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PHY 113 C General Physics I 11 AM - 12:15 P M TR Olin 101 Plan for Lecture 20:

PHY 113 C General Physics I 11 AM - 12:15 P M TR Olin 101 Plan for Lecture 20: Chapter 19: The notion of temperature Review of fluid physics Temperature equilibrium Temperature scales Temperature in ideal gases. Review: . The physics of fluids.

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PHY 113 C General Physics I 11 AM - 12:15 P M TR Olin 101 Plan for Lecture 20:

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  1. PHY 113 C General Physics I 11 AM - 12:15 PM TR Olin 101 Plan for Lecture 20: Chapter 19: The notion of temperature Review of fluid physics Temperature equilibrium Temperature scales Temperature in ideal gases PHY 113 C Fall 2013 -- Lecture 20

  2. PHY 113 C Fall 2013 -- Lecture 20

  3. Review: • The physics of fluids. • Fluids include liquids (usually “incompressible) and gases (highly “compressible”). • Fluids obey Newton’s equations of motion, but because they move within their containers, the application of Newton’s laws to fluids introduces some new forms. • Pressure: P=force/area • 1 (N/m2) = 1 Pascal • Density: r =mass/volume 1 kg/m3 = 0.001 gm/ml PHY 113 C Fall 2013 -- Lecture 20

  4. Review of equations describing static fluids in terms of pressure P and density r: Note that for compressible fluids (such as air), the relationship between pressure and density is more complicated. Buoyant force for fluid acting on a solid – net force due to volume Vdisplaced being displaced in fluid: FB=rfluidVdisplacedg PHY 113 C Fall 2013 -- Lecture 20

  5. Bernoulli’s equation: PHY 113 C Fall 2013 -- Lecture 20

  6. Webassign questions on fluids (Assignment #17) A large man sits on a four-legged chair with his feet off the floor. The combined mass of the man and chair is 95.0 kg. If the chair legs are circular and have a radius of 0.500 cm at the bottom, what pressure does each leg exert on the floor? mg/4 mg P=F/A=(mg/4)/A PHY 113 C Fall 2013 -- Lecture 20

  7. Webassign questions on fluids (Assignment #17) A swimming pool has dimensions 32.0 m ✕ 7.0 m and a flat bottom. The pool is filled to a depth of 2.50 m with fresh water. (a) What is the force exerted by the water on the bottom?(b) What is the force exerted by the water on each end? (The ends are 7.0 m.)(c) What is the force exerted by the water on each side? (The sides are 32.0 m.) PHY 113 C Fall 2013 -- Lecture 20

  8. Webassign questions on fluids (Assignment #17) A swimming pool has dimensions 32.0 m ✕ 7.0 m and a flat bottom. The pool is filled to a depth of 2.50 m with fresh water. (a) What is the force exerted by the water on the bottom? h=2.5m Fbottom=PA=rghA PHY 113 C Fall 2013 -- Lecture 20

  9. Webassign questions on fluids (Assignment #17) A swimming pool has dimensions 32.0 m ✕ 7.0 m and a flat bottom. The pool is filled to a depth of 2.50 m with fresh water. (b) What is the force exerted by the water on each end? (The ends are 7.0 m.) h=2.5m w=7.0m PHY 113 C Fall 2013 -- Lecture 20

  10. Webassign questions on fluids (Assignment #17) PHY 113 C Fall 2013 -- Lecture 20

  11. Dy Dz PHY 113 C Fall 2013 -- Lecture 20

  12. PHY 113 C Fall 2013 -- Lecture 20

  13. Webassign questions on fluids (Assignment #17) The gravitational force exerted on a solid object is 5.30 N. When the object is suspended from a spring scale and submerged in water, the scale reads 3.50 N (figure). Find the density of the object. PHY 113 C Fall 2013 -- Lecture 20

  14. Webassign questions on fluids (Assignment #17) A light balloon is filled with 373 m3 of helium at atmospheric pressure. (a) At 0°C, the balloon can lift a payload of what mass? Note: rair = 2.9 kg/m3: rHe= 0.179 kg/m3 PHY 113 C Fall 2013 -- Lecture 20

