# Section 13.3 Fluids at Rest and in Motion - PowerPoint PPT Presentation

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## Section 13.3 Fluids at Rest and in Motion

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### Section 13.3 Fluids at Rest and in Motion Objectives Relate Pascal s principle to simple machines and occurrences. Apply Archimedes principle to buoyancy. – PowerPoint PPT presentation

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Title: Section 13.3 Fluids at Rest and in Motion

1
Section 13.3 Fluids at Rest and in Motion
• Objectives
• Relate Pascals principle to simple machines and
occurrences.
• Apply Archimedes principle to buoyancy.
• Apply Bernoullis principle to airflow.

2
FLUIDS AT REST
• If you have ever dived deep into a swimming pool
or lake, you know that your body, especially your
ears, is sensitive to changes in pressure.
• You may have noticed that the pressure you felt
was upright or tilted, but that if you swam
deeper, the pressure increased.
• Ideal Fluid fluid with no internal friction
among the particles.

3
FLUIDS AT REST
• Blaise Pascal a French physician, that noted
that the shape of a container had no affect on
the pressure at any given depth. He was the
first to discover that any change in pressure
applied to a confined fluid at any point is
transmitted undiminished throughout the fluid.
• Pascals Principle pressure applied to a fluid
is transmitted undiminished throughout it. Every
time you squeeze a tube of toothpaste you use
Pascals Principle.

4
FLUIDS AT REST
• Pascals Principle is applied in the operation of
machines that use fluids to multiply forces, as
in hydraulic lifts.
• P1 F1 / A1 and P2 F2 / A2
• Since pressure is transmitted without change P2
is the same as P1.
• So F1 / A1 F2 / A2 or F2 F1A2 / A1
• Do Practice Problem 23 p. 353
• F1 / A1 F2 / A2 or F2 F1A2 / A1
• 1600 / 1440 F / 72 F 1600(72) / 1440
• 80 N F F 80 N

5
SWIMMING UNDER PRESSURE
• When you are swimming, you feel the pressure of
the water increase as you dive deeper.
• This pressure is actually a result of gravity it
is related to the weight of the water above you.
• The deeper you go, the more water there is above
you, and the greater the pressure.
• Pressure Of Water on a Body the pressure that a
column of water exerts on a body is equal to the
density of water times the height of the column
times the acceleration due to gravity.
• P ?hg (? is small Greek letter rho)
• That formula works for all fluids.

6
SWIMMING UNDER PRESSURE
• The pressure of a fluid on a body depends on the
density of the fluid, its depth, and g.
• Buoyant Force is equal to the weight of the
fluid displaced by the object, which is equal to
the Density of the fluid in which the object is
immersed multiplied by the objects volume and
the acceleration due to gravity. It is the
upward force on an object immersed in fluid.
• Fbuoyant ?Vg Buoyant Force Density
Volume gravity
• Archimedes Greek scientist that found the
relationship that the buoyant force has a
magnitude equal to the weight of the fluid
displaced by the immersed object.
• Archimedes Principle states that an object
immersed in a fluid is buoyed up by a force (or
has an upward force) equal to the weight of the
fluid displaced by the object. It is important
to note that the buoyant force does not depend on
the weight of the submerged object, only the
weight of the displaced fluid.

7
SWIMMING UNDER PRESSURE
• If you want to know whether an object sinks or
floats, you have to take into account all of the
forces acting on the object.
• The buoyant force pushes up, but the weight of
the object pulls it down.
• The difference between the buoyant force and the
objects weight determines whether an object
sinks or floats.
• Go over the Sink or Float? Example p. 354-355
• An object will float if its density is less than
the density of the fluid in which it is immersed.

8
SWIMMING UNDER PRESSURE
• Ships can float because the hull is hollow and
large enough so the average density of the ship
is less than the density of water. You can
notice that a ship filled with cargo will be
submerged more than a ship with no cargo.
• Example 3 p. 356
• a. Fbuoyant ?Vg b. Fg mg ?Vg
Fapparent Fg Fb
• Fbuoyant 1000(.001)(9.8) Fg
2700(.001)(9.8) Fa 26.46 9.8
• Fbuoyant 9.8 N Fg 26.46 N
Fa 16.66 N
• Skip Practice Problems p. 356

9
FLUIDS IN MOTION BERMOULLIS PRINCIPLE
• Bernoullis Principle states that as the
velocity of a fluid increases, the pressure
exerted by that fluid decreases. Or when a fixed
quantity of fluid flows, the pressure is
decreased when the velocity increases.
• There are many common applications of Bernoullis
principle, such as paint sprayers and perfume
bottles.
• A gasoline engines carburetor, which is where
air and gas are mixed, is another common
application of Bernoullis principle.
• Part of the carburetor is a tube with a
constriction, as shown in figure 13-16b.
• Streamlines lines representing the flow of
fluids around objects.
• Skip 13.3 Section Review