution of mass from the axis of rotation, the closer the mass is to the axis of rotation, the easier it is to turn - MOI is low
ex. gymnasts have an advantage as they have a smaller distribution of mass → low MOI & high angular velocity
Moment of inertia formula
MOI (kgm2) = mass (kg) x distribution of mass from the axis (m2)
angular velocity
angular velocity is inversely proportional to moment of intertia
angular motion
movement around a fixed point or axis
occurs when a force is applied outside the COM, a torque
torque
a rotational force causes an object to
turn about its axis of rotation
Axis of rotation
-Longitudinal: runs from top to bottom through top of head e.g. pirouette
-Frontal: runs from front to back through navel e.g. cartwheel
-Transverse: runs from left side to right side across the body e.g. Forward roll
Planes
- Transverse: divides body into upper and lower. Allows for rotation, supination & pronation e.g. golf swings
- Sagittal: divides body into left and right. Allows for flexion & extension. e.g. squatting
-Frontal: divides body into front and back. Allows for adduction, abduction and lateral flexion. e.g. star jumps
anagram from planes & axis of rotation
FIRST ARE FAT PPL (frontal & frontal)
THEN ARE SKINNY PPL (transverse & sagittal)
LAST ARE TALL PPL (Longitudinal & transverse)
angular momentum
angular momentum is spin, it involves an object or body in motion around an axis
depends upon the MOI & angular velocity
if MOI increase, AV decreases - inversely proportional
AM (kgM2 rad/s) = MOI (kgm2) x angular velocity (rad/s)
conservation of angular momentum
AM is conserved unless an external torque acts upon it
e.g. at take off a diver creates AM from an eccentric force arounds transverse axis, straight boy position = MOI is high & AV is low, rotation is slow
in a tucked body position the distributed mass is close together, MOI is decreased & AV increases causing a faster spin
fluid mechanics
the study of forces acting on an object through the air/water
E.g. Air resistance - air, Drag - water
Air resistance
a force that opposes the motion of a body travelling through the air
Drag
is a force that opposes the motion of a body travelling through water
depends on the environment
Aerofoil
streamlined shape w a curved upper surface & flat lower surface, giving an additional lift force to a body
Factor impacting the magnitude of Fluid mechanics
- Velocity - the greater the velocity, the greater the air resistance/drag, square the velocity & Fluid mechanics quadruples. e.g. Track cycling, speed skating, freestyle swimming
- Frontal cross-sectional area - the smaller the area = the smaller the AR/Drag, same with large. e.g. Track cycling & downhill skating
- streamlining - the more streamlined & aerodynamic the shape of the body in motion, the lower the AR/drag
- shape - more aerodynamic = lower fluid mechanics
- surface characteristics - the smoother the surface, the lower the AR/ drag. e.g. Swimming - wear race suits to create the smoothest surface to reduce friction.
Streamlining
the creation of a smooth air flow around an aerodynamic shape
Examples of Reducing AR/Drag in formula 1
- Low position of car reduces drag
- channelling of air as it has vents to break the opposing motion
- Front-wing creates downwards force
- Side channels, divert the air
- Smooth surface
- Curved upper surface & flat lower surface as a lift force
Examples of reducing ar/drag in cycling
- Low crouched position, gives a low frontal cross sectional area
- wear a tear dropped shaped helmet to streamline
- bike has a solid wheel to reduce air resistance
- wear lycra suits to create a smooth surface therefore reducing friction between the body surface and the air
projectile motion
the movement of a body through the air following a curved trajectory under the force of gravity
in flight the forces acting are weight which pushes downwards and air resistance, which acts opposing to the direction of travel
Factors affecting flight path
-speed of release, the greater the speed of the projectile, the greater the horizontal distance travelled, links to newton’s 2nd LOM, Acceleration = force applied
-height of release, if the height of release is greater than landing height, the optimum angle of release is less than 45 degrees, if hor is less than landing height = 45 degrees, travels furthest
-angle of release, greater than 45 degrees the projectile will reach its peak too quickly, lower than 45 degrees the object thrown will not achieve sufficient height
-Lift factors
Parabola
is a symmetric trajectory
occurs when weight is the dominant force as it acts vertically down as air resistance opposes a body travelling through the air
e.g. a shuttlecock hit gently follows a parabolic trajectory, if hit hard = a symmetrical trajectory as at high speed the force of AR is greater than the Weight
free body diagrams
should be big
a snapshot of forces acting on the object at 3 phases of motion during flight
a projectile with a large weight & small air resistance will follow a perfect parabolic flight path
if weight is dominant = parabolic flight path
if AR is dominant = non parabolic flight path
R is resultant force, shown by a parallelogram
non parabolic flight path
if weight is dominant = parabolic flight path
if AR is dominant = non parabolic flight path
R is resultant force, shown by a parallelogram.
