# 1 LIFE IN A FLUID. 2

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

1 LIFE IN A FLUID

2 http://www.physics.usyd.edu.au/teach_res/jp/fluids09

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

4

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 = 10 -6 m 3 1 g = 10 -3 kg 1 g.mL -1 = 10 3 kg.m -3

6 Density values (kg.m -3 ) Interstellar space10 -20 Best laboratory vacuum10 -17 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 Mercury13 600 Osmium (most dense found on earth) 22 500 Uranium nucleus 10 17 Neutron star (core) 10 18

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

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 Atmospheric Pressure p atm 1.013x10 5 Pa 101.3 kPa 1013 hPa (hecto) 1013 mb (millibar) 1.013 b (bar) 760 mmHg 14.7 lb.in 2 (14.7 psi) 10.34 mH 2 0

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

13

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

15

16

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 F = ? N

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 = 10 -4 m 2 p = F / A p = (9700 / 10 -4 ) Pa p = 700 x 10 4 Pa p = 7 x 10 6 Pa p / p atm = 7x10 6 / 1x10 5 atm = 70 atm

20 Why is it better is use a sharp knife?

21 FLUID PRESSURE p

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 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 Pressure increases with depth in a fluid

25

26

27

28 200 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 A scuba diver's lungs can rupture if he doesn't breathe while surfacing? Why?

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

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.