Fluids (part 3)
Pressure in a fluid at depth
<?xml version="1.0" encoding="UTF-8"?>
<!--Mon Jan 16 2012 14:11:40 GMT-0500 (EST)-->
<XholonWorkbook>
<Notes>
Khan Academy
------------
Title: Fluids (part 3)
Description: Pressure in a fluid at depth
Url: http://www.khanacademy.org/video/fluids--part-3?playlist=Physics
InternalName: fluids--part-3
YoutubeId: 5EWjlpc0S00
Keywords: physics, chemistry, density, pressure
My Notes
--------
Internal pressure within a liquid.
the deeper you go into the ocean, the higher the pressure
imagine a cylinder filled with water, on a planet with no air
same gravity as Earth
thin piece of foil floating in middle of the cylinder, covering entire cross-section
to allow us to see the fluid moving
initially the fluid is static, with no net forces (F) acting on it
Fup = Fdown on the foil
Fdown = mass of liquid * g
density (rho) = mass / volume (kg/m^3)
mass of liquid = density * volume
Fdown = density * volume * g ?
volume = cross-sectional area of cylinder (A) * height of liquid above the cylinder (h)
Fdown = density * h * A * g ? (I think this is the pressure down)
What is the pressure on the foil?
downward pressure = Fdown / A = density * h * g
example
density of water = 1000 kg / m^3 (on Earth ?)
h = 10 m
pressure = 1000 * 10 * 9.8 = 98000 Pa
</Notes>
<script implName="lang:python:inline:"><![CDATA[
print "height = 12.34 m"
]]></script>
<script implName="lang:javascript:inline:"><![CDATA[
print("height = 56.78 meters\n");
]]></script>
<_-.XholonClass>
<!-- domain objects -->
<PhysicalSystem/>
<Cylinder/>
<Liquid/>
<Foil/>
<!-- quantities -->
<Height superClass="Length"/> <!-- height of liquid above the foil -->
</_-.XholonClass>
<xholonClassDetails>
<Foil>
<port name="area" connector="#xpointer(../Area)"/>
<port name="mass" connector="#xpointer(../Liquid/Mass)"/>
<port name="height" connector="#xpointer(../Liquid/Height)"/>
<port name="volume" connector="#xpointer(../Liquid/Volume)"/>
<port name="density" connector="#xpointer(../Liquid/Density)"/>
<port name="pressure" connector="#xpointer(Pressure)"/>
<port name="g" connector="#xpointer(../../AccelerationDueToGravity)"/>
</Foil>
</xholonClassDetails>
<PhysicalSystem>
<Cylinder>
<Area>1.0 m^2</Area> <!-- cross-sectional area -->
<Liquid roleName="above">
<Mass>1000.0 kg</Mass> <!-- the mass of a cubic meter of water -->
<Height>10.0 m</Height>
<Volume>0.0 m^3</Volume>
<Density>0.0 kg/m^3</Density>
</Liquid>
<Foil>
<Pressure>0.0 Pa</Pressure>
</Foil>
<Liquid roleName="below">
<!-- height is unknown -->
</Liquid>
</Cylinder>
<AccelerationDueToGravity/> <!-- 9.80665 m/s² -->
</PhysicalSystem>
<Blockbehavior implName="lang:python:inline:"><![CDATA[
# TODO
]]></Blockbehavior>
<Foilbehavior implName="lang:javascript:inline:"><![CDATA[
// The foil will do all the calculations. It needs to determine the pressure on it.
volume.setVal(area.val * height.val);
density.setVal((mass.val * height.val) / volume.val);
pressure.setVal(density.val * height.val * g.val);
// result: 98066.5 Pa, Sal gets 98000 Pa
]]></Foilbehavior>
<Blockbehavior implName="lang:bsh:inline:"><![CDATA[
// This works if pasted in as a last child of Block.
//height.incVal(0.02);
//System.out.print("Java/Beanshell wants something to do. Height:" + height + "\n");
]]></Blockbehavior>
<Blockbehavior implName="lang:jruby:inline:"><![CDATA[
#require 'java'
# This works if pasted in as a last child of Block.
#$height.incVal(0.02)
#puts "Ruby wants something to do. Height: #{$height}"
]]></Blockbehavior>
<Blockbehavior implName="lang:groovy:inline:"><![CDATA[
// This works if pasted in as a last child of Block.
//height.incVal(0.02);
//System.out.print("Groovy wants something to do. Height:" + height + "\n");
]]></Blockbehavior>
</XholonWorkbook>