In diagram, AR acts against the forward motion & loses momentum, then falls vertically downwards due to gravity
Bernoulli’s principle
states that the higher the velocity of air flow the lower the surrounding pressure
Bernoulli discovered that with an aerofoil shape travelling at a velocity, it splits air layers - top travels further over curved upper surface, travels faster creating a low pressure zone
The bottom layer impacts the aerofoil creating an area of high pressure, this pressure gradient creates LIFT
LIFT enables projectiles such as ski jumping to travel further & have more time in the air
Ski Jumping - using Bernoulli’s principle
- smooth surface charachteristics, using a wired suit to catch the wind to decrease air resistance
- aerodynamic helmets & goggles to reduce drag
- Body position creates large surface area
- Long wide ski’s create LIFT
- Angle of attack of 17 degrees
The magnus effect def
creation of an additional magnus force on a spinning projectile which deviates from the flight path
magnus force def
a force created from a pressure gradient on opposing surfaces of a spinning body through the air
Hook def
sidespin
used to deviate a projectile’s flight path to the left
Slice def
sidespin
used to deviate a projectile’s flight path to the right
spin
create by applying an external force outside the centre of mass, where the eccentric force is applied will determine the way the projectile spins
Topspin
eccentric force applied above the centre of mass
=> spins downwards (downwards magnus force) towards transverse axis
shortens flight path
Back spin
eccentric force applied below the centre of mass
spins upwards around the transverse axis
creates upwards magnus force, lengthening path
Sidespin hook
eccentric force applied right to the centre of mass
spins left around longitudinal axis
creates a magnus force to left swerving projectile left
Sidespin slice
eccentric force applied to the left of the centre of mass
spins right around the longitudinal axis
creates magnus force to right, swerving projectile to the right
spin used in tennis/table tennis
placing spin on the ball gives stability in flight, guides air flow and reduces turbulence.
topspin shortens the flight path meaning that the player can hit a ball harder ensuring it will still land in court/on table. E.g. a topspin serve will in tennis. It can also confuse the opposition, bringing them closer to the net & unexpectedly putting them in defence position.
explanation of topspin
the upper surface of the projectile rotating towards the oncoming air flow which opposes motion, decreasing the velocity of air flow - high pressure zone is created
the lower surface of the projectile rotating in the same direction as the air flow, increases the velocity of air flow & creates zone of low pressure
pressure gradient forms & an additional magnus force being created downwards
add weight to projectile & effect of gravity is increased
projectile ‘dips’ in flight giving less time in the air as the flight path shortens
the upper surface of the projectile rotating towards the oncoming air flow which opposes motion, decreasing the velocity of air flow - high pressure zone is created
the lower surface of the projectile rotating in the same direction as the air flow, increases the velocity of air flow & creates zone of low pressure
pressure gradient forms & an additional magnus force being created downwards
add weight to projectile & effect of gravity is increased
projectile ‘dips’ in flight giving less time in the air as the flight path shortens
Backspin explained
the lower surface of the projectile collides with oncoming air molecules, speeding up the air & creating low pressure
the top surface decelerates the air the top layer creating a high pressure.
the pressure difference creates lift - magnus effect
this left allows the ball to spring back up and have a longer flight path with more power.
sidespin hook explained
air flow opposes motion of the ball
Ball rotates to the left, guiding air flow
ball rotates against air flow on right side resisting air flow
pressure gradient is formed
magnus forces acts to deviate the flight path to the right
sidespin slice explained
Air flow opposes motion
ball rotates to the right, guiding air flow and creating low pressure
ball rotates against air flow on left side, resisting air flow and creating high pressure
pressure gradient formed
magnus force acts to deviate the flight path to the right
