3.2.2.6 Fluid mechanics Flashcards
fluid friction (drag) laminar
flowing of air or water past an object
depends on:
1. laminar flow (flow in layers) -> assisted by streamlining
2. smooth
fluid friction (drag) vortices
vortices formed fluid doesnt flow smoothly
bits of fluid flung randomly sideways
cause drag
bits of fluid dragged along with moving object (cycling helmet)
air resistance is dependent on..
3 things
- size
- shape
- speed of object
fluid mechanics
study of an object/human body travelling through any liquid or gas
fluid environment can affect variety of sports
1. drag 2. upward lift force 3. downward life force
fluid friction (drag)
force act opposite direction to motion = slow down
greater velocity of body travel in fluid = greater drag
depends on laminar flow (streamlining assists)
fluid friction depends on:
4 things
of moving object:
- shape (streamlined/aerodynamic = reduce drag)
- cross sectional area (larger= increase drag)
- velocity
- surface characteristics
examples of factors affecting fluid friction
e. g. cyclist change body position (swimmer also) leans forward /crouches/tucks arms in = decrease cross sectional area = less of their body exposed to air
e. g. cyclist wear lycra, swimmer wear hats (surface characteristics) = reduce surface drag - cycle at high speed
e. g. shape of helmets for cyclists, shape of sports vehicles car/bike curved cars - less turbulence - lamina flow
e. g. cyclist wear streamlined helmet = reduce turbulence - lamina flow
lamina flow
air flows smoothly around the object
smooth flowing of air or water past an object
flowing in layers
2 types of drag:
- surface drag
2. form drag (shape drag)
surface drag
friction between surface of an object and the fluid environment
-swimmers =specialised clothing & shave = reduce SD
form drag (shape drag)
impact of fluid env on an object
forces affecting leading edge of an object increase form drag and forces affecting trailing edge reduces form drag (streamlining)
swimmer = reduce form drag = thinest/straightest form as move through water
cyclist = reduce form drag through drafting= large form drag offers less turbulent air for anything following e.g. slipstream
high values of fluid friction
sports person/vehicle moving through water = high
= fluid friction is critical factor governing speed
drafting in cycling
wind hits 1st cyclist = gos round the sides = pockets of air behind them = the effect is greater the closer you are
shuttle cock example
turbulent flow = increase air resistance
low mass and large drag force (due to shape/holes/feathers)
drag is low when
3 things
- object moving slow
- smooth surface
- high mass
impact of fluid friction examples
e. g. sprinter/games players, fluid friction = much less than friction effect/weight (streamlining less important)
e. g. shot/hammer in flight = fluid friction much less than weight, angle of release 45 degrees
turbulent flow/vortex flow
vortices formed fluid doesnt flow smoothly
bits of fluid flung randomly sideways = drag
bits of fluid dragged along with moving object (cycle helmet)
Bernoulli principle
air molecules exert less pressure the faster they travel
air molecules exert more pressure the slower they travel
create a lift force = force causing body to move in perpendicular direction to direction of travel= more lift of projectile = longer stay in air - further horizontal distance travel
AEROFOIIL
angle of attack (AofA)
angle travelling through air
tilt of projectile relative to air flow
AofA increase too much = drag increase - projectile stall optimum angle (25-40)
pressure vs speed
moving slower = less distance to travel = more pressure
moving faster = further to travel = less pressure
downward lift (racing car)
move faster underneath = less pressure, want to move slower on top = more pressure = downward force
drag force
force that acts in opposition to motion
negative effect on velocity
streamlining
shaping a body so it can move effectively and quickly through a fluid
3 factors that increase/reduce drag
- velocity of moving body: faster = greater drag = greater AR (streamline)
- cross sectional area: large = increase, crouching down in cycling = travel faster
- shape/surface characteristics: streamlined/aerodynamic reduces drag e.g. speed skier (helmet), cycling helmets
badminton shuttlecock = larger drag from AR = lose speed quickly
lift force
causes body to move perpendicular to direction of travel
aerofoil
shape/object where air over the top travels further than the bottom
object has to travel further
travels at a faster speed
exerts less pressure
object has to travel less distance
travels at a slower speed
exerts more pressure
