Pressure

• Fluids are fascinating and awesome
• Fluids are the area of expertise of the speaker as an engineer in fluid dynamics
• Anything that flows - liquid or gas - is a fluid
• Physicists and engineers can design things like pressure sensors, hydraulic pumps, and even airplanes using their knowledge of fluids
• Density


  A different quality used to describe fluids, rather than mass. It is mass divided by volume, measured in kilograms per meters cubed.
• Pressure


  Force applied per unit area, measured in Pascals (Newtons per meters squared)
• Fluids apply pressure in every direction
• The average air pressure at sea level is 101,325 Pascals
• Calculating pressure of a fluid at a given depth

  Fluid density x gravitational acceleration x distance to surface
• Pascal's Principle


  If you apply pressure to a confined fluid, the pressure in every part of the fluid increases by that amount
• Applying pressure to a piston on one side of a fluid-filled tube

  Exerts the same pressure on the piston on the other side of the tube
• Ratio of output force to input force in a hydraulic system

  Equal to the ratio of output area to input area
• Manometer


  A U-shaped tube with a fluid inside, used to measure pressure differences
• Gauge pressure


  The difference between atmospheric pressure and the pressure inside a container
• Absolute pressure


  The atmospheric pressure plus the gauge pressure
• Barometer


  A device that measures atmospheric pressure, using a mercury-filled tube
• At standard atmospheric pressure, the mercury in a barometer tube will be 76 centimeters high
• Archimedes' Principle


  The volume of fluid displaced by an object is equal to the object's volume
• Archimedes discovered this principle while taking a bath, leading him to run naked through the streets yelling "Eureka!"
• Buoyant force


  The upward force exerted by a fluid on an object immersed in it, equal to the weight of the fluid displaced by the object
• An object denser than water


  Sinks to the bottom of the water
• An object less dense than water

  Floats on the surface of the water
• Pressure


  Force divided by area
• Pascal


  Standard unit of pressure, 1 newton per square meter
• Kilopascal


  1000 pascals
• Atmospheric pressure (1 atm)

  101.3 kilopascals
• Exerting a force over an area

  Pressure is applied throughout that area
• Increasing the area with the same force

  Pressure decreases
• Increasing the force


  Pressure increases
• Increasing the area


  Pressure decreases
• Calculating pressure of a 15 kg rectangular block

  1. Find weight force (mg)

  2. Find area of block bottom

  3. Divide force by area to get pressure
• Calculating pressure in a closed rectangular container filled with water

  1. Find density of water

  2. Find volume of container

  3. Calculate pressure using formula
• Calculating pressure in a closed cylindrical container filled with fluid

  1. Find density of fluid using specific gravity

  2. Calculate pressure using formula