Thermal Expansion. When the temperature of a metal ring increases, does the hole become larger? Smaller? Or stay same?

Transcription

1 Thermal Expansion When the temperature of a metal ring increases, does the hole become larger? Smaller? Or stay same?

2 QuickCheck 15.6 Two blocks are of identical size. One is made of lead and sits on the bottom of a pond; the other is of wood and floats on top. Upon which is the buoyant force greater? A. On the lead block. B. On the wood block. C. They both experience the same buoyant force. Slide 15-74

3 QuickCheck 15.6 Two blocks are of identical size. One is made of lead and sits on the bottom of a pond; the other is of wood and floats on top. Upon which is the buoyant force greater? A. On the lead block. B. On the wood block. C. They both experience the same buoyant force. The fully submerged lead block displaces more much water than the wood block. Slide 15-75

4 QuickCheck 15.9 Water flows from left to right through this pipe. What can you say about the speed of the water at points 1 and 2? A. v 1 > v 2. B. v 1 = v 2. C. v 1 < v 2. Slide 15-87

5 QuickCheck 15.9 Water flows from left to right through this pipe. What can you say about the speed of the water at points 1 and 2? A. v 1 > v 2. B. v 1 = v 2. C. v 1 < v 2. Continuity: v 1 A 1 = v 2 A 2 Slide 15-88

6 QuickCheck A gas in a container expands rapidly, pushing the piston out. The temperature of the gas A. Rises. B. Is unchanged. C. Falls. D. Can t say without knowing more Pearson Education, Inc. Slide 17-89

7 QuickCheck A gas in a container expands rapidly, pushing the piston out. The temperature of the gas A. Rises. B. Is unchanged. C. Falls. D. Can t say without knowing more Pearson Education, Inc. Slide 17-90

8 QuickCheck A gas in a container expands rapidly, pushing the piston out. The temperature of the gas falls. This is because A. The gas pressure falls. B. The gas density falls. C. Heat energy is removed. D. Work is done. E. Both C and D Pearson Education, Inc. Slide 17-95

9 QuickCheck A gas in a container expands rapidly, pushing the piston out. The temperature of the gas falls. This is because A. The gas pressure falls. B. The gas density falls. C. Heat energy is removed. D. Work is done. E. Both C and D Pearson Education, Inc. Slide 17-96

10 Today s Quiz: Was ist das? Fig. 20-9, p. 569

11 Which goes with it?

12 30 is HOT. 20 is NICE. 10 is CHILLY. Zero is ICE!

13 Thermal Expansion: Linear L L T Coefficients determined experimentally! 0

14 Thermal Expansion: Volume V V T ~ 3 0

15 Thermal Expansion: Linear

16 Thermal Expansion: Linear The coefficient of linear expansion of steel is 12 x 10-6 / C. A railroad track is made of individual rails of steel 1.0 km in length. By what length would these rails change between a cold day when the temperature is -10 C and a hot day at 30 C? L L T 6 3 L (12 x10 / C)(10 m)(30 C ( 10 C)) 0 L 0.48m

17 Thermal Expansion: Linear L L T What change in temperature is needed to fill the gap, 1.3 x 10-3 m? 0 brass 19x10 C 23x10 C AL 3 Lbrass LAl 1.3x10 m 3 1.3x10 m T L L brass brass Al Al C

18 Thermal Expansion When the temperature of a metal ring increases, does the hole become larger? Smaller? Or stay same?

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20 Circle Expansion L L T 0 The coefficient of linear expansion of aluminum is 23 x 10-6 /C. A circular hole in an aluminum plate is cm in diameter at 0 C. What is the diameter of the hole if the temperature of the plate is raised to 100 C? 6 (23x10 / C)(2.725 cm)100 C 6.3x10 3 cm d 2.731cm

21 The First Law of Thermodynamics E Q W int The First Law of Thermodynamics is a special case of the Law of Conservation of Energy It takes into account changes in internal energy and energy transfers by heat and work Although Q and W each are dependent on the path, Q + W is independent of the path

22 Work in Ideal-Gas Processes W: Work On a pv diagram, the work done on a gas W has a nice geometric interpretation. W = the negative of the area under the pv curve between V i and V f. W V V f i P dv Slide 17-28

23 Q: Heat The change of internal energy of a system due to a temperature or phase change is given by: Temperature Change: Q = mc T Phase Change: Q = ml Q is positive when the system GAINS heat and negative when it LOSES heat.

