PRESSURE TEST:

The emphasis will be only in the basics. Here is some help for your studying.
You should be able understand following type topics/consepts:

  • Pressure: definition, unit, calculations (P = F/A)
  • Liquid pressure: Think everyday applications or experiments that would show that the following is true.
      • Pressure in liquid increases with depth ( P=dhg; d = density of liquid).
      • Pressure at one depth acts equally in all directions.
      • A liquid finds its own level.
      • Pressure depends on the density of the liquid.
    • Hydraulic principle; i.e. how to lift a car by taking the advatage of the fact that liquids are almost incompressable and therefore the pressure is transmitted in a liquid.
  • Atmospheric pressure:
    • demonstrations that show the existance of atmospheric pressure.
    • Ways to measure atmospehric pressure - basic working principles/ideas and names of some of the equipment.
    • Special attention: U-tube manometer and mercury barometer
      • Pressure is proportional to the difference of liquid levels in a tube. Take into account if the manometer is open or closed ended.
  • Floating, sinking and flying:
    • Fluid = liquid or gas
    • Archimedes'principle: Upthrust on an object is equal to the weight of the fluid replaced (F=dVg; d= density of fluid, V=how much fluid is displaced, i.e. is the object completely of partially submerged in the fluid.).
    • An object floats when it displaces its own weight of fluid.
    • This means that If the object is completely submerged in the fluid it will:
      • sink in the fluid if the density of the object is more than the denisty of the fluid.
      • float (not going downwards nor upwards) if the density of the object is the same as the density of the fluid.
      • float upwards in the fluid if the density of the object is less than the density of the fluid.
    • If the object is partially submerged in the fluid, i.e. it floats so that a part of it is above the fluid then:
      • weight of the whole object = weight of the fluid displaced
  • Fluid flow (Only the very basics is needed!)
    • Viscosity = "how easily fuids flow"
    • Fluids flow slowest next to the surface that surrounds the fluid (pipe walls, river banks,...)
    • Viscosity of fluids decreases as the temperature increases (Syrup flows faster when heated!).
    • Streamlining objects help them to move through fluids with minimum turbulence (Formula 1 cars, dolphins, ...)
    • Terminal velocity (skydivers jumping of the plane).
    • Bernoulli's principle: when fluids move faster then the pressure decreases. Think about everyday appications that use this principle. You see below some videos that help you to understand this principle.

PRESSURE VIDEOS