1 LIFE IN A FLUID. 2 http://www.physics.usyd.edu.au/teach_res/jp/fluids/wfluids.htm web notes: lect1.ppt density.pdf pressure1.pdf pressure2.pdf pressure3.pdf.

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1 LIFE IN A FLUID Slide 2 2 http://www.physics.usyd.edu.au/teach_res/jp/fluids/wfluids.htm web notes: lect1.ppt density.pdf pressure1.pdf pressure2.pdf pressure3.pdf Slide 3 3 Dr Manjula Sharma Lectures Tutorials Labs Assignments Exam Textbook Worked examples Slide 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 Slide 5 5 LEARNING AND DOING PHYSICS Physical quantities Symbols Units Typical values Relationships Principles Laws Mathematics Equations Graphs Appreciation Deep understanding Slide 6 6 ? Slide 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 = 10 -6 m 3 1 g = 10 -3 kg 1 g.mL -1 = 10 3 kg.m -3 Slide 8 8 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 SaltWater1024 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 9 9 and all the king's horses What force is required to separate the hemispheres? Is this force significant? ? Slide 10 10 Pressure P Is this pressure? What pressure is applied to the ground if a person stood on one heel? Slide 11 11 Pressure P Units pressure pPapascal1 Pa = 1 N.m -2 force FNnewton1 N = 1 kg.m.s -2 area Am 2 Slide 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 Earths surface due to weight of atmosphere air = 1.21 kg.m -3 g = 9.8 m.s -2 h ~ 10 km Slide 13 13 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 14 14 ? What does it mean when we are told to inflate a tyre to 100 kPa? Slide 15 15 Slide 16 16 ? How does a gas or liquid exert a pressure on its container walls? Slide 17 17 Slide 18 18 Slide 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 ~ Slide 20 20 F = ? N Slide 21 21 m = 70 kg F G = 700 N A = 10 mm x 10 mm A = (100)(10 -3 )(10 -3 ) m 2 A = 10 -4 m 2 p = F / A p = 700 / 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 22 22 Why is it better is use a sharp knife? Slide 23 23 FLUID PRESSURE p Slide 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 Slide 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? Slide 26 26 Pressure increases with depth in a fluid Slide 27 27 Slide 28 28 Slide 29 29 Slide 30 30 200 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 Slide 31 31 A scuba diver's lungs can rupture if he doesn't breathe while surfacing? Why? Slide 32 32 You dive deep down into the water. Does it matter whether it is in the ocean or a swimming pool? Slide 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.