  15. Webassign questions on fluids (Assignment #17) A hypodermic syringe contains a medicine with the density of water (see figure below). The barrel of the syringe has a cross-sectional area A = 2.40  10-5 m2, and the needle has a cross-sectional area a = 1.00  10-8 m2. In the absence of a force on the plunger, the pressure everywhere is 1.00 atm. A force  of magnitude 2.65 N acts on the plunger, making medicine squirt horizontally from the needle. Determine the speed of the medicine as it leaves the needle's tip.  PHY 113 C Fall 2013 -- Lecture 20

  16. Temperature Dictionary definition: temperature – a measure of the the warmth or coldness of an object or substance with reference to some standard value. The temperature of two systems is the same when the systems are in thermal equilibrium. “Zeroth” law of thermodynamics: If objects A and B are separately in thermal equilibrium with a third object C, then objects A and B are in thermal equilibrium with each other. Not equilibrium: Equilibrium: T1 T2 T3 PHY 113 C Fall 2013 -- Lecture 20

  17. Constant temperature “bath” At equilibrium: T T PHY 113 C Fall 2013 -- Lecture 20

  18. Temperature scales TF=9/5 TC + 32 Kelvin scale: T = TC + 273.15o T  0 PHY 113 C Fall 2013 -- Lecture 20

  19. iclicker question: • Suppose you find yourself in a hotel in Europe or Canada. Which Celsius temperature would you set the thermostat for comfort? • -20oC • +20oC • +40oC • +60oC • +80oC PHY 113 C Fall 2013 -- Lecture 20

  20. There is a lowest temperature: T0 = -273.15o C = 0 K Kelvin (“absolute temperature”) scale TC = -273.15 + TK Example – Room temperature = 68o F = 20o C = 293.15 K PHY 113 C Fall 2013 -- Lecture 20

  21. PHY 113 C Fall 2013 -- Lecture 20

  22. Thermal exansion: DL = a LiDT DL Effects of temperature on matter Solids and liquids Model of a solid composed of atoms and bonds Li (equilibrium bond length at Ti) PHY 113 C Fall 2013 -- Lecture 20

  23. Typical expansion coefficients at TC = 20o C: Linear expansion: DL = a LiDT Steel: a = 11 x 10-6/ oC Concrete: a = 12 x 10-6/ oC Volume expansion: V=L3  DV = 3a ViDT = b ViDT Alcohol: b = 1.12 x 10-4/ oC Air: b = 3.41 x 10-3/ oC PHY 113 C Fall 2013 -- Lecture 20

  24. iclicker question • On the last slide – we suggest that b=3a. Is this result • One of those mysteries of physics that has no explanation? • A result that we can derive?  L L+DL V=L3 V+DV=(L+DL)3@V(1+3(DL/L)) PHY 113 C Fall 2013 -- Lecture 20

  25. PHY 113 C Fall 2013 -- Lecture 20

  26. Brass Steel PHY 113 C Fall 2013 -- Lecture 20

  27. Switch in thermostat Modern thermostats use electrical circuits to detect temperature PHY 113 C Fall 2013 -- Lecture 20

  28. Effects of temperature on materials – continued strange case of water: PHY 113 C Fall 2013 -- Lecture 20

  29. Effects of temperature on materials – continued -- ideal gas “law” (thanks to Robert Boyle (1627-1691), Jacques Charles (1746-1823), and Gay-Lussac (1778-1850) 8.314 J/(mol K) temperature in K volume in m3 # of moles pressure in Pascals 1 mole corresponds to 6.022 x 1023 molecules PHY 113 C Fall 2013 -- Lecture 20

  30. P0 =12.6 atm T0 =27.5oC n0 P=? T=81.0oC n=n0/3 PHY 113 C Fall 2013 -- Lecture 20

  31. Assuming that air behaves like an ideal gas, what is the density of air at T=0o C and P=1 atm? PHY 113 C Fall 2013 -- Lecture 20

  32. Typical composition of air: url: http://www.engineeringtoolbox.com/molecular-mass-air-d_679.html PHY 113 C Fall 2013 -- Lecture 20

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