Download Pressure - Jay Mathy Science Wiki

Chapter 9
Fluid
Dynamics
9.3
The density of a substance of uniform
composition is defined as mass per unit
volume
m
ρ=
V
Molten
Granite
Water
9.3
Common Density Units and Substances
Volume: 1 cm3 = 1 ml
1000 ml = 1000 cm3 = 1 liter
1 m3 = 1,000,000 cm3
1 m3 = 35.3 ft3
1 gallon = 231 in3
Density: 1 gram/cm3 = 1000
kg/m3 = “62.4 lb/ft3”
Substance
g/ mL
1.  Water
1.0
2.  Glycerin 1.3
3.  Iron
7.9
4.  Silver
10.5
5.  Lead
11.3
6.  Gold
19.3
7.  Platinum
8.  Air
21.4
.0013
Pressure is defined as force per unit
area
F
P=
A
Units:
lb /in2 = PSI
N/m2 = Pascal (Pa)
Hydrostatic Pressure
1.  Fluids exert pressure in all directions
2.  Fluids exerts pressure perpindicularly
to any surface that it contacts
1.
2.
Variation of “P” w/ Depth
1.  All points at same depth have = Pressure
2.  As depth increases , P increases but why?
F
mg
P=
a)
P =
A
A
m
ρ
=
→
m
=
ρ
V
b)
A block of fluid in
a fluid!!!
V
ρ
g(A • y)
c)
P =
A
P = ρgΔy
y
F
F
Absolute Pressure
Takes into account air
pressure above water plus the
pressure from the water!
P0 = 1 x 105 Pa
P = P 0 + ρgh
absolute
P = 3 x 105 Pa
Sometimes called
gauge pressure
Buoyancy:the difference in pressure on the upper and lower surfaces
of an object immersed in a liquid results in an upward force on the
object
Archimedes’
Principle:
“ Any submerged body
will be buoyed up by a
force equal to the
weight of the fluid
displaced!”
Fb = ρVg
FB
FW
Boat weighs 20 tons, put it
into the beaker and collect
the run -off water
20 ton boat =20tons water
displaced!!!
9.6
Fluid Flow Continuity:the flow rate of
a liquid through its cross section is the
same at any point along its path
A1v1 = A2v 2
9.7
Bernoulli’s Principle where fluid flow
is fast, internal pressure is low, and vice
versa. But Why???
9.7
Conservation of Work Energy
Theorem Applied to an airplane wing
W=KE + PE
Work in + Potential
energy at the
bottom + kinetic
energy and the
bottom =
1 2
P + ρv + ρgy = k
2
Work out +
Potential energy at
the top + Kinetic
energy at the top.