what is the buoyancy force
- acts in opp direction of gravity
- dependent on relationship btwn density and volume
- always acts vertically upward in GRS
based on buotancy when will an object sink/be motionless/float
sink: in water when specific gravity is >1
- until wieght of displaced water equals weight of object (will never happen so will settle)
motionless: weight of displaced water equals weight of object
float: in water when specific gravity <1
what is relative velocity?
difference btwn the velocities of the two systems
how do you find relative velocity during a head wind
add the velocities together
- or subtract the negative b/c the velocity will be going in opp direction of you
- fluid going opp direction than object
how do you find relative velocity during a tail wind?
subtract velocities
-fluids going in same direction as object
how do you find relative velocity during a perpendicular cross wind
cross wind does not effect velocity of the system
how do you find relative velocity during an angled cross wind
- only look at x comp of velocity of wind
- identify if it is a tail or head wind then add or subtract x comp (tail: subtract, head: add)
laminar vs turbulent flow
lam: fluid flows smoothly around object and streamlines remain intact
turb: non smoothly flowing fluid and streamlines are broken
what is drag force
equation for drag
- force that acts parallel and in opp direction of object moving
- =(1/2)(CD)(CSA)(FD)(V2)
break down the equation for drag
- CD: coeffcient of drag; reflects streamlinedness of objects
- CSA: cross sectional area, surface area in contact w/ fluid flow, perp and para CSA
- FD: fluid density, increase = increase in drag
- V: relative velocity, dominant factor in drag force
factors affecting surface drag
4 of them
- smoothness of object
- parallel CSA of object (sides)
- density of fluid
- relative velocity
factors affecting form drag
4 of them
- shape of object msotly the change of shape toward trailing edge
- perpendicular CSA of object (leading edge)
- density of fluid
- relative velocity
what is surface drag
- friction created when streamlines slid over surface of object
- boundrey layer is slowed
- nest layer slowed but to lesser extent
- laminar flow needs to be intact
- best at slow velocities
what is form drag
- high velocities
- high pressure zone develops at leading edge
- low pressure zone devlops at trailing edge
- pressure gradiant goes opp of motion (from high to low)
what is the lift force?
- perpendicular to oncoming flid flow
- perpendicular to drag force
- acts along y axis in local reference system
what is the bernoullis principle
fluid pressure inversly related tor fluid velocity
what happens to velocity and pressure during pos/neg angle of attack
- pos: HV/LP on top portion and LV/HP on bottom portion
- neg: LV/HP on top portion and HV/LP on bottom portion
what is the stall angle
- critical maximum angle of attack
- when lift force suddenly decreases to zero
what is the magnus effect
lift force on spinning objects
what happens to lift force during a top spin on a ball?
- boundrey layers start spinning with ball
- when boundrey layer is moving in same direction as streamlines HV/LP
- when boundrey layers are moving in opp direction as streamlines LV/HP
- ball will fall faster than just gravity acting on it b/c of downwards magnus force
what happens to lift force during back spin on a ball?
- same direction = HV/LP
- opp direction = LV/HP
- ball will curve upward if looking from side view b/c of upward force
- ball will curve to the left if looking from top view
terminal velocity is affected by…
5 of them
- streamlinedness
- CSA
- fluid density
- relative velocity
- weight
what can sydiver manipulate to have same VERTICAL position as another skydiver
- form drag
- perpendicular CSA
- flipped reference system so y axis = x axis in GRS
- drag force acts in x axis
what can a skydiver manipulate to have same HORIZONTALposition as another skydiver
lift force
- flipped reference system so x axis = y axis in GRS
- lift force acts in y axis
