fluid fluid - any substance that flows… liquids and gases. ex. water and air
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Fluid
• Fluid - any substance that “flows”… liquids and gases.
• Ex. Water and Air
• Pressure - force per unit of area.
• A force that exist in fluids are caused by the mass and motion of the particles making up the fluid.
Fluid PressureFluid Pressure
Calculate Fluid Pressure
• P = ρ · g · h Units: N/m2 or Pa
• Air pressure at sea level is 14.7 psi = 760 mm Hg = 101 kPa = 1 atm.
• ρ of H2O is 1000 kg/m3
• What is the pressure due to water 3.0 m below the surface of a lake?
• A truck falls through the “too thin” ice at Lake Poinsett, and sinks 7 m to the bottom.
– What is the pressure on the truck at this depth?
– If the area of one of the doors on the truck is 0.7 m2, calculate the force that the water exerts on it.
Calculate Fluid Pressure
Calculate Fluid Pressure
• Fluid pressure acts in all directions.
• Force of gravity causes the pressures in a fluid to vary with depth only. Not with horizontal position.
• Fluids will move from areas of high pressure to areas of low pressure.
Properties of PressureProperties of Pressure
Hydraulics• Pascal’s
Principle - pressure is transmitted equally throughout a confined liquid.
• Multiplies force!
• Ex. Brakes, hydraulic lifts, etc.
Calculate Hydraulics• P = F1 = F2
• The small piston of a hydraulic lift has a cross sectional area of 3 cm2, and the large piston has an area of 200 cm2. What force must be applied to the small piston to raise a load of 15,000 N?
A1 A2
Buoyancy
• The upward force exerted by a fluid on a substance partly or completely immersed in it.
• Fb< wt. of sub. SINK
• Fb ≥ wt. of sub. FLOAT!
• Weight Difference method~ Fb= Dry weight – Wet weight
• Weight of displaced water~ Fb= ρ · g · v
Calculate Buoyant ForceCalculate Buoyant Force
Archimedes Principle
• Archimedes Principle - The buoyant force acting in a substance in a fluid at rest is equal to the weight of the fluid displaced by the substance.
• Fb= weight of displaced fluid
or
Fb= ρ · g · v
Sink or Float?
• Density (object)> Density (fluid) SINKS
• Density (object) ≤ Density (fluid) FLOATS
Bernoulli’s Principle
• For a fluid undergoing steady flow, the pressure is lower where the fluid is flowing faster.
• Ex. Shower curtain, airplane wing, etc.