Fluids day 1
Transcript of Fluids day 1
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Fluid Mechanics and Thermodynamics
Day 1: Object Density and Hydrostatic Pressure
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Fluids are anything that can flow: liquids or gases.
Fluids conform to their containers
What is a fluid?
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What if I had a piece of material like the cylinder shown, and I wanted to know what material it was?
Brainstorm… What methods could you use to determine if they were the same?
What if?
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What am I?
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Density: Ratio of mass to volume of an object
To calculate density, determine the mass per unit volume, or:
r =m/v
Density (kg/m3) is an intrinsic property of matter.
Specific gravity: The ratio of an objects density to that of water at 4°C
Things to know:
What is the specific gravity of Aluminum? What about oil?
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Pressure is force/area
In pascals (Pa) = N/m2
Example: A cat with mass 20 kg walks across the snow. If snow collapses under a pressure of 0.5 psi (2500 Pa), determine the minimum size of the cat’s paws.
Pressure
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Does AIR have pressure?
How do you know?
What about WATER?
1 atmosphere = 101.325 kPa , or about 101,300 Pa.
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My fish tank is 10 gallons. (I googled: 10 gallons = 0.0379 m3)
How much pressure does the top (open) surface of my tank experience?
How about the bottom?
*Note that we’re only interested in the pressure downwards on the floor of the tank. The sides cancel out!
How much pressure?
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The pressure at any depth is the sum of the weight of the fluid and
the atmosphere:
P = P0+ρgh
ρ = fluid’s density, g = 9.8 m/s2, and h = height of water column/ depth
Absolute Pressure and Gauge Pressure
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A foolish boy tries to use a garden hose for air as he swims at the bottom of a 5.00 m deep pool. What goes wrong?
Absolute Pressure and Gauge Pressure
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Think?
How does the pressure 6” below the surface of a swimming pool at sea level compare to the pressure 6” below the ocean?
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Use a blood pressure cuff (sphygmomanometer) to measure the maximum and minimum pressure exerted by your heart.
Restrict blood, then release until the very first push: systolic: heart generates its maximum pressure.
Keep relieving pressure (letting out air) until blood flows continuously: part of hearbeat cycle when pressure is lowest: Diastolic.
120/80 is typical…
Blood Pressure?
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Chapter 14: Read 14.1-14.7 Do #3.1, 4.1, and 6.2
HW: Due Friday