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physicsyd.au/teach_res/jp/fluids09

Lecture 2. http://www.physics.usyd.edu.au/teach_res/jp/fluids09. Can you crush a steel can by pumping the air from the inside?. Explain. 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

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physicsyd.au/teach_res/jp/fluids09

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

  2. Can you crush a steel can by pumping the air from the inside? Explain

  3. Solution Setup Force to collapse can F = p A Assume atmospheric pressure acts only on outside surface of can p = patm = 1.013105 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(R2) + 2R h Action F = (1.013105){(2)(0.15)2 + (2)(0.15)(0.30)} N F = 4.3105 N How big is this force? Consider a 70 kg person  weight = 700 N  force equivalent to the weight of > 61 people.

  4. How do we breath – get the air in and out of our lungs? p V = n R T http://www.lung.ca/children/grades4_6/respiratory/how_we_breathe.html

  5. How do we breath?

  6. How can you measure the pressure of a gas?

  7. D h A C B How can you measure the pressure of a gas? Manometer measures gauge pressure g h

  8. What is a simple way to measure atmospheric pressure?

  9. What is a simple way to measure atmospheric pressure? A Mercury Barometer h patm patm B C r

  10. How do you measure blood pressure? p = r g h

  11. Why does a brain tumor affect the signal cord?

  12. Why does a brain tumor affect the signal cord?

  13. 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.

  14. 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

  15. Hydraulic brakes http://hyperphysics.phy-astr.gsu.edu/hbase/pasc2.html

  16. How can a person easily lift a car?

  17. F2 F1 h1 oil h2 A1 A2

  18. p1 = p2 F1 / A1 = F2 / A2 F2 = (A2 / A1) F1 A2 >> A1 F1 << F2 W1 = W2 F1 h1 = F2 h2 F1 h1 = (A2 / A1) F1 h1 h1 = (A2 / A1) h2 A2 >> A1 h1 >> h2 p = F / A W = F x

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