Biomechanics Flashcards
Newton’s 1st law of motion (inertia)
an object in motion or at rest will stay in motion or at rest unless acted on by an external force
Newton’s 2nd law of motion (acceleration/momentum)
force = mass x acceleration (F=ma)
Newton’s 3rd law of motion (action/reaction)
For every action there will always be an equal and opposite reaction
Momentum formula
Momentum = mass x velocity
what does the principle of conservation of linear momentum state? when does it occur?
Principle states the total momentum of two objects before and after impact are equal, this occurs in situations where a perfect elastic collision takes place (no energy is lost to sound and heat)
Impulse, what does it refer to?
Impulse = force x time and refers to the change in momentum of an object
coefficient of restitution (COR)
The ratio of relative velocity (or height) after impact to the relative velocity (or height) before collision.
COR formula
COR = square root of (height bounced divided by height dropped)
concentric force
force applied to produce linear motion e.g. hitting a float serve in volleyball
Eccentric force
off centre force applied to produce angular motion e.g. hitting a top spin serve in volleyball
Types of forces
concentric force and eccentric force
force that creates angular momentum (torque)
Caused by the application of an eccentric (off-centre) force
Torque
The magnitude of the turning force
torque = Force x Distance (T = F x D)
Angular momentum formula
Angular momentum = angular velocity x moment of inertia
Angular velocity
the velocity or speed of a rotating object
Moment of inertia (mass of object x radius of rotation)
the resistance of a rotating object to change its state of motion
Conservation of angular momentum
A spinning body will continue spinning unless an external force acts on it
Levers main parts
Weight or resistance to be moved
axis or pivot point
application of force to move the weight or resistance
Lever functions
Increase application of force by making the force arm longer than the resistance arm
increase the speed of movement by making the force arm shorter than the resistance arm
Fulcrum/axis
point around which the lever rotates
effort/force arm
the distance between the fulcrum and the point at which the force is applied
Resistance arm
the distance between the fulcrum and the centre of the resistance
Input (effort) force
Force exerted on the lever
Output (resistance) force
Force exerted by the lever
First class lever
fulcrum is located in the middle of the effort and load
Second class lever
Load (resistance) in the middle of the fulcrum and effort
Third class lever
Effort (force) in the middle of the fulcrum and load
FLE lever acronym
FLE
- F - 1st class - Fulcrum in middle
- L - 2nd class - Load in middle
- E - 3rd class - Effort in middle
ARF lever acronym
- A - 1st class - Axis in middle
- R - 2nd class - Resistance in middle
- F - 3rd class - Force in middle
Factors affecting use of levers
- length of lever
- inertia of lever
- amount of force
Length of lever affect on lever use
velocity is greatest at the distal end of the lever
longer lever, greater velocity at impact
inertia of lever affect on lever use
longer lever = heavier lever meaning more difficult to rotate
amount of force affect on lever
determines the length of the lever athlete should use
fluid mechanics
the study of forces that develop when an object moves through a fluid medium (either water or air)
fluid resistance
as an object moves through a fluid the fluid becomes disturbed
the greater disturbance to the fluid, the greater the transfer of energy form object to fluid
2 factors affecting fluid resistance
density
viscosity
density
more dense fluid results in a more disturbed fluid therefore increasing the resistance e.g. humidity
viscosity
the more viscous the fluid (internal resistance of a fluid to flow), the more disturbed the fluid becomes therefore increasing resistance e.g. water is more viscous than air so a swimmer will experience more resistance than a runner
Types of drag
Form drag
surface drag
wave drag
form drag + factors affecting
the drag created due to a fluid moving over an object resulting in friction between the surface of the body and the fluid
- relative velocity of moving object
- relative roughness of surface object/surface friction
- viscosity of the fluid
- surface area of the object
form drag (pressure drag) + factors affecting
the drag created by a pressure difference between the front and rear of an object moving through a fluid
- cross sectional area (CSA) of the object presented to the fluid
- velocity of the object
- surface roughness (surface friction)
- shape of object
wave drag + factors affecting
the drag created by the body at the interface of two fluids interacting whereby waves are created
- relative velocity of wave
- technique
- open water (ocean) vs closed conditions (pool)
boundary layer
Thin layer of air surrounding or attached to the ball
Laminar
flow characterised by smooth parallel layer of fluid
Turbulent
flow characterised by mixing of adjacent fluid layers
boundary layer separation
where boundary layer breaks away from ball
earlier separation increases pressure gradient between the front and back of the ball, leading to increased drag
Turbulent flow characteristics
- high pressure at front of ball
- late boundary layer separation
- small turbulent pocket (high pressure) at rear of ball)
Laminar flow characteristics
- high pressure at front of ball
- early boundary layer separation
- large turbulent pocket (low pressure) at rear of ball
affecting factors of boundary layer separation point
velocity
- low velocity results in late separation and minor drag
- high velocity results in early separation and increased drag
surface roughness
- creates turbulent boundary layer, reducing effect of drag
- e.g. dimpled vs smooth golf ball
factors affecting drag
drag coefficient
cross sectional area
speed
surface roughness
mass
shape
Drag coefficient - factors affecting drag
- measurement used to quantify the drag or resistance of an object on a fluid environment
- directly related to cross sectional area
cross sectional area (CSA) - factors affecting drag
- linear relationship exists between CSA exposed to air and drag
- increased CSA = increased drag
Speed - factors affecting drag
- faster moving ball means earlier boundary layer separation, which means larger pressure differential between front and rear of ball therefore resulting in more drag
Surface roughness - factors affecting drag
- rough surface creates turbulent flow, therefore less drag
Mass - factors affecting drag
- greater mass of the ball means a less effect of drag
Shape - factors affecting drag
- round ball results in laminar flow oval ball results in turbulent flow
environmental factors affecting drag
air density
- higher altitude results in less drag
- smaller object leads to a greater drag effect
atmospheric pressure
- increased pressure = increased density = increased drag
humidity
- increased humidity = increased density = increased drag
temperature
- increased temperature = decreased density = decreased drag
Bernoulli’s principle
- the velocity of a fluid moving over an object is inversely proportional to the pressure on the object
- high velocity = low pressure
- low velocity = high pressure
Magnus effect
- Term used to describe the effect of rotation on an object’s path as it moves through a fluid
- It applies Bernoulli’s principle to explain the effect spin has on the trajectory or flight path of an object
biomechanical principles
balance
coordination continuum
force-motion
force-time
inertia
optimal projection
range of motion
segmental interaction
spin
coordination continuum - applies only to striking and throwing activities for distance
sequential approach to ensure maximum velocity transferred
- maximise number of body segments involved by standing side on
- sequentially accelerate each body segment
- ensure big body parts move first and small body parts move last e.g. arms to wrist
- follow through towards target to ensure safe dissipation of force
Balance
the ability of something to maintain or hold its position to increase stability
- widen base of support, increase surface area with ground, lower centre of gravity
force - motion
an objects motion is affected by the magnitude and direction of external forces acting on it
force - time (impulse)
- a product of the force applied to an object or body, and the duration it is applied for
range of motion (ROM)
the extent or limit to which a part of the body can be moved around a joint or a fixed point, total movement joint is capable of
Optimal projection
- maximise velocity
- maximise height of release
- angle of release (45 degrees)
Spin
Through the application of back spin to the ball, it optimises the balls time in flight (result of magnus effect), therefore maximising distance achieved.
