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Announcements 1/12/10

Announcements 1/12/10. Prayer Extra-credit lecture, “The Physics of Bicycles”, right after class today, 2 pm, 455 MARB. If you attend, turn in 1-page (max) summary to get extra credit points. I won’t have office hours today.

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Announcements 1/12/10

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  1. Announcements 1/12/10 • Prayer • Extra-credit lecture, “The Physics of Bicycles”, right after class today, 2 pm, 455 MARB. If you attend, turn in 1-page (max) summary to get extra credit points. • I won’t have office hours today. • For HW problem 4-9 (extra credit), you need the bulk modulus of copper. You should get that from Chapter 12 of your book (if you don’t have that chapter, there are some books available in the Tutorial Lab). • I’m not following books order for Chapters 20-22. Be sure to look at syllabus. • Don’t forget to turn in work for ALL homework problems • (1+x)n≈ 1 + nx

  2. Reading quiz (graded): • Which two temperature scales have the same sized intervals, varying only in their choice of the zero point? • Fahrenheit and Celsius • Fahrenheit and Kelvin • Kelvin and Celsius • Kelvin and BTU • Fahrenheit and Pentatonic

  3. Temperature • Temperature scales • What’s a thermometer?

  4. Demos: • Liquid bulb thermometer • Constant volume thermometer

  5. Thermal contact • Two objects in “thermal contact” will come to “thermal equilibrium”, and then have the same “temperature”. • What is thermal contact? • What is thermal equilibrium? • What is temperature? • Is there a maximum temperature? • Is there a minimum temperature?

  6. Thermal expansion • What went wrong here?

  7. Thermal Expansion • The equation: • a = “________________” For reference: asteel = 11  10-6 /C

  8. Videos/Demo: • Demo: Ring & Ball • Demo: Bimetallic strip • Video: Bimetallic strip

  9. Thought question (ungraded) • You heat a disc with a hole in it. Will the radius of the hole get larger, smaller, or stay the same? • Larger • Smaller • Stay the same

  10. Thought question (ungraded): • If the expansion of all of the linear dimensions of an object is proportional to ΔT, what should the expansion of the surface area of the object be proportional to? • ΔT • 2ΔT • ΔT2 • The surface area won’t change with temperature. • None of the above

  11. Area & Volume Expansion (of solids) • The equations: b = … g = …

  12. Thought question (ungraded): • Two jars of gas: helium and neon. Both have the same volume, same pressure, same temperature. Which jar contains the greatest number of gas molecules? (The mass of a neon molecule is greater than the mass of a helium molecule.) • jar of helium • jar of neon • same number

  13. Ideal Gas Law • Hold T constant, then V decreases as P increases • Hold P constant, then V increases as T increases • Hold P, T, constant, then V increases as #molecules increases • Summary:

  14. Quick Writing • Ralph is confused…the book calls two different equations “the ideal gas law”: “PV = nRT”, and “PV = NkBT”. Why are they both called the ideal gas law, when only the first equation looks like what he learned in chemistry? Important stuff: P must be in _______ V must be in _______ T must be in _______ n = ________ R = ________ N = ________ kB = ________ What’s a mole? How are R and kB related?

  15. Ideal Gases: • Molecules collide like superballs (elastic) due to repulsive forces • No attractive forces • Never condense into liquids or solids • Are like “frictionless surfaces”, “massless pulleys”, fluids without viscosity, projectiles without air resistance, etc.  That is, they don’t really exist, but are useful constructs

  16. Demos/Videos: • Video: “barrel crush” • Demos: More liquid nitrogen! • Two balloons • Rubber nail • “Balloon pop” • Expansion ratio

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