# Chapter VIII Fluid Mechanics

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24 Οκτ 2013 (πριν από 4 χρόνια και 8 μήνες)

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Chapter VIII

Fluid Mechanics

Density and Pressure

Pressures in a fluid at Rest

Buoyancy

Fluid Flow

A
ﬂuid

is a collection of molecules that are randomly arranged and
held together by weak cohesive forces and by forces exerted by
the walls of a container.

Both liquids and gases are
ﬂuids
.

A. Density and Pressure

F

=

force

A
=

surface area

p = Pressure

T
he density of a substance is
deﬁned

as its mass per unit
volume

= m/V

= dencity

m = mass

V = Volume

T
he pressure
p

at a depth h below the surface
of a liquid open to the

atmosphere is greater
than atmospheric pressure

(p
o
)

by an amount

gh

B. Pressures in a Fluid at Rest

Pascal’s law: A change in the pressure

applied to a
ﬂuid

is
transmitted undiminished to every point of the
ﬂuid

and to the
walls of the container.

Because the increase in
pressure is the same on

the
two sides, a small force F
l

at
the left produces a much
greater force F
2

at the right

C. Buoyancy

Have you ever tried to push a beach ball under water?

This is extremely
difﬁcult

to

do because of the large upward force
exerted by the water on the ball.

The upward

force exerted by water on any immersed object is
called a buoyant force
.

1. Totally Submerged Object

B = Buoyant force

F
g

= Force of gravity/weight

2. Floating Object

F
g

= B

o

V
o

g =

f

V
f

g

V
f

is the volume of the
ﬂuid

displaced by the
object (this

volume is the same as the
volume of that part of the

object that is
beneath the

ﬂuid

level)

Ideal ﬂuid

D. Fluid Flow

1.
The
ﬂuid

is
nonviscous
. In a
nonviscous

ﬂuid
, internal friction
is neglected.

An object moving through the
ﬂuid

experiences no
viscous force.

2.
The
ﬂow

ﬂow
, the velocity of the
ﬂuid

at each

point remains constant.

3.
The
ﬂuid

is incompressible. The density of an incompressible
ﬂuid

is constant.

4.
The
ﬂow

is
irrotational
. In
irrotational

ﬂow
, the
ﬂuid

has no
angular momentum about any point

A
1

v
1

= A
2

v
2

= constant

The equation of continuity

Bernoulli’s Equation

MEKANIKA FLUIDA

Fluida Statik

Fluida merupakan istilah untuk zat alir.

Fluida statik adalah fluida yang tidak bergerak.

Contoh fluida statik misalnya air di gelas, air di
kolam renang, dan air danau.

1. Fluida ideal

Fluida ideal adalah fluida yang memiliki ciri
-
ciri sebagai berikut.

a. tidak kompresibel (volumenya tidak berubah karena perubahan
tekanan)

b. berpindah tanpa mengalami gesekan (viskositasnya nol)

2. Fluida sejati

Fluida sejati memiliki ciri
-
ciri sebagai berikut.

a. kompresibel

b. berpindah dengan mengalami gesekan (viskositasnya tertentu)

1. Kohesi dan Adhesi

Gaya kohesi adalah gaya tarik
-
menarik antarmolekul sejenis.