Introduction To Fluids Fluids Fluids are substances that can

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Introduction To

• Fluids

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Fluids

• Fluids are substances that can flow.
• Fluids are liquids and gases, and even some
  solids.
• In Physics B, we will limit our discussion of
  fluids to substances that can easily flow, such
  as liquids and gases.

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Density

• ? m/V
• ? density (kg/m3)
• m mass (kg)
• V volume (m3)
• Units
• kg/m3

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Sample Problem

• Given that water has a density of 1,000 kg/m3,
  calculate the mass of a barrel full of water.
  Assume that the barrel has a diameter of 1.0 m
  and a height of 1.5 m.

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Sample Problem

• Given that water has a density of 1,000 kg/m3,
  calculate the mass of a barrel full of water.
  Assume that the barrel has a diameter of 1.0 m
  and a height of 1.5 m.

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Sample Problem

• Given that water has a density of 1,000 kg/m3,
  calculate the mass of a barrel full of water.
  Assume that the barrel has a diameter of 1.0 m
  and a height of 1.5 m.

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Sample Problem

• Given that water has a density of 1,000 kg/m3,
  calculate the mass of a barrel full of water.
  Assume that the barrel has a diameter of 1.0 m
  and a height of 1.5 m.

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Pressure

• P F/A
• P pressure (Pa)
• F force (N)
• A area (m2)
• Pressure unit Pascal
• 1 Pa N/m2
• Atmospheric pressure is about 101,000 Pa

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Sample Problem

• Calculate the net force on an airplane window if
  cabin pressure is 90 of the pressure at sea
  level, and the external pressure is only 50 of
  that at sea level. Assume the window is 0.43 m
  tall and 0.30 m wide.

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Sample Problem

• Calculate the net force on an airplane window if
  cabin pressure is 90 of the pressure at sea
  level, and the external pressure is only 50 of
  that at sea level. Assume the window is 0.43 m
  tall and 0.30 m wide.

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Sample Problem

• Calculate the net force on an airplane window if
  cabin pressure is 90 of the pressure at sea
  level, and the external pressure is only 50 of
  that at sea level. Assume the window is 0.43 m
  tall and 0.30 m wide.

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Sample Problem

• Calculate the net force on an airplane window if
  cabin pressure is 90 of the pressure at sea
  level, and the external pressure is only 50 of
  that at sea level. Assume the window is 0.43 m
  tall and 0.30 m wide.

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Pressure

• The force on a surface caused by pressure is
  always normal to the surface.
• The pressure of a fluid is exerted in all
  directions, and is perpendicular to the surface
  at every location.

balloon
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The Pressure of a Liquid

• P ?gh
• P pressure (Pa)
• ? density (kg/m3)
• g acceleration constant (9.8 m/s2)
• h height of liquid column (m)

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Absolute Pressure

• P Po ?gh
• p pressure (Pa)
• po atmospheric pressure (Pa)
• ?gh liquid pressure (Pa)
• Po is atmospheric pressure.
• P is commonly referred to as absolute pressure,
  and includes atmospheric pressure.

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Gauge Pressure

• Gauge pressure is due to a fluid contained in a
  container and excludes atmospheric pressure.

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Sample Problem

• Calculate the pressure at the bottom of a 3 meter
  (approx 10 feet) deep swimming pool (a) due to
  the water and (b) due to the water plus the
  atmosphere.

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Sample Problem

• Calculate the pressure at the bottom of a 3 meter
  (approx 10 feet) deep swimming pool (a) due to
  the water and (b) due to the water plus the
  atmosphere.

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Sample Problem

• Calculate the pressure at the bottom of a 3 meter
  (approx 10 feet) deep swimming pool (a) due to
  the water and (b) due to the water plus the
  atmosphere.

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Sample Problem
Area of piston 8 cm2 Weight of piston 200 N
25 cm
A

• What is the absolute pressure at point A?

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Sample Problem
Area of piston 8 cm2 Weight of piston 200 N
25 cm
A

• What is the absolute pressure at point A?

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Sample Problem
Area of piston 8 cm2 Weight of piston 200 N
25 cm
A

• What is the absolute pressure at point A?

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Sample Problem
Area of piston 8 cm2 Weight of piston 200 N
25 cm
A

• What is the absolute pressure at point A?

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Sample Problem
Area of piston 8 cm2 Weight of piston 200 N
25 cm
A

• What is the absolute pressure at point A?

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Floating is a type of equilibrium
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Floating is a type of equilibrium

• Archimedes Principle a body immersed in a
  fluid is buoyed up by a force that is equal to
  the weight of the fluid displaced.
• Buoyant Force the upward force exerted on a
  submerged or partially submerged body.

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Calculating Buoyant Force

• Fbuoy ?Vg
• Fbuoy the buoyant force exerted on a submerged
  or partially submerged object.
• V the volume of displaced liquid.
• ? the density of the displaced liquid.
• Buoyant force is enough to float iron ships,
  automobiles, and brick houses!

