Fluids Flashcards
density of fluid formula
density = mass/volume
density of water
1000kg/m^3
1kg/L
1g/cm^3
1g/cc
what is specific gravity
density of a substance divided by the density of water
what is fluid pressure of a static fluid
avg force all the fluid molecules apply to a given surface area by continuously colliding with it
P = F/A (N/m^2)
is pressure a scalar quantity
yes
what is the pressure equation due to depth of submersion
Psub = p(density of fluid) x g (10m/s) x d
** note size or shape doesn’t matter
what is the pressure from the gas of earths atmosphere
pressure atm = 1x10^5Pa = 100kPa = 1 atm
if you go higher in the atmosphere pressure…
decreases
pressure of a vacuum is
0 Pa
at any depth in a fluid there will be hydrostatic pressure due to depth of fluid on top (remember air is a fluid!) what is the equation for pressure total
Pt = Surface + pgy
what is gauge pressure
what a gauge would read, doesn’t include atmospheric pressure
p gauge = Pt - Patm
what is pascals principle
any external pressure applied to a fluid is transmitted undiminished throughout the entire fluid
what is the buoyant force
an object submerged in fluid experiences an upward force due to the difference in pressure between the top and bottom of an object
what is archimedes principle
buoyant force = weight of fluid displaced by the object
Fb = m fluid displaced x g
what is the formula for buoyant force ***only true when object is submerged
Fb = Pfluid x Vobject submerged x g
if the density of a submerged object is greater than the fluid
the object will sink
there is still buoyant force so it will feel lighter
if a submerged object as the same density as the fluid ti
experience neutral buoyancy and stay where it is
if the submerged object is less dense than the fluid it will experience
a rise upwards until it breaks through above the surface of the fluid
now some of it is outside the fluid reducing the volume submerged thus reducing the buoyant force
this continues until the buoyant force = the weight
then the object can float on the surface in equilibrium
equation to determine the fraction of an object submerged
Pobject/Pfluid
what is the centre of buoyancy and what should the centre of mass be in relation to it
centre of the volume of the object
for a boat to be stable the centre of mass must be below the centre of buoyancy
characteristics of ideal fluids
no viscosity incompressible no friction no change in density no turbulence
what is the continuity equation
Q(flow rate) = A1V1 = A2V2
*** this is for moving fluids aka hydrodynamics
what is Bernoulli’s equation
applies to fluids in motion at various heights in a pipe
law of conservation of energy except for fluids
P1 +1/2pv + pgh1 = P2 +1/2pv + pgh2
as we go higher up pressure
decreases
as velocity increases pressure
decreases - less time for the fluid to exert pressure
equation to use if there is a leak in a tank
v = square root of 2gy(depth)
what are Venturi tubes
air moves from a large area into a smaller one thus experiencing a faster velocity and consequently a decrease in pressure
the change in pressure affects the liquid in the U shaped tube which can be used to calculate pressure by applying the hydrostatic pressure equation to the fluid in the tube (P = Surface + pgy)
How are real fluids different from ideal fluids
They have viscosity and experience friction between their own molecules and with the pipe
They have turbulence
Always flow less
Ex. Blood
What is the pressure difference required to drive real fluid flow given by
Change in p = volume flow rate x resistance to flow
In non ideal fluid where will flow be slower in a pipe
Edges where there is friction with the wall
According to poiseuilles law for every 1 increase in radius flow increases
By 4
According to poiseuilles law an increase in viscosity and length would ____ flow rate
Increase
What is surface tension
Intensity of intermolecular forces
On the surface there is no force pulling up to cancel out the forces pulling on the liquid in the fluid which makes the fluid want to pull into itself and hold itself together at the surface
If molecules are more attracted to a container than the other water molecules what meniscus do you get
Concave - fluid climbs up the tube
What kind of meniscus do you get if the fluid is more attracted to itself than the container
A convex meniscus like in mercury
real fluids have viscosity and turbulence so we need a pressure difference to drive a fluid flow from one point to another given by
change in P between the 2 ends of the flow = Q(volume flow rate) x R (resistance to flow)
poiseuilles Law tells us for every 1 increase in radius the flow on a non ideal fluid will
increase by 4
flow is fastest in the centre of the pipe
*** know how to get units from this formula
