Fluid Dynamics 26-28 Flashcards
what is a fluid?
fluid is any substance that tends to flow or continuously deform when acted on by a shear force.
viscoisity
the internal resistance of a fluid to flow. fluids more dense are more viscous.
buoyancy
fluid force acting upward is equal to the wieght of the fluid displaced by the body.
archemedes principle
physical law stating that the buoyant force acting on a body is equal to the weight of the fluid displaced by the body
volume or mass ?
less to do with mass and more the shape of the object on whteher it will sink or flaot.
densiometry equation
body density = Wdp / ((Wdp - Wsp)/ Pw - RV)
do our buoyant forces act throught the same place as the CoV and CoM.
our buoyant forces run through the same place as our centre of volume but this might not be the same as centre of mass (CoG)
will people with greater body volume float easier?
greater body volume = larger buoyancy forces.
will people with fat or muscle have harder time floating
people with higher muscel mass will find it harder to float as it is more dense than fat.
three types of drag
surface/viscous, form and wave.
what is the coefficient of drag
an index of a body’s ability to generate fluid resistance.
what is surface/viscous drag
ski/surface friction is derived from the sliding contacts between successive layers of fluid close to the surface of a moving body. based on the amount of surface area pushing through the air.
what is the boundary layer
layer of fluid imeediatly adjacent iwith the moving object.
form drag
resistance created by a pressure differential between the lead and the rear sides of a body moving through a fluid.
how does form drag create spin
when a ball is spinning the side spinning with the air will ahve low pressure whereas the side spinnig against the air will ahve high pressure make it go the way the way of the low pressure.
contributors to drag force
shape, speed and surface roughness
what is the negative pocket in form drag?
the area of low pressure behind a moving object. i.e. drafting in biking.
wave drag
resistance created by the generation of waves at the interface between two different fluids, such as air and water.
lift force
this is a force generated perpendicular to the fluid flow.
bernoulli principle
regions of relatively high-velocity fluid flow are associated with regions of low pressure and the regions of low velocity are associated with regions of relative high pressure.
magnus force
lift created by spin.
what does a foil shape do for the bernoulli principle
creates fluid separation with the high velocity - low pressure over the top and lower velocity - higher pressure over the bottom.
angle of attack with lift force
the angle of orientation of the projectile with respect to the fluid flow.
what is the optimum angle of attack for maxmising range?
the angle at which the lift/drag ratio is maximum.
other ways to create swing
add seamd and add polish.
what happens in a coventional swing
the bowler will have the seam facing the way the want the ball to go. the seam will create turbelent flow which is low pressure and the ball will follow this direction.
revsere swing in cricket
seam is angled to the right or left but the rough side is also facing the same way. if the ball is bowled fast enough (85mph) the laminar layer goes into a turbulent state before reaching the seam. making the ball go the opposite way to the seam.
what could possible ball tampering be in cricket
making the rough side rougher or picking at the seams.
