Http://www.physics.usyd.edu.au/teach_res/jp/fluids/wfluids.htm http://www.physics.usyd.edu.au/teach_res/jp/fluids/ web notes: lect2.ppt pressure3.pdf pascal.pdf.

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http://www.physics.usyd.edu.au/teach_res/jp/fluids/wfluids.htm http://www.physics.usyd.edu.au/teach_res/jp/fluids/ web notes: lect2.ppt pressure3.pdf pascal.pdf Slide 2 Can you crush a steel can by pumping the air from the inside? Slide 3 Solution Setup Force to collapse can F = p A Assume atmospheric pressure acts only on outside surface of can p = p atm = 1.013 10 5 Pa Need to know outside surface area A of can need to know dimension of can. Consider a cylinder of radius R = 0.15 m and height h = 0.30 m A = 2( R 2 ) + 2 R h Action F = (1.013 10 5 ){(2 )(0.15) 2 + (2 )(0.15)(0.30)} N F = 4.3 10 5 N How big is this force? Consider a 70 kg person weight = 700 N force equivalent to the weight of > 61 people. Slide 4 How do we breath get the air in and out of our lungs? http://www.lung.ca/children/grades4_6/respiratory/how_we_breathe.html Slide 5 How do we breath? Gas pressure p = N k T / V = n R T / V Boltzmann constant k = 1.38x10 -23 J.K -1 Universal gas constant R = 8.314 J.mol -1.K -1 k = R / N A R = k N A Avogadro's constant N A = 6.023x10 23 mol -1 Gas laws (fixed quantity of gas) Boyle's Law (constant temperature) p = constant / V Charles Law (constant pressure) V = constant T (constant volume) p = constant T Slide 6 Slide 7 Slide 8 How can you measure the pressure of a gas? Slide 9 A D C B h Manometer measures gauge pressure g h Slide 10 What is a simple way to measure atmospheric pressure? Slide 11 h p atm B A C What is a simple way to measure atmospheric pressure? Mercury Barometer Slide 12 How do you measure blood pressure? p = g h Slide 13 Why does a brain tumor affect the signal cord? Slide 14 Slide 15 Pascal's Principle 1653 Blaise Pascal (1623 1662) Pressure applied to an enclosed fluid is transmitted undiminished to every portion of the fluid and walls of the containing vessel. Slide 16 Slide 17 Tennis Ball Impact on Eye A blow to the eye by a tennis ball can cause more damage than one might expect because of the transmission of the pressure to the back of the eye http://hyperphysics.phy-astr.gsu.edu/hbase/pasc2.html Slide 18 Hydraulic brakes http://hyperphysics.phy-astr.gsu.edu/hbase/pasc2.html Slide 19 How can a person easily lift a car? Slide 20 h2h2 h1h1 F1F1 F2F2 A1A1 A2A2 oil Slide 21 p = F / A W = F x p 1 = p 2 F 1 / A 1 = F 2 / A 2 F 2 = (A 2 / A 1 ) F 1 A 2 >> A 1 F 1 > A 1 h 1 >> h 2

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