fluids

Question 1

density

Answer 1

p=m/V, scalar quantity

p(rho) is density, m is mass, and V is volume; units: Kg/m^3 or g/mL = g/cm^3

Question 2

density of water

Answer 2

1 g/cm^3= 1000 kg/m^3

Question 3

weight of volume of a fluid

Answer 3

F=pVg

seen often with buoyancy problems

Question 4

specific gravity

Answer 4

SG= p/ 1 (g/cm^3), unit less

good for determining if something will sink or float in water

Question 5

Pressure

Answer 5

a ratio of the force per unit area; scalar quantity
P= normal force vector (F)/ area (A)
unit: 1 pascal (Pa)= 1 N/m^2

Question 6

other units for pressure

Answer 6

1.013 x 10^5 Pa = 760 mmHg = 760 torr =1 atm

Question 7

Absolute pressure

Answer 7

sum of all pressures at a certain point within a fluid; it is equal to the pressure at the surface of the fluid plus the pressure due to the fluid itself

Question 8

absolute hydrostatic pressure

Answer 8

pressure on an object submerged in a fluid
P (absolute pressure)= incident or ambient pressure, the pressure at the surface (Po) + pgz
(z=depth of the object)
in open air, Po is 1 atm

Question 9

gauge pressure

Answer 9

the difference between absolute pressure and atmospheric pressure. in liquids, gauge pressure is caused by the weight of the liquid above the point in measurement
P gauge= P-Patm= (Po+pgz)-Patm

Question 10

hydrostatics

Answer 10

the study of fluids at rest and the forces and pressures associated with standing fluids

Question 11

Pascal’s principle

Answer 11

states that a pressure applied to an incompressible fluid will be distributed undiminished throughout the entire volume of the fluid
P (pressure)= F1/A1=F2/A2
V (volume)= A1d1=A2d2

Question 12

work as a product of constant pressure and volume change

Answer 12

it is an isobaric process

W=PxdeltaV= F1d1=F2d2

Question 13

Archimede’s principle

Answer 13

governs the buoyant force. when an object is placed in a fluid, the fluid generates a buoyant force against the object that is equal to the weight of the fluid displaced by the object

Question 14

buoyant force

Answer 14

Fbuoy=p(fluid)V(fluid displaced)g=p(fluid)V(submerged)g

Question 15

what will happen when an object is more dense then the fluid that it is in?

Answer 15

the object will be completely submerged because the volume of displaced fluid will not exert a buoyant force equal to the weight of the object, so the object will sink to the bottom

Question 16

what happens to an object that is placed in a fluid that’s density is greater then the object?

Answer 16

it will sink into the fluid only to the point at which the volume of displaced fluid exerts a force that is equal to the weight of the object

Question 17

cohesion

Answer 17

the attractive force that a molecule of liquid feels toward other molecules of the same liquid; gives rise to surface tension (liquid that forms a thin but strong layer)

Question 18

adhesion

Answer 18

the attractive force that a molecule of the liquid feels toward the molecules of some other substance

Question 19

meniscus

Answer 19

curved surface in which the liquid “crawls” up the side of a container; happens when the adhesive forces are greater then the cohesive forces

Question 20

fluid dynamics

Answer 20

the study of fluids in motion

Question 21

viscosity (eta)

Answer 21

the resistance of a fluid to flow, increase to this increases the viscous drag; should be ignored on questions unless other wise stated
units: (Pa)(s)=(Nxs)/m^2

Question 22

viscous drag

Answer 22

a nonconservative force that is analogous to air resistance. objects moving through the liquid will experience this viscous drag

Question 23

ideal fluids

Answer 23

have no viscosity and are described as inviscid

Question 24

what happens to liquids with higher viscosity in regards to energy?

Answer 24

they lose more energy then liquids with lower viscosity`

Question 25

laminar flow

Answer 25

smooth and orderly, and is often modeled as layers of fluid that flow parallel to each other, however the layers will not necessarily have the same linear speed

Question 26

poiseuille’s law

Answer 26

used with laminar flow through a pipe or confined space
Q= (pi r^4 deltaP)/ (8 eta L)

Q=flow rate 
r= radius of the tube 
deltaP= pressure gradient 
eta=viscosity of the fluid 
L=length of the pipe

Question 27

turbulent flow

Answer 27

rough and disorderly. turbulence causes the formation of eddies; lose lots of energy due to frictional forces

Question 28

eddies

Answer 28

swirls of fluid of varying sizes occurring typically on the downstream side of an obstacle, occurs when the speed of the fluid exceeds the critical speed

Question 29

critical speed

Answer 29

depends on the physical properties of the fluid, such as viscosity and the diameter of the tube
vc= (Nr x eta)/ (pD)

D=diameter 
vc=critical speed 
Nr=dimensionless constant (Reynolds number) 
eta= viscosity of the fluid 
p=density of the fluid

Question 30

streamlines

Answer 30

indicate the pathways followed by tiny fluid elements

Question 31

linear speed

Answer 31

a measure of the linear displacement of fluid particles in a given amount of time

Question 32

continuity equation

Answer 32

Q= v1A1=v2A2

v=linear speeds of the fluid at point 1 and 2
A=areas at point 1 and 2
Q=flow rate

Question 33

Bernoulli’s Equation

Answer 33

an expression of conservation of energy for a flowing fluid; states that the static pressure and dynamic pressure will be constant between any two points in a closed system
P1+(1/2pv1^2)+pgh1=P2+(1/2pv2^2)+pgh2

P=absolute pressure of the fluid 
p=density 
v=linear speed
g=acceleration due to gravity 
h=height of the fluid above some datum

Question 34

dynamic pressure

Answer 34

1/2pv^2

Question 35

static pressure

Answer 35

P+pgh

Question 36

what generates more pressure, faster or slower moving fluids?

Answer 36

slower moving fluids will exert more static pressure

Question 37

Venturi effect

Answer 37

for a horizontal flow, there is an inverse relationship between pressure and speed, and in a closed system, there is a direct relationship between cross sectional area and pressure exerted on the walls of the tube