Fluids

Question 1

density of fluid formula

Answer 1

density = mass/volume

Question 2

density of water

Answer 2

1000kg/m^3
1kg/L
1g/cm^3
1g/cc

Question 3

what is specific gravity

Answer 3

density of a substance divided by the density of water

Question 4

what is fluid pressure of a static fluid

Answer 4

avg force all the fluid molecules apply to a given surface area by continuously colliding with it
P = F/A (N/m^2)

Question 5

is pressure a scalar quantity

Answer 5

yes

Question 6

what is the pressure equation due to depth of submersion

Answer 6

Psub = p(density of fluid) x g (10m/s) x d

** note size or shape doesn’t matter

Question 7

what is the pressure from the gas of earths atmosphere

Answer 7

pressure atm = 1x10^5Pa = 100kPa = 1 atm

Question 8

if you go higher in the atmosphere pressure…

Answer 8

decreases

Question 9

pressure of a vacuum is

Answer 9

0 Pa

Question 10

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

Answer 10

Pt = Surface + pgy

Question 11

what is gauge pressure

Answer 11

what a gauge would read, doesn’t include atmospheric pressure
p gauge = Pt - Patm

Question 12

what is pascals principle

Answer 12

any external pressure applied to a fluid is transmitted undiminished throughout the entire fluid

Question 13

what is the buoyant force

Answer 13

an object submerged in fluid experiences an upward force due to the difference in pressure between the top and bottom of an object

Question 14

what is archimedes principle

Answer 14

buoyant force = weight of fluid displaced by the object

Fb = m fluid displaced x g

Question 15

what is the formula for buoyant force ***only true when object is submerged

Answer 15

Fb = Pfluid x Vobject submerged x g

Question 16

if the density of a submerged object is greater than the fluid

Answer 16

the object will sink

there is still buoyant force so it will feel lighter

Question 17

if a submerged object as the same density as the fluid ti

Answer 17

experience neutral buoyancy and stay where it is

Question 18

if the submerged object is less dense than the fluid it will experience

Answer 18

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

Question 19

equation to determine the fraction of an object submerged

Answer 19

Pobject/Pfluid

Question 20

what is the centre of buoyancy and what should the centre of mass be in relation to it

Answer 20

centre of the volume of the object

for a boat to be stable the centre of mass must be below the centre of buoyancy

Question 21

characteristics of ideal fluids

Answer 21

no viscosity 
incompressible 
no friction
no change in density 
no turbulence

Question 22

what is the continuity equation

Answer 22

Q(flow rate) = A1V1 = A2V2

*** this is for moving fluids aka hydrodynamics

Question 23

what is Bernoulli’s equation

Answer 23

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

Question 24

as we go higher up pressure

Answer 24

decreases

Question 25

as velocity increases pressure

Answer 25

decreases - less time for the fluid to exert pressure

Question 26

equation to use if there is a leak in a tank

Answer 26

v = square root of 2gy(depth)

Question 27

what are Venturi tubes

Answer 27

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)

Question 28

How are real fluids different from ideal fluids

Answer 28

They have viscosity and experience friction between their own molecules and with the pipe
They have turbulence
Always flow less
Ex. Blood

Question 29

What is the pressure difference required to drive real fluid flow given by

Answer 29

Change in p = volume flow rate x resistance to flow

Question 30

In non ideal fluid where will flow be slower in a pipe

Answer 30

Edges where there is friction with the wall

Question 31

According to poiseuilles law for every 1 increase in radius flow increases

Answer 31

By 4

Question 32

According to poiseuilles law an increase in viscosity and length would ____ flow rate

Answer 32

Increase

Question 33

What is surface tension

Answer 33

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

Question 34

If molecules are more attracted to a container than the other water molecules what meniscus do you get

Answer 34

Concave - fluid climbs up the tube

Question 35

What kind of meniscus do you get if the fluid is more attracted to itself than the container

Answer 35

A convex meniscus like in mercury

Question 36

real fluids have viscosity and turbulence so we need a pressure difference to drive a fluid flow from one point to another given by

Answer 36

change in P between the 2 ends of the flow = Q(volume flow rate) x R (resistance to flow)

Question 37

poiseuilles Law tells us for every 1 increase in radius the flow on a non ideal fluid will

Answer 37

increase by 4
flow is fastest in the centre of the pipe

*** know how to get units from this formula