24 Specific Heat: Thermal Inertia The Specific Heat of a substance is the amount of Energy it requires to raise the temperature of 1 kg, 1 degree Celsius. Q Q J mc T c 0 m T kg C The higher the specific heat, the more energy it takes and the longer it takes to heat up and to cool off. The lower the specific heat, the less energy it takes and the quicker it takes to heat up and cool off. Substances with HIGH specific heat STORE heat energy and make good thermal moderators. (Ex: Water, Oceans)

25 Specific Heat c c c water glycerin iron J 4186 kg Why does water have such a high specific heat? Heat goes into other modes of energy so that temperature changes slowly. 0 0 J 2410 kg J 452 kg C C 0 C

26 Q mc T How much heat is required to raise the temperature of a 0.750kg aluminum pot containing 2.50kg of water at 30ºC to the boiling point? Q m c T m c T Al Al w w m AlcAl mwcw T.75 kg(900 J / kg C) 2.5 kg(4186 J / kg C) (70 C) Q 7.798x10 5 J

27 Phase Change Q ml A change from one phase to another A phase change always occurs with an exchange of energy! A phase change always occurs at constant temperature!

28 Sample Latent Heat Values Q ml

29 Phase Change: Melting & Freezing Melting: Solid to the melting temperature Melting is a cooling process Freezing: Liquid to the melting temperature Freezing is a warming process.

30 Phase Change: Melting & Freezing Melting: Energy goes into the system and breaks molecular bonds.. Freezing: Energy is given up by the system by forming molecular bon

31 Phase Change: Melting & Freezing

32 Why do farmers spray peaches with water to save them from frost? Freezing is a warming process!

33 If you were in an igloo on a freezing night. You would be warmed more by a) a bucket of ice melting. b) a bucket of water freezing c) the same either way. d) neither - are you nuts?

34 Phase Change: Evaporation Takes place at the surface of a liquid due to escaping molecules. Occurs at all temperatures Evaporation occurs when water vapor pressure in the liquid exceeds the pressure of water vapor in the surrounding air. Evaporation is a cooling process.

35 Evaporation is a Cooling Process

36 Phase Change: Boiling Boiling is evaporation under the surface of the liquid. Liquid boils at the temperature for which its vapor pressure exceeds the external pressure (mostly atmospheric pressure.) Boiling point depends on temperature AND 1 atm, bp of water is 5atm, bp of water is 374 ºC Boiling is a cooling process. At low pressures, liquids are boiled ( freeze-dried ) into solids.

37 Phase Change: Condensation Gas molecules condense to form a liquid. Condensation is a warming process Why is a rainy day warmer than a cloudy or clear day in winter? Why do we feel uncomfortable on a muggy day?

38 Condensation is a Warming Process

39 Phase Change: Humidity Vapor is the gas phase of a substance below its boiling temperature. Air can hold only so much water vapor before it becomes saturated and condensation occurs. Humidity is a measure of vapor density. Warm air can hold more water vapor. More condensation occurs at cooler temperatures because the molecules are moving slower. Slow moving water molecules coalesce upon collision.

40 High Pressure Dry Warm Weather Low Pressure Stormy Weather

41 Stormy Weather When warm air rises, it expands and cools. The water vapor in the air soon condenses into water droplets, which form clouds and eventually these droplets fall from the sky as rain.

42 Phase Change:Sublimation The conversion of a solid directly to a gas & visa versa Examples: snowflakes, Moth Balls, dry ice

43 Windward: Wet Leeward: Dry Cools and condenses at Top Warm Humid Air Pushed Up Warm Dry Air Falls Down

44 Phase Change: Triple Point A temperature and pressure at which all three phases exist in equilibrium. Lines of equilibrium Freezing-Melting Evaporation -Condensation Sublimation

45 Phase Change Q ml Phase change occurs at a Constant Temperature! Latent Heats of: Fusion & Evaporation L f, L v Water: L L f v 334 kj / kg solid-liquid 2256 kj / kg liquid-gas

46 Phase Change: Water Q ml How much 100 C does it take to melt 1kg of ice at -30 C? How much energy is needed to raise the ices to 0 C How much energy is needed to melt 1kg of ice? How much energy is given up by the steam? What happens to the steam that is melting the ice? L L f v 334 kj / kg 2256 kj / kg 0 cice 2090 J / kg C 0 cwater 4186 J / kg C

