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
3 Dr Manjula Sharma Lectures Tutorials Labs Assignments Exam Textbook Worked examples
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 LEARNING AND DOING PHYSICS Physical quantities Symbols Units Typical values Relationships Principles Laws Mathematics Equations Graphs Appreciation Deep understanding
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
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
9 … and all the king's horses … What force is required to separate the hemispheres? Is this force significant? ?
10 Pressure P Is this pressure? What pressure is applied to the ground if a person stood on one heel?
11 Pressure P Units pressure pPapascal1 Pa = 1 N.m -2 force FNnewton1 N = 1 kg.m.s -2 area Am 2
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
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
31 A scuba diver's lungs can rupture if he doesn't breathe while surfacing? Why?
32 You dive deep down into the water. Does it matter whether it is in the ocean or a swimming pool?
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.