Fluids

Question 1

Weight of a certain volume

Answer 1

rho(V)(g)

density x volume x gravity

Question 2

specific gravity

Answer 2

SG= density / density of water (1kg/m3)

sink or float

Question 3

standard pressure

Answer 3

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

pressure = Force/area
1 Pa= 1 N/ m^2
1 N= kg m/ s^2

Question 4

When two pressures acting on an object

Answer 4

Fnet = Pnet x A
Fnet = (P inside - Poutside)A

Question 5

atmospheric pressure and BP

Answer 5

inc Patm
dec hemoglobin affinity
inc boiling point (pressure above liquid inc)

Question 6

absolute hydrostatic pressure

Answer 6

P = Po - rho (g)(z)

Po= pressure at surface 
rho = density of 
g = gravity
z = depth of object

Question 7

Gauge pressure

Answer 7

Pgauge = P - Patm
when Patm = Po, then Pgauge = rho (g)(z)

P = Po - rho (g)(z)

Question 8

pascal’s principle

Answer 8

Hydraulic lift

P = F1/A1 = F2/A2

volume displaced at piston 1 = volume displaced at 2
V = A1D1 = A2D2

Question 9

Work in hydrostatics

Answer 9

Basically pascals principle?

result of constant pressure and change in volume
W= deltaP x V =

W = F1 A1 (D1/A1) 
W = F1D1
W = F2D2

Question 10

Archimedes Principle

Answer 10

buoyant force is = weight of displaced fluid

Fbuoy = (pfluid)(Vfluiddisp)(g) 
Fbuoy = (pfluid)(Vobjsub)(g) 

Fbuoy = weight of the block if it be floating
weight of an object = density x volume x gravity
= (p)(V)(g)

Question 11

Surface tension

Answer 11

caused by cohesion (liquid-liquid)

Ts =

Question 12

Adhesion

Answer 12

Caused by liquid-other

cause of meniscus and water droplets
concave- open top (adhesive > cohesive)
convex- open bottom (cohesive>adhesive)

Question 13

viscosity

Answer 13

nonconservative force

Question 14

Laminar flow

Answer 14

smooth, orderly flow

layers of fluid flow parallel- outer layer close to wall = slow

Question 15

Poiseulle Law

Answer 15

Rate of flow given by
Q = (pi)(r^4)(delta P) / 8nL

r= radius
n= viscosity
L= length
delta p = pressure gradient

Question 16

Suppose flow rate 100 cm3/s

• • double L?
• • double n?
• • double pressure?
• • double radius?

Answer 16

Q = (pi)(r^4)(delta P) / 8nL

• • 50
• • 50
• • 200
• • 1600

Question 17

Venturi effect

Answer 17

narrow pipe = greater linear speed of water = less static pressure on walls

Question 18

Turbulent flow

Answer 18

disorderly flow, causes eddies
can happen above fluid’s critical speed

critical speed =

Question 19

Flow rate constant in closed systems

continuity equation

Answer 19

Q = v1A1 = v2A2

linear speeds v1 & v2 vary- flow quick thru narrow and slow at wide parts
conservation of mass of fluids
keeps overall Q the same

Question 20

Bernoulli’s Equation

Answer 20

conservation of energy in closed system
ie- less movement = more static pressure = more energy

P1 + 1/2(p1)(v^2)1 + (p)(g)(h1) = P2 + 1/2(p2)(v^2)2 + (p)(g)(h2)

P1 = absolute pressure at point 1 
p1 = density at point 1
v1 = linear speed at point 1 
h1 = height at point 1 

sums dynamic 1/2(p1)(v^2)1
and static P1 & (p)(g)(h1)
pressures