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Announcements 9/5/12

Stay updated with classroom announcements, physics topics, demonstrations, and solved problems. Engage in interactive clicker questions and explore essential physics concepts. Enhance your understanding through engaging videos and demos. Join us for a fun and educational experience!

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Announcements 9/5/12

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  1. Announcements 9/5/12 • Prayer • Please introduce yourself to 4 people sitting near you before class • Anyone need a class directory? • (1+x)n≈ 1 + nx Frank & Ernest

  2. From warmup Extra time on? When we make the simplifying assumption when deriving that ß=3a, why can we eliminate some of the terms but not all of them? constant-volume gas thermometer triple point of water ideal gas law Other comments?

  3. Airplane Wings Principle 1: deflection Principle 2: Bernoulli “airfoils” http://www.av8n.com/how/htm/airfoils.html

  4. Curve balls Ball moving to the right (i.e. air moving to the left), with topspin  Ping pong demo!

  5. Worked Problem: The faucet of radius r2 = 2 cm puts water out at 15 liters/minute. The pressure at the opening of the faucet is about 1 atm. The water main (r1 = 6 cm) is 3 m below the faucet. What is the speed of the water in the narrow pipe? What is the pressure in the main? faucet r2 Pmain 3m r1 Answers: 0.199 m/s; 1.307E5 Pa = 1.290 atm

  6. Clicker question: Abs. 0 Room T 0 0 0 0 • The following represent the Celsius, Fahrenheit, Kelvin, and Rankine scales. (Rankine is like Kelvin, but for F instead of for C.) Which corresponds to the Celsius scale? Each tick mark = 20 deg.

  7. Demos: “What’s a thermometer?” • Liquid bulb thermometer • Constant volume thermometer

  8. 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?

  9. Thermal expansion • What went wrong here?

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

  11. From warmup To make a very sensitive glass thermometer, which liquid would be the best choice: mercury, alcohol, gasoline, glycerin, or water? Gasoline. It has the highest volume expansion coefficient of mercury, alcohol, gasoline, and glycerin; and, it has a larger range of temperatures at which it is a liquid than water.

  12. From warmup Two spheres are the same size and are made of the same material, but one is solid and the other is hollow. Which expands more when the temperature is increased? Explain. Both spheres expand the same amount, as a cavity within an object expands in the same way as if it were filled with the same material that the object is made of.

  13. From warmup: • At room temperature, the sphere just barely fits through the ring. (A) After the sphere is heated, it cannot be passed through the ring. Explain. (B) What if the ring is heated…can the sphere pass through? Explain. (A) The metal of the sphere has expanded and no longer fits through the ring. (B) The sphere will be able to pass through more easily than originally because the ring has expanded, including the hole in the ring.

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

  15. Clicker question: • If the expansion of all of the linear dimensions of an object is by a factor of 10-5 per degree, what should be the expansion factor of the surface area of the object? • 10-5 per degree • 210-5 per degree • 10-10 per degree

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

  17. Clicker question: • 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

  18. Ideal Gas Law • Hold T constant, then as P increases V will decrease • Hold P constant, then as T increases V will increase • Hold P, T, constant, then as #molecules increases V will increase • Summary:

  19. 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 = ________ Units of PV? What’s a mole? How are R and kB related?

  20. Ideal Gases: • Molecules collide like superballs (elastic) due to repulsive forces • No attractive forces • Don’t 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

  21. Image from Wikipedia: http://en.wikipedia.org/wiki/Atmospheric_pressure • Video: “Barrel crush” Bottle sealed at 14,000 feet Picture at 9,000 feet Picture at 1,000 feet

  22. Demos/Videos: • Demos: Liquid nitrogen! • Two balloons • Rubber nail • “Balloon pop” • “Nitrogen Tower” • Calculation (if time): How much volume will 1 liter of liquid nitrogen fill when it becomes gas? • Density of LN = 0.807 g/cm3 • Molar mass of N2 = 28 g/mol • Temperature in this room = 70 F • Atmospheric pressure in Provo today? 0.85 atm Answer: 821 L

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