47 Phase Change: Water Q ml How much 100 C does it take to melt 1kg of ice at -30 C? How much energy is needed to raise the ices to 0 C L L f v Q kg J kg C C 62700J 334 kj / kg 2256 kj / kg 0 cice 2090 J / kg C 0 cwater 4186 J / kg C (2090 / )(30 )

48 Phase Change: Water Q ml How much 100 C does it take to melt 1kg of ice at -30 C? How much energy is needed to melt 1kg of ice? Q2 ml 1 kg(334 kj / kg) Q2 334kJ L L f v 334 kj / kg 2256 kj / kg 0 cice 2090 J / kg C 0 cwater 4186 J / kg C Q J Q2 334kJ

49 Phase Change: Water Q ml How much 100 C does it take to melt 1kg of ice at -30 C? How much energy is given up by the steam? What happens to the steam that is melting the ice? L L f v 334 kj / kg 2256 kj / kg 0 cice 2090 J / kg C 0 cwater 4186 J / kg C Q J Q2 334kJ Qtotal 397kJ

50 Heat flows from HOT to COLD Conduction (solids) Convection (liquids & gases) Radiation (solids, gases, plasma)

51 Any two systems placed in thermal contact will have an exchange of heat energy until they reach the same temperature. If the systems are in thermal equilibrium then no net changes take place.

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53 Energy transferredvia molecular collisions

54 Heat energy is transferred in solids by collisions between free electrons and vibrating atoms. Good Conductors: Most Metals (free electrons!) Bad Conductors: Organic & Inert Materials Good Insulators: Air, Water, Wood Good Conductors are BAD Insulators & Visa Versa

55 The heat Q conducted during a time t through a material with a thermal conductivity k. dt/dx is the Temperature Gradient. dt P ka dx

56 Some Thermal Conductivities

57 Temperature Gradient The quantity dt / dx is called the temperature gradient Q t ka dt dx dt T T h dx L c

58 Conduction Problem T L T h c ka A bar of gold is in thermal contact with a bar of silver of the same length and area as shown. One end of the compound bar is maintained at 80.0 C while the opposite end is at 30.0 C. When the energy transfer reaches steady state, what is the temperature at the junction? Ignore thermal expansion of the metals.

59 In the same room, at the same temperature, the tile floor feels cooler than wood floor. How can they be the same temperature?

60 Hot Air rises, expands and cools, and then sinks back down causing convection currents that transport heat energy. Hot air rises because fast moving molecules tend to migrate toward regions of least obstruction - UP - into regions of lesser density! Rising air cools because a decrease in density reduces number of collisions & speeds decrease. As the air cools, it becomes denser, sinking down, producing a convection current.

61 Uneven heating on the earth and over water cause convection currents in the atmosphere, resulting in WINDS. Global wind patterns (Trade Winds, Jet Streams) are due to convection current from warmer regions (equator) to cooler regions (poles) plus rotation of Earth. Convection Currents in the Ocean (Gulf Stream) transport energy throughout the oceans. Air & Ocean Convection causes the WEATHER.

62 Convection between water and land causes the Winds.

63 Sea Breeze

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66 Electromagnetic Radiation is emitted and absorbed via atomic excitations. All objects absorb and emit EM waves.

67 Frequency ~ Temperature When an object it heated it will glow first in the infrared, then the visible. Most solid materials break down before they emit UV and higher frequency EM waves. Long Short

68 A good absorber reflects little and appears Black A good absorber is also a good emitter.

69 How do fur coats keep you warm? Fur is filled with air. Convection currents are slow because the convection loops are so small.

70 Stefan s Law P = σaet 4 P is the rate of energy transfer, in Watts σ = x 10-8 W/m 2. K 4 A is the surface area of the object e is a constant called the emissivity e varies from 0 to 1 The emissivity is also equal to the absorptivity T is the temperature in Kelvins

71 P 4 e T A Radiant heat makes it impossible to stand close to a hot lava flow. Calculate the rate of heat loss by radiation from 1.00 m 2 of 1200C fresh lava into 30.0C surroundings, assuming lava s emissivity is 1. The net heat transfer by radiation is: P e A( T T ) P e A( T T ) (5.67 x10 J / smk )1 m (( K) ( K) ) P 266kW

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73 Why is winter cold and summer hot?

