# 1 LIFE IN A FLUID. 2 http://www.physics.usyd.edu.au/teach_res/jp/fluids09.

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<ul><li>Slide 1</li></ul> <p>1 LIFE IN A FLUID Slide 2 2 http://www.physics.usyd.edu.au/teach_res/jp/fluids09 Slide 3 3 Ian Cooper Lectures Tutorials Labs Duty Tutor Assignments Exam Textbook Worked examples Slide 4 4 Slide 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 = 10 -6 m 3 1 g = 10 -3 kg 1 g.mL -1 = 10 3 kg.m -3 Slide 6 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 Slide 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? Slide 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? Slide 9 9 Pressure P Units pressure pPapascal1 Pa = 1 N.m -2 force FNnewton1 N = 1 kg.m.s -2 area Am 2 Slide 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 Earths surface due to weight of atmosphere air = 1.21 kg.m -3 g = 9.8 m.s -2 h ~ 10 km Slide 11 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 Slide 12 12 ? What does it mean when we are told to inflate a tyre to 100 kPa? Slide 13 13 Slide 14 14 ? How does a gas or liquid exert a pressure on its container walls? Slide 15 15 Slide 16 16 Slide 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 ~ Slide 18 18 F = ? N Slide 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 = 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 Slide 20 20 Why is it better is use a sharp knife? Slide 21 21 FLUID PRESSURE p Slide 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 Slide 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? Slide 24 24 Pressure increases with depth in a fluid Slide 25 25 Slide 26 26 Slide 27 27 Slide 28 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 &gt; 200 mm p too large, lungs collapse Slide 29 29 A scuba diver's lungs can rupture if he doesn't breathe while surfacing? Why? Slide 30 30 You dive deep down into the water. Does it matter whether it is in the ocean or a swimming pool? Slide 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. </p>