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
    on your ears did not depend on whether your head
    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
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