# Fluid Fluid - any substance that “flows”… liquids and gases.

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Fluid Fluid - any substance that “flows”… liquids and gases.
Ex. Water and Air

Fluid Pressure 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.

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

Calculate Fluid Pressure
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.

Properties of 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.

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!

Calculate Buoyant Force
Weight Difference method ~ Fb= Dry weight – Wet weight Weight of displaced water ~ Fb= ρ · g · v

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.

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