# Fluid Mechanics

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24 Οκτ 2013 (πριν από 4 χρόνια και 6 μήνες)

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Newtonian Fluids

Gases are considered
compressible fluids

Liquids are considered
incompressible fluids

Another thing we pretend is true because the
compression is usually a negligible amount

Non
-
Newtonian fluids do not always act predictably

Pascal's Principles

External pressure applied to a fluid will be applied
uniformly throughout the fluid

F₁/A₁ = F₂/A₂

F₁/A₁ = F₂/A

50
Newtons

is applied to pump
a squirt gun with a cylinder
surface area of .01 square
meters. How much force does
it take to plug the barrel of the
squirt gun if the area of the
opening is 0.001 square
meters?

Does this obey the law of
conservation of energy?

Static Pressure and Depth

F=mg and the mass =
ρ
V

ρ

= density

V=area of the cross section x height

So F=
ρ
gV
=

ρ
g
Ah

P

= F/A=
ρ
gh

*for a uniform shape

Explain this phenomenon:

Relating KE, GPE, and existing P

From conservation of energy we can derive Bernoulli’s
equation:

P₁ +
ρ
gh
₁ + 1/2

ρ
v₁² = P₂ +
ρ
gh
₂ + 1/2

ρ
v₂²

Vocabulary

Conditions

Isobaric

constant pressure

Isothermic

constant temperature

no heat is added or removed from the
system; this is an important distinction from
isothermic

Laminar Flow

smooth movement of fluid without
turbulence (this is an important assumption of
Bernoulli’s equation)

Turbulent Flow

irregular movement of fluid where the
fluid may be working against parts of its own movement

The gas is composed of many molecules that are
relatively far apart

As a whole the molecules act according to the laws of
motion but individually their motion is random

Molecules undergo elastic collisions

Forces between molecules have no effect except during
a collision

The gas is a pure substance

The gas and the walls of the container are not
exchanging thermal energy

Ideal Gas Law

P₁V₁/T

= P₂V₂/T

or

PV=
nRT

Pressure x Volume =

number of Moles of the substance x Universal Gas Constant x
Temperature in Kelvin

0⁰ Kelvin =
-
273

⁰ Celsius

Pressure is in
Pascals

(Pa) or Nm² (1 Pa= 1 Nm²)

R= 8.31 joules per mole kelvin

Relating
P₁V₁/T ₁ = P₂V₂/T ₂
to your
experiences:

What happens when you heat up a closed container?

What happens to temperature when you decrease the
pressure in a spray can?

How might an air conditioner work?

Does opening the refrigerator door cool off the
kitchen?

How does the steamboat toy work?

What does an increase in temperature do to the
pressure?

How is pressure related to force?

m

a

=
m

a

The mass of the boat is accelerated according to
Newton’s third law. The force created by the pressure in
the steam chamber results in equal and opposite forces
acting on the boat and the water.