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Forces in Fluids

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The ability of a fluid to exert an upward force on an object placed in it ... b. air pressure decreases as altitude increases. c. which has more pressure air or water? ... – PowerPoint PPT presentation

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Title: Forces in Fluids


1
Forces in Fluids
  • Chapter 13

2
Chapter 13
  • Buoyancy
  • Fluid Pressure
  • Forces and Pressures in Fluids
  • Pascals Principle
  • Bernouillis Principle
  • Archimedes Principle

3
Buoyancy
  • The ability of a fluid to exert an upward force
    on an object placed in it
  • Results in the apparent loss of weight

4
Buoyancy, contd
  • Archimedes Principle
  • The buoyant force on an object is equal to the
    weight of the fluid displaced by the object
  • (Displaced pushed aside)

5
Buoyancy, contd
  • Density and buoyancy
  • If an object is less dense than the fluid, it
    floats.
  • If an object is more dense than the fluid, it
    sinks.

6
Fluid Pressure
  • Fluid substance that assumes the shape of its
    container
  • Includes liquids and gases

7
Fluid Pressure, contd
  • Pressure is the result of force distributed over
    a given area
  • PF/A
  • SI units N/m2 pascal (Pa)
  • usually measured in kilopascals

8
Fluid Pressure, contd
  • Examples
  • What happens when you pick up a book with two
    fingers vs. your whole hand?
  • What happens when you walk with shoes on wet
    cement?

9
Fluid Pressure, contd
  • Pressure in fluids
  • Fluid pressure is determined by depth and type of
    fluid

10
  • Examples
  • a. water pressure increases as depth increases
  • b. air pressure decreases as altitude increases
  • c. which has more pressure air or water? Water or
    oil?
  • Equal in all directions
  • Example air pressure

11
Transmitting pressure in a fluid
  • Bernouillis Principle
  • As the speed of a fluid increases the pressure
    within the fluid decreases
  • What makes airplanes fly less pressure on top of
    wing because air moving faster over the wing ---
    creates lift

12
Forces and Pressures in Fluids
  • Transmitting pressure in a fluid
  • Pascals Principle
  • Change in the pressure at any point in a fluid is
    transmitted equally and unchanged in all
    directions throughout the fluid
  • examples pushing on toothpaste tube pushing on
    plastic water bottle

13
Pascals Principle, contd
  • Hydraulics applied Pascals Principle
  • Pressurized fluid acts on pistons of different
    sizes to change a force
  • Example hydraulic lift
  • F100 N F?
  • A10m A25m
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