Fluids and Pressure

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Fluids and Pressure

• Chapter 3

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Fluids

• Any material that can flow and take the shape of
  its container
• Fluids include gases and liquids

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All Fluids Exert Pressure

• Remember Boyles Law

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Calculating Pressure

• Pressure Force / Area
• Area Force / Pressure
• SI unit for pressure is pascal
• Written 1 Pa
• Remember
• Force Newton
• Area m2

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Math Break

• Turn to Page 62
• Find the pressure exerted by 3,000N crate with an
  area of 2m2
• Hint Pressure Force / Area

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Solution

• Force 3000 N
• Area 2 m2
• Pressure ?
• Pressure 3000N / 2 m2
• 1,500 Pa

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Question 2

• Find the weight of a rock with an area of 10 m2
  that exerts a pressure of 250 Pa

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Solution

• Area 10 m2
• Force ?
• Pressure 250 Pa
• Force 250 Pa x 10 m2
• 2,500 N

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Atmospheric Pressure

• The small amount of pressure (weight) caused by
  the Atmosphere
• Approx 101,300 N or 101,300 Pa
• http//www.wfu.edu/physics/demolabs/demos/avimov/f
  luids/marshmallow_man/marshmallow_man.MPG

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Example
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Water Pressure

• Increases with depth
• Is denser than air so it exerts more pressure

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Fluids Flow from High Pressure to Low Pressure

• Think about drinking straws

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Pascal's Principle

• Pressure applied to an enclosed fluid is
  transmitted undiminished to every part of the
  fluid, as well as to the walls of the container.
• http//webphysics.davidson.edu/physlet_resources/b
  u_semester1/c23_pressure_pascal.html
• http//www.wfu.edu/physics/demolabs/demos/2/2b/2B2
  042.html

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Automobile Hydraulic Lift
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Quick Lab

• Page. 66
• Turn in question 6
• Page 64 Questions 1-3

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Buoyant Forces

• The upper force that fluids exert on an object

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Law of Archimedes

• The buoyant force is equal to the weight of the
  replaced liquid or gas.
• http//www.youtube.com/watch?vvJ36urazDu4

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Weight vs Buoyant Force

• Use figure 10 on page 69
• Draw 3 objects not listed in picture that would
• Sink, Float and Float on the surface of water
• Draw forces using arrows

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The Mystery of Floating Steel
Remember D m / v
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How Fish Float

• The swim bladder allows fish to change there
  density
• This allows them to float at different depths
• How does increasing volume affect the fishes
  floating?

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Page 71

• Quick Lab Ship-Shape
• Turn in Question 3
• Due Before the end of Class
• Homework Page 72 (1-3)

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Homework

• Page 72 Question (1-4)

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Bernoullis Principal

• As speed of a moving fluid increases, its
  pressure decreases
• Swiss Mathematician
• Example Shower Curtain

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Page 73

• Quick Lab
• Turn in a Diagram of results and Question 3
• Label High and low pressure
• Page 77 (1-4)

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Quick Lab

• b Hold one end of a small sheet of paper in
  both hands. Keep the held edge horizontal while
  the other end sags under its own weight. Blow
  steadily over the top of this horizontal edge.

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Terms To Know
The upward force that pushes against gravity

• The forward force produced by fling object
  (planes engine)

The fluid force the opposes motion of the object
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Wings are Not a Requirement for Flight
Curveball exhibit Bernoullis Principal
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Biplane
Airship
Jet
Glider
Pick any two of the following aircrafts and
compare and contrast them in terms of lift, drag,
thrust and gravity? What are the characteristics
of each that allow them to fly?
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Short Review

• Fluids in Pressure
• Pressure in Atmosphere
• Pressure under water
• Altitude and Pressure
• Buoyant Forces
• Sinking, Floating, Buoying up
• Archimedes Principle
• Density
• Bernoullis Principal
• Fluid speed effect pressure How?
• Airplane Terms

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Study Guide Time

• Test March 10th
• Lets Make As