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1 LIFE IN A FLUID. 2

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Presentation on theme: "1 LIFE IN A FLUID. 2"— Presentation transcript:

1 1 LIFE IN A FLUID

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3 3 Ian Cooper Lectures Tutorials Labs Duty Tutor Assignments Exam Textbook Worked examples

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5 5 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

6 6 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 SaltWater 1024 Whole blood1060 Earth (average)~5500 Iron7900 Mercury Osmium (most dense found on earth) Uranium nucleus Neutron star (core) 10 18

7 7 … and all the king's horses … What force is required to separate the hemispheres? Is this force significant? ? What physical quantities do we need to consider?

8 8 Pressure P Is this pressure? What pressure is applied to the ground if a person stood on one heel? ? What physical quantities do we need to consider?

9 9 Pressure P Units pressure pPapascal1 Pa = 1 N.m -2 force FNnewton1 N = 1 kg.m.s -2 area Am 2

10 10 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

11 11 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

12 12 ? What does it mean when we are told to inflate a tyre to 100 kPa?

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14 14 ? How does a gas or liquid exert a pressure on its container walls?

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17 17 p atm = 1x10 5 Pa R = m A = 2  R 2 p = F / A F = p A F = (1x10 5 )(  )( ) 2 N F = x10 N 70 kg person HOW MANY PEOPLE? N = F / F person ~

18 18 F = ? N

19 19 m = 70 kg g = 10 m.s -2 F G = 700 N A = 10 mm x 10 mm A = (10x10 -3 )(10x10 -3 ) m 2 A = m 2 p = F / A p = (9700 / ) Pa p = 700 x 10 4 Pa p = 7 x 10 6 Pa p / p atm = 7x10 6 / 1x10 5 atm = 70 atm

20 20 Why is it better is use a sharp knife?

21 21 FLUID PRESSURE p

22 22 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

23 23 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?

24 24 Pressure increases with depth in a fluid

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28 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

29 29 A scuba diver's lungs can rupture if he doesn't breathe while surfacing? Why?

30 30 You dive deep down into the water. Does it matter whether it is in the ocean or a swimming pool?

31 31 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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