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Parking in St. Bernard Parish after Hurricane
Katrina
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Parking in St. Bernard Parish after Hurricane
Katrina
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Parking in St. Bernard Parish after Hurricane
Katrina
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Mobile Homes in St. Bernard Parish after
Hurricane Katrina
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Mobile Homes in St. Bernard Parish after
Hurricane Katrina
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Buoyant force on submerged object
Note if Fbuoy lt mg, the object will sink deeper!
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Buoyant force on submerged object
SCUBA divers use a buoyancy control system to
maintain neutral buoyancy (equilibrium!)
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Buoyant force on floating object
If the object floats, we know for a fact Fbuoy
mg!
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Sample problem

• Assume a wooden raft has 80.0 of the density of
  water. The dimensions of the raft are 6.0 meters
  long by 3.0 meters wide by 0.10 meter tall. How
  much of the raft rises above the level of the
  water when it floats?

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Sample problem

• Assume a wooden raft has 80.0 of the density of
  water. The dimensions of the raft are 6.0 meters
  long by 3.0 meters wide by 0.10 meter tall. How
  much of the raft rises above the level of the
  water when it floats?

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Sample problem

• Assume a wooden raft has 80.0 of the density of
  water. The dimensions of the raft are 6.0 meters
  long by 3.0 meters wide by 0.10 meter tall. How
  much of the raft rises above the level of the
  water when it floats?

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Sample problem

• Assume a wooden raft has 80.0 of the density of
  water. The dimensions of the raft are 6.0 meters
  long by 3.0 meters wide by 0.10 meter tall. How
  much of the raft rises above the level of the
  water when it floats?

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Buoyancy Lab

• Using the equipment provided, verify that the
  density of water is 1,000 kg/m3.
• Report (due Tuesday) must include
• Free body diagrams.
• All data.
• Calculations.

water
air
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Reading a Venier Caliper
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Reading a Venier Caliper
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Reading a Venier Caliper
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Reading a Venier Caliper
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Sample problem

• You want to transport a man and a horse across a
  still lake on a wooden raft. The mass of the
  horse is 700 kg, and the mass of the man is 75.0
  kg. What must be the minimum volume of the raft,
  assuming that the density of the wood is 80 of
  the density of the water.

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Fluid Flow Continuity

• Conservation of Mass results in continuity of
  fluid flow.
• The volume per unit time of water flowing in a
  pipe is constant throughout the pipe.

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Fluid Flow Continuity

• A1v1 A2v2
• A1, A2 cross sectional areas at points 1 and 2
• v1, v2 speed of fluid flow at points 1 and 2

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Fluid Flow Continuity

• V Avt
• V volume of fluid (m3)
• A cross sectional areas at a point in the pipe
  (m2)
• v speed of fluid flow at a point in the pipe
  (m/s)
• t time (s)

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Sample problem

• A pipe of diameter 6.0 cm has fluid flowing
  through it at 1.6 m/s. How fast is the fluid
  flowing in an area of the pipe in which the
  diameter is 3.0 cm?

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Sample problem

• Suppose the current in a river is moving at 0.20
  meters per second where the river is 12 meters
  deep and 10 meters across. If the depth of the
  river is reduced to 1.5 meters at an area where
  the channel narrows to 5.0 meters, how fast will
  the water be moving through this narrow region?

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Sample problem

• How much water per second is flowing in the river
  described in the previous problem?

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Bernoullis Theorem

• The sum of the pressure, the potential energy per
  unit volume, and the kinetic energy per unit
  volume at any one location in the fluid is equal
  to the sum of the pressure, the potential energy
  per unit volume, and the kinetic energy per unit
  volume at any other location in the fluid for a
  non-viscous incompressible fluid in streamline
  flow.
• All other considerations being equal, when fluid
  moves faster, the pressure drops.

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Bernoullis Theorem

• P ? g h ½ ?v2 Constant
• P pressure (Pa)
• ? density of fluid (kg/m3)
• g gravitational acceleration constant (9.8 m/s2)
• h height above lowest point (m)
• v speed of fluid flow at a point in the pipe
  (m/s)

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Sample Problem

• Knowing what you know about Bernouillis
  principle, design an airplane wing that you think
  will keep an airplane aloft. Draw a cross section
  of the wing.

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Announcements 5/24/2013

• 6th period only pass photoelectric redo forward
  if I didnt get it yesterday.
• Buoyancy lab is due today. Put in folders.
• Fluid dynamics project you do today is due
  tomorrow, so work efficiently.

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URLs of interest

• Katrina and the Mississippi River Gulf Outlet
• http//www.mvn.usace.army.mil/ChannelSurveys/surve
  y.asp?prj_id15
• http//en.wikipedia.org/wiki/Mississippi_River_Gul
  f_Outlet
• http//www.cclockwood.com/stockimages/hurricanekat
  rina_MississippiGulfOutlet.htm
• http//www.washingtonpost.com/wp-dyn/content/artic
  le/2005/09/13/AR2005091302196.html
• http//www.saveourwetlands.org/mrgohastogo.html

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URLs of interest

• Hurricanes - classification
• http//www.ohsep.louisiana.gov/hurricanerelated/HU
  RRICANECATEGORIES.htm
• http//www.nhc.noaa.gov/aboutsshs.shtml
• Hurricanes - behavior
• http//ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hurr/
  home.rxml
• http//science.howstuffworks.com/hurricane.htm

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