Biomechanics Flashcards
1st law of motion
Every object will remain at rest unless acted upon by an external unbalanced force
2nd law of motion
Law of motion
rate of change of acceleration to a body is proportional to the force applied to it and inversely proportional to the mass of the objects.
Greater force = greater acceleration
less mass = greater acceleration
f=ma
Momentum
measure of the amount of motion possessed by a moving body and can be expressed mathematically as p=mv (mass x velocity)
More momentum = more force to stop object
conservation of linear motion
Principle states the total momentum of two objects before and after impact are equal.
Perfectly elastic collision - the momentum of one object is transferred on contact to the other object, resulting in no change in total momentum, rather than a transfer of momentum.
Inelastic collision - all momentum lost (eg. Hacky sack falling on ground)
Impulse
The application of force over a period of time to change the momentum of an object.
impulse = time x force
The longer a force can be applied, and the greater the force that is applied, the greater the object’s impulse or change of momentum.
change of momentum
3rd law of motion
For every action, there is an equal and opposite reaction
when two objects exert a force upon each other, the forces are opposite in direction and equal in magnitude
Law directly applies to the concept of conservation of momentum.
explains that when collisions occur, an equal and opposite force occurs resulting in a transfer of momentum from one object to the other.
Coefficient of restitution
measure the elasticity of the collision between an object and a given surface.
It measures how much energy remains in the object after a collision takes place
Measured on a scale of 0-1 - 0, perfectly inelastic, all energy lost. 1, perfectly elastic, all energy kept.
Formula of coefficient of restitution
COR = square root of height bounced/height dropped
factors of COR
temp of the balls: increase temp - increase COR
Velocity of the ball: increased velocity increases likelihood of ball losing energy due to greater compression of the ball - decreases COR
Equipment and materials: condition of equipment eg.ball, type of equipment, type and condition of playing surface.
elasticity
Measure of how much rebound exists following a collision
concentric force
Force applied to produce linear motion
(eg. Slapshot) - puck moves straight, hit in the middle.
Eccentric force
off centre force applied to produce angular motion
(Hitting a top spin serve in volleyball)
Force couples
When two equal, but oppositely directed forces act on opposite sides of an axis of rotation
this causes the forces that produce linear motion to cancel each other out, causing the object to rotate in a fixed position.
Angular momentum
quantity of angular motion possessed by a rotating body and is expressed mathematically as:
Angular momentum = angular velocity x moment of inertia
moment of inertia
Refers to resistance of a rotating object to change its state of motion
if mass of an object is distributed close to the axis of rotation, the MOI is small and it is easier to rotate object.
As mass of an object moves further away from the axis of rotation, the MOI increases and rotation becomes harder
increase MOI - harder rotation
Moment of inertia = mass of object x radius of rotation
Longer moment arm (mass from axis of rotation) = increase moment of inertia, object harder to control and harder to generate angular velocity.
conservation of angular motion
Increased MOI = decreased AV
increased AV = decreased MOI
torque
The turning effect created as a result of an eccentric force being applied around a pivot or axis
torque = force x distance (perpendicular distance)
Distance between where the force is applied and where the torque is produced - moment arm
levers
To increase or magnify the force applied
1st class lever - resistance arm, axis, effort arm
2nd class lever - axis, resistance arm, effort arm
3rd class lever - axis, effort arm, resistance arm
Lift forces
refers to the component of force that acts perpendicular to the direction of flow, will act at a right angle to the direction of motion. Can act in upwards and downwards direction.
Only occurs in objects which are spinning or no perfectly symmetrical.
lift is created by different pressures on opposite side of an object due to fluid flow past the objects.
Bernouilli’s principle
States that as the velocity of a fluid increases, the pressure the fluid exerts on an object decreases.
the velocity is inversely proportional to pressure.
Magnus effect
Term used to describe the effect of rotation on an object’s path as it moves through a fluid.
it applies Bernouilli’s principle to explain the effect spin has on the trajectory or flight path of an object.
Spin
when a ball is struck with an eccentric force, there is both linear and angular rotation.
Rotating ball interacts with the oncoming air
the resultant movement - curve
Fluid flow
the natural science of fluids in motion
Fluid resistance = lift x drag
as an object moves through a fluid, it disturbs it.
The greater the disturbance to the fluid, the greater the transfer of energy from object to fluid
factors affecting fluid resistance
Viscosity (fluid) - the more viscous the fluid, the more disturbed the fluid becomes and hence the greater the resistance
Density (air) - the more dense the fluid, the more disturbed the fluid becomes and hence the greater the resistance.
Types of drag
surface drag
Form drag
wave drag
Surface drag
friction produced between fluid and surface of a moving object
Factors affecting: relative velocity of moving object (H v = H SD), relative roughness of the surface (H R = H SD), viscosity of the fluid (H Vi = H SD), surface area of the object (H SA = H SD)
H = high, L = low
Form drag
resistance created by pressure differential between front and back of an object moving through a fluid.
Factors affecting: cross sectional area (CSA) of the object presented to the fluid (H CSA = H FD), Velocity of an object (H V = H FD), surface roughness (H Sr = L FD)(rougher surfaces cause the air to cling to the surface for longer period, causing a later separation point and hence less drag), shape of object (eg. round vs oval)
Wave drag
Resistance formed by creation of waves at the point where air and water interact.
seen as the major form of drag acting on a swimmer.
Factors affecting: relative velocity of the wave (H V = H WD), technique - being streamlined in the water, swimmers can reduce effect of wave drag, open water (ocean vs closed conditions (pool).
boundary layer
Boundary layer separation: where boundary layer breaks away from object.
the earlier the boundary layer separation, the greater the pressure gradient between the front and back of the ball. (Leads to increased drag)
Laminar vs turbulent flow
laminar flow - a type of fluid in which fluid moves smoothly in individual layers or streams, each layer parallel to each other
Turbulent flow - flow in which the velocity at any point varies erratically, layers flow independently and randomly (not parallel)
factors affecting boundary layer separation
Velocity: low - boundary layer clings to surface, separation well towards near. High - separation occurs further forward.
surface roughness: rough - creates turbulent boundary layer, reducing effect of drag.
Sequential movement
use a large number of body segments from legs through core and upper body and limbs.
Use larger slower moving body parts first then smaller faster moving body segments.
initiates by getting balanced, with widen base of support to gain a stable base of support, this allows for optimal transfer of momentum between body parts.
Each segment begins once the previous segment has reached peak velocity.
follow through to prevent deceleration
All forces are directed towards the target.
balance
Ability to remain stable or steady or upright.
gained by achieving an even equilibrium/distribution of forces (weight) around the base of support.
Ensure you have a large stable base to ensure all segments rotate around a stable base.
line of gravity remains above base of support.
Maximise points of contact wt the ground
lower centre of gravity
Range of motion
refers to the extent of a motion around a joint
Optimal projection
when angle, velocity and height of release combine to meet the demands of the task
