lect1
description
Transcript of lect1
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LIFE IN A FLUID
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http://www.physics.usyd.edu.au/teach_res/jp/fluids/wfluids.htmweb notes: lect1.ppt
density.pdf pressure1.pdf pressure2.pdf pressure3.pdf
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Dr Manjula Sharma
LecturesTutorialsLabsAssignmentsExamTextbookWorked examples
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Identify Setup Execute EvaluateIDENTIFYIdentify what the question askingIdentify the known and unknown physical quantities (units) SETUPVisualise the physical situation Diagrams - reference frames / coordination system / origin / directions Write down key concepts, principles, equations, assumptions that may be needed to answer the questionEXECUTEAnswer to the question from what you know. Numerical questions - solve before calculations - manipulate equations then substitute numbers add comments. EVALUATECHECK - answer reasonable, assumptions, units, signs, significant figures, look at limiting cases
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LEARNING AND DOING PHYSICSPhysical quantities Symbols Units Typical values
Relationships Principles Laws Mathematics Equations GraphsAppreciationDeep understanding
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UnitsSI unit kg.m-3Other unitsg.mL-11 mL = 1 cm3 = (10-2)3 m3 = 10-6 m3 1 g = 10-3 kg 1 g.mL-1 = 103 kg.m-3
Definition (r Greek letter rho)r density of object
m mass of objectV volume of object
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Density values (kg.m-3)Interstellar space10-20Best laboratory vacuum10-17Air (20 C and 1 atm)1.21Styrofoam 100Ice 917Water (20 C and 1 atm) 998SaltWater1024Whole blood1060Earth (average)~5500Iron7900Mercury13 600Osmium (most dense found on earth)22 500Uranium nucleus 1017Neutron star (core) 1018
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and all the king's horses
What force is required to separate the hemispheres? Is this force significant?
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Pressure PIs this pressure?
What pressure is applied to the ground if a person stood on one heel?
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Pressure PUnitspressure pPapascal1 Pa = 1 N.m-2force FNnewton1 N = 1 kg.m.s-2area Am2
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How large is atmospheric pressure?Rough calculation
p = F / A
p = m g / A
p = r V g / A
p = r A h g / A
p = r h g
p = (1)(104)(10) Pa
p = 105 PaPressure at Earths surface due to weight of atmosphere
rair = 1.21 kg.m-3
g = 9.8 m.s-2
h ~ 10 km
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Atmospheric Pressure patm
1.013x105 Pa101.3 kPa1013 hPa (hecto)1013 mb (millibar)1.013 b (bar)760 mmHg14.7 lb.in2 (14.7 psi)10.34 mH20
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?What does it mean when we are told to inflate a tyre to 100 kPa?
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?How does a gas or liquid exert a pressure on its container walls?
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patm = 1x105 Pa
R = m
A = 2p R2
p = F / A
F = p A
F = (1x105)(2p)( )2 N
F = 5.7x104 N70 kg person HOW MANY PEOPLE? N = F / Fperson ~
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F = ? N
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m = 70 kg
FG = 700 N
A = 10 mm x 10 mm
A = (100)(10-3)(10-3) m2
A = 10-4 m2
p = F / A
p = 700 / 10-4 Pa
p = 700 x 104 Pa
p = 7 x 106 Pa
p / patm = 7x106 / 1x105 atm = 70 atm
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Why is it better is use a sharp knife?
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FLUID PRESSURE p
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How long can your snorkel be?
Why do your ears feel different when you dive into deep water?
Why does atmospheric pressure change as you go up a mountain?
How does a barometer work?
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Pressure increases with depth in a fluid
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200 mmph = patm + r g h
Dp = ph patm
Dp = r g h
Dp = (1030)(9.8)(0.2) Pa
Dp = 2x103 Pa
if h > 200 mm Dp too large, lungs collapse
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A scuba diver's lungs can ruptureif he doesn't breathe while surfacing?
Why?
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You dive deep down into the water.
Does it matter whether it is in the ocean or a swimming pool?
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You dive deep down into the water. Does it matter whether it is in the ocean or a swimming pool?
!The pressure within a uniform stationary fluid is the same at all points in the same horizontal plane.