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1 LIFE IN A FLUID. 2 web notes: lect1.ppt density.pdf pressure1.pdf pressure2.pdf pressure3.pdf.

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Presentation on theme: "1 LIFE IN A FLUID. 2 web notes: lect1.ppt density.pdf pressure1.pdf pressure2.pdf pressure3.pdf."— Presentation transcript:

1 1 LIFE IN A FLUID

2 2 web notes: lect1.ppt density.pdf pressure1.pdf pressure2.pdf pressure3.pdf

3 3 Dr Manjula Sharma Lectures Tutorials Labs Assignments Exam Textbook Worked examples

4 4 Identify  Setup  Execute  Evaluate IDENTIFY Identify what the question asking Identify the known and unknown physical quantities (units) SETUP Visualise the physical situation Diagrams - reference frames / coordination system / origin / directions Write down key concepts, principles, equations, assumptions that may be needed to answer the question EXECUTE Answer to the question from what you know. Numerical questions - solve before calculations - manipulate equations then substitute numbers add comments. EVALUATE CHECK - answer reasonable, assumptions, units, signs, significant figures, look at limiting cases

5 5 LEARNING AND DOING PHYSICS Physical quantities Symbols Units Typical values Relationships Principles Laws Mathematics Equations Graphs Appreciation Deep understanding

6 6 ?

7 7 Definition (  Greek letter rho )  density of object m mass of object V volume of object Units SI unit kg.m -3 Other unitsg.mL -1 1 mL = 1 cm 3 = (10 -2 ) 3 m 3 = m 3 1 g = kg 1 g.mL -1 = 10 3 kg.m -3

8 8 Density values (kg.m -3 ) Interstellar space Best laboratory vacuum Air (20 °C and 1 atm) 1.21 Styrofoam 100 Ice 917 Water (20 °C and 1 atm) 998 SaltWater1024 Whole blood1060 Earth (average)~5500 Iron7900 Mercury Osmium (most dense found on earth) Uranium nucleus Neutron star (core) 10 18

9 9 … and all the king's horses … What force is required to separate the hemispheres? Is this force significant? ?

10 10 Pressure P Is this pressure? What pressure is applied to the ground if a person stood on one heel?

11 11 Pressure P Units pressure pPapascal1 Pa = 1 N.m -2 force FNnewton1 N = 1 kg.m.s -2 area Am 2

12 12 How large is atmospheric pressure? Rough calculation p = F / A p = m g / A p =  V g / A p =  A h g / A p =  h g p = (1)(10 4 )(10) Pa p = 10 5 Pa Pressure at Earth’s surface due to weight of atmosphere  air = 1.21 kg.m -3 g = 9.8 m.s -2 h ~ 10 km

13 13 Atmospheric Pressure p atm 1.013x10 5 Pa kPa 1013 hPa (hecto) 1013 mb (millibar) b (bar) 760 mmHg 14.7 lb.in 2 (14.7 psi) mH 2 0

14 14 ? What does it mean when we are told to inflate a tyre to 100 kPa?

15 15

16 16 ? How does a gas or liquid exert a pressure on its container walls?

17 17

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19 19 p atm = 1x10 5 Pa R = ??? m A = 2  R 2 p = F / A F = p A F = (1x10 5 )(2  )( ) 2 N F = ??? N 70 kg person HOW MANY PEOPLE? N = F / F person ~

20 20 F = ? N

21 21 m = 70 kg F G = 700 N A = 10 mm x 10 mm A = (100)(10 -3 )(10 -3 ) m 2 A = m 2 p = F / A p = 700 / Pa p = 700 x 10 4 Pa p = 7 x 10 6 Pa p / p atm = 7x10 6 / 1x10 5 atm = 70 atm

22 22 Why is it better is use a sharp knife?

23 23 FLUID PRESSURE p

24 24 parallel to the surface and the interaction is not simply described by the pressure. Pressure has no intrinsic direction of its own (pressure is a scalar). t t

25 25 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?

26 26 Pressure increases with depth in a fluid

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30 mm p h = p atm +  g h  p = p h – p atm  p =  g h  p = (1030)(9.8)(0.2) Pa  p = 2x10 3 Pa if h > 200 mm  p too large, lungs collapse

31 31 A scuba diver's lungs can rupture if he doesn't breathe while surfacing? Why?

32 32 You dive deep down into the water. Does it matter whether it is in the ocean or a swimming pool?

33 33 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.


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