Biomechanics Flashcards
On a diagram/graph showing the flight path of an object, what force changes size and which doesn’t?
Vertical force changes size and goes from +ive to -ive.
Horizontal force remains constant (ignoring air resistance)
what is the optimum angle of release?
45 degrees
Define the Bernoulli Principle
Refers to changes in fluid pressure (H20 or air) due to diff. in fluid velocity
What does fluid flow around irregular shaped projectiles cause? Why?
Pressure differences
== Molecules have to travel diff. distances to pass around it.
What shaped objects produce lift?
Aerofoil (wing shaped)
Describe how air flows over aerofoil objects
Air travels a longer distance on top = low pressure = high velocity
Air travels shorter distance underneath = high pressure = low velocity
What does fluid moving at high + low speed cause?
High speed = drop in pressure
Low speed = increase in pressure.
What happens with the slower moving fluid + the faster moving fluid?
Slower moving will exert higher pressure on object than faster fluid === lift or downforce.
Give an example of a lift in an object
Air moves quickly over the top of a discus that is released at an angle == so its lifted.
What happens to a ski jumper in Bernoulli’s principle
Will attempt to adopt an aerofoil position to maximise lift as curve on top + flat underneath
How are formula 1 cars designed to counteract the Bernoulli effect
Using ‘upside down’ aerofoils (spoilers) to ⬆️ fluid pressure above car, pushing it down onto track.
What is the Magnus effect
Bernoulli Principle applied to spinning objects.
Spin is created by applying a force outside an object’s centre of mass.
What does spin cause the projectile to do?
Curve away from it’s original flight path.
The side spinning in the direction of the air will result in a high velocity = low pressure causing a pressure differential.
How is top spin created?
By applying a force ABOVE centre of mass.
i.e hitting tennis ball low to high + brushing over ball == forward rotation around transverse axis.
What does top spin result in?
Causes a Magnus force to act on the ball in a downwards direction.
== Tennis players can then hit the ball harder but still ensure it lands in-court.
Why do top spin strokes tend to be harder to return?
Magnus effect results in a higher bounce.
How is back spin created?
By applying a force BELOW centre of mass.
i.e hitting a tennis ball high to low + slicing under ball == backward rotation around transverse axis.
What does back spin result in?
Causes a Magnus force to act on ball in an upward direction.
Define angular motion
Movement around a fixed point or axis.
Occurs when a force is applied OUTSIDE the centre of mass.
Define angular displacement
Smallest change in angle between starting + finishing point, how far something has turned. (Radians)
i.e in 1 pirouette = angular displacement: 0 rads.
Define angular velocity
Rate of change of angular displacement, how quickly something spins.
(rad/s)
Define angular acceleration
Rate of change of angular velocity, how quickly somethings gets spinning or slows spinning.
(rad/s^2).
Define moment of inertia
The resistance of a body to angular motion
kg/m^2
What does the moment of inertia depend on
Mass of body
Distribution of mass around the axis - radius of gyration.
How must an athlete increase angular velocity?
By bringing their mass TOWARDS the axis of rotation by changing the shape of their body, tucking in.
What remains conserved in the graphical representation of a somersault?
Angular momentum
Whilst moment of inertia + angular velocity are inversely proportional to each other.
What can fluid be a representation of in fluid mechanics?
Air or H20
Define laminar flow
When fluid layers move parallel to each other + don’t cross.
a.k.a streamlined flow
Define turbulent flow
Irregular + rough.
Characterised by small ‘whirlpool’ regions in the fluid layers.
What happens to the fluid nearest an object when the object moves through it?
Slows down.
Mol. of fluid near object (boundary layer) are disturbed + move around.
What is the behaviour of the fluid around the object dependent on?
Shape (front cross-section + surface)
Speed
Viscosity
What is drag force
An ⬆️ in fluid resistance = resisting motion
How can performers overcome drag forces?
⬇️ cross-sectional area (i.e tucking in)
Manipulate surface properties (i.e swim caps + compression clothing)
Consider ⬆️ speed vs drag
What is the relationship between speed + drag?
Faster the object = greater the drag.
How might a swimmer minimise turbulent flow
By analysing laminar flow + attempting to alter boundary layers
How might an athlete decrease or increase surface friction?
By choice of footwear.
How might cricketers attempt to ⬆️ turbulent flow
By creating more boundary layers to generate swing.
Rough surface on 1 side = asymmetrical flow/wake + ball moves in direction of turbulent flow.
How are golf balls designed to take adv. of turbulent flow
Dimples create turbulence which sucks air to ball to delay separation.
In which a smaller vortex creates less drag.
Explain, using the Bernoulli principle, how the lift force is generated
Air flows faster over top of discuss as it has further to travel = low pressure created.
Air flows at a slower velocity under discuss as it has shorter distance to travel = high pressure created.
=== Pressure gradient
As air moves from area of high to low pressure, lift force is generated.
Object needs to be an AEROFOIL SHAPE
