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Fluid Mechanics

Fluid Mechanics. Newtonian Fluids. Gases are considered compressible fluids Liquids are considered incompressible fluids Another thing we pretend is true because the compression is usually a negligible amount Non-Newtonian fluids do not always act predictably. Pascal's Principles.

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Fluid Mechanics

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  1. Fluid Mechanics

  2. Newtonian Fluids • Gases are considered compressible fluids • Liquids are considered incompressible fluids • Another thing we pretend is true because the compression is usually a negligible amount • Non-Newtonian fluids do not always act predictably

  3. Pascal's Principles • External pressure applied to a fluid will be applied uniformly throughout the fluid F₁/A₁ = F₂/A₂

  4. F₁/A₁ = F₂/A₂ • 50 Newtons is applied to pump a squirt gun with a cylinder surface area of .01 square meters. How much force does it take to plug the barrel of the squirt gun if the area of the opening is 0.001 square meters?

  5. Does this obey the law of conservation of energy?Explain your answer!

  6. Static Pressure and Depth • F=mg and the mass = ρV • ρ = density • V=area of the cross section x height • So F=ρgV= ρgAh P = F/A= ρgh *for a uniform shape

  7. Explain this phenomenon:

  8. Relating KE, GPE, and existing P • From conservation of energy we can derive Bernoulli’s equation: P₁ + ρgh₁ + 1/2ρv₁² = P₂ + ρgh₂ + 1/2ρv₂²

  9. Vocabulary • Conditions • Isobaric – constant pressure • Isothermic – constant temperature • Adiabatic – no heat is added or removed from the system; this is an important distinction from isothermic • Laminar Flow – smooth movement of fluid without turbulence (this is an important assumption of Bernoulli’s equation) • Turbulent Flow – irregular movement of fluid where the fluid may be working against parts of its own movement

  10. Assumptions about an “ideal gas” • The gas is composed of many molecules that are relativelyfar apart • As a whole the molecules act according to the laws of motion but individually their motion is random • Molecules undergo elastic collisions • Forces between molecules have no effect except during a collision • The gas is a pure substance • The gas and the walls of the container are not exchanging thermal energy

  11. Ideal Gas Law • P₁V₁/T ₁ = P₂V₂/T ₂ or • PV=nRT • Pressure x Volume = number of Moles of the substance x Universal Gas Constant x Temperature in Kelvin 0⁰ Kelvin = -273⁰ Celsius Pressure is in Pascals (Pa) or Nm² (1 Pa= 1 Nm²) R= 8.31 joules per mole kelvin

  12. Relating P₁V₁/T ₁ = P₂V₂/T ₂ to your experiences: • What happens when you heat up a closed container? • What happens to temperature when you decrease the pressure in a spray can? • How might an air conditioner work? • Does opening the refrigerator door cool off the kitchen?

  13. How does the steamboat toy work? • What does an increase in temperature do to the pressure? • How is pressure related to force?

  14. Example of Algebraic Sponsor m₁a₁ = m₂a₂ The mass of the boat is accelerated according to Newton’s third law. The force created by the pressure in the steam chamber results in equal and opposite forces acting on the boat and the water. Rudder Madness m₁a₁ = -m₂a₂

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