Section 2 review
A fluid is a form of matter that easily flows and changes shape in response to an applied force. Forces in fluids (gases and liquids) act through pressure. Pressure is force per unit area and has units of pascals (N/m2) and pounds per square inch (psi or lbs/in2). Weight creates hydrostatic pressure, including atmospheric pressure and pressure underwater. Energy conservation along a streamline leads to Bernoulli’s equation, which relates pressure, volume, and height in a moving fluid. Read the text aloud
fluid, pressure, compressible, incompressible, Boyle’s law, Charles’s law, ideal gas, ideal gas law, density, Bernoulli’s equation, streamline

P= F A
PV=N k B T
ρ= m V
ρgh+ 1 2 ρ v 2 +P=constant

Review problems and questions

  1. A cubic box contains gas at a gauge pressure of 400,000 N/m2 (400,000 Pa) and measures 0.5 m × 0.5 m × 0.5 m. What force does the gas inside the box exert on any single side of the box? Read the text aloud Show
  1. Put the following pressures in order from lowest to highest.
    1. 1 atmosphere
    2. 1 psi
    3. 1 N/m2
    4. 100 psi
    5. 10,000 Pa Read the text aloud Show
  1. A submarine must be able to dive to a depth of 800 m. What is the absolute pressure at this depth? How does this compare to atmospheric pressure of 14.7 psi? Read the text aloud Show
  1. A cylindrical container full of liquid mercury is 80 cm high and has a radius of 10 cm. The density of mercury is 13,580 kg/m3.
    1. What is the volume of the container?
    2. What is the mass of the mercury?
    3. What pressure does the container exert on the floor? Assume that the mass of the container is negligibly small compared to the mass of the mercury. Read the text aloud Show
  1. Calculate the net force on a 3 m square window when a wind outside blows parallel to the window at 20 m/s. Assume that the quantity ρgh + ½ρv2 + P is the same inside and outside but that a sudden wind gust allows the outside pressure to drop compared to the inside pressure where v = 0. Express your answer in newtons and pounds. Do you think this is a significant problem for building engineers? Why? (Assume the density of air to be 1.29 kg/m3.) Read the text aloud Show
  1. A certain quantity of gas has an absolute pressure of 250,000 Pa at 20ºC. What would the pressure be if the temperature increased to 1,000ºC while the volume remained constant? Read the text aloud Show

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