LIFE IN A FLUID

http://www.physics.usyd.edu.au/teach_res/jp/fluids/wfluids.htmweb notes: lect1.ppt

density.pdf pressure1.pdf pressure2.pdf pressure3.pdf

Dr Manjula Sharma

LecturesTutorialsLabsAssignmentsExamTextbookWorked examples

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

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

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

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?

Pressure PUnitspressure pPapascal1 Pa = 1 N.m-2force FNnewton1 N = 1 kg.m.s-2area Am2

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

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

?What does it mean when we are told to inflate a tyre to 100 kPa?

?How does a gas or liquid exert a pressure on its container walls?

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 ~

F = ? N

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

Why is it better is use a sharp knife?

FLUID PRESSURE p

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?

Pressure increases with depth in a fluid

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

A scuba diver's lungs can ruptureif he doesn't breathe while surfacing?

Why?

You dive deep down into the water.

Does it matter whether it is in the ocean or a swimming pool?

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.