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75 Intensity: The Radiation Power, P, passing through an area, A. I P W r m

76 Assume that the sun is a sphere of radius 6.96 x 10 8 m and that its surface temperature is 5.8 x 10 3 K. a) If the sun is a perfect emitter, at what rate is energy emitted from the surface of the sun? b) What is the rate per square meter at the sun's surface - that is, the Intensity? c)what is the Intensity at which energy is received on Earth in one hour? Ignore effects of absorption due to the atmosphere. The average distance from the Earth to the sun is 1.50 x m. I P 4 r P 4 2 e T A

77 The Solar Constant

78 Solar Cycle: 11 year Cycle e-primer_prt.htm

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81 Alan Robock Department of Environmental Sciences Tambora in 1815, together with an eruption from an unknown volcano in 1809, produced the Year Without a Summer (1816)

82 Tambora, 1815, produced the Year Without a Summer (1816) Darkness by Byron I had a dream, which was not all a dream. The bright sun was extinguish'd, and the stars Did wander darkling in the eternal space, Rayless, and pathless, and the icy earth Swung blind and blackening in the moonless air; Morn came and went and came, and brought no day, And men forgot their passions in the dread Of this their desolation; and all hearts Were chill'd into a selfish prayer for light: And they did live by watchfires and the thrones, The palaces of crowned kings the huts, The habitations of all things which dwell, Were burnt for beacons; cities were consumed, And men were gather'd round their blazing homes To look once more into each other's face;... Alan Robock Department of Environmental Sciences

83 Tambora, 1815, produced the Year Without a Summer (1816) Percy Bysshe Shelley Mary Shelley John Polidori Alan Robock Department of Environmental Sciences

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85 During periods of high activity, the Sun has more sunspots than usual. Sunspots are cooler than the rest of the luminous layer of the Sun s atmosphere (the photosphere). Paradoxically, the total power output of the active Sun is not lower than average but is the same or slightly higher than average. Work out the details of the following crude model of this phenomenon. Consider a patch of the photosphere with an area of m 2. Its emissivity is (a) Find the power it radiates if its temperature is uniformly K, corresponding to the quiet Sun. (b) To represent a sunspot, assume that 10.0% of the area is at K and the other 90.0% is at K. That is, a section with the surface area of the Earth is K cooler than before and a section nine times as large is 90 K warmer. Find the average temperature of the patch. (c) Find the power output of the patch. Compare it with the answer to part (a).

86 Why are cloudy nights warmer than cold nights?

87 The heating effect of a medium such as glass or the Earth s atmosphere that is transparent to short wavelengths but opaque to longer wavelengths: Short get in, longer are trapped!

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89 CO 2 & Temperature Change

90 Impacts of a Warming Arctic The Arctic Climate Impact Assessment, a study commissioned by the United States and the seven other countries with Arctic territory, projects that rising global concentrations of heat-trapping emissions will drive up temperatures particularly quickly at high latitudes.

91 RISING SEAS One of the most important consequences of Arctic warming will be increased flows of meltwater and icebergs from glaciers and ice sheets, and thus an accelerated rise in sea levels.

92 Forrest vs Tundra Caught between rising seas on one side and expanding shrub-filled zones to the south, tundra ecosystems around the Arctic will likely shrink to their smallest extent in at least 100 years, the scientists concluded. This could reduce breeding areas for many tundra-dwelling bird species and grazing lands for caribou and other mammals.

93 1 Meter Rise In Florida

94 ZEPO:A Melting Glacier in Tibet "Thirty years ago, there was no river here. If you come back here in another 30 years, one thing is for sure: There will definitely be no more ice here." -Dr. Yao Tandong, Institute of Tibetan Plateau Research

95 Global Glacial Ice Melting On Kilimanjaro in Kenya, an 11,700-year-old ice cap that measured 4.3 square miles in 1912 had shrunk to 0.94 square miles in 2000, and is projected to disappear altogether in about 15 years. Melting of glaciers in Patagonia has doubled in recent years.

96 Ice Caps Melting in Peru In Peru, the Quelccaya ice cap retreated a rate of more than 600 feet a year from 2000 to up from just 15 feet a year in the 1960's and 70's - leaving a vast 80-foot-deep lake where none had existed when his studies began.

97 It is much too late for sustainable development; what we need is a sustainable retreat. -James Lovelock, The Revenge of Gaia

98 The Gaia Theory The organic and inorganic components of Planet Earth have evolved together as a single living, self-regulating system Life maintains conditions suitable for its own survival. - James Lovelock

99 Our Spaceship Earth One island in one ocean...from space...we re all astronauts aboard a little spaceship called Earth - Bucky Fuller

100 67,000 miles/hr 500,000 miles/hr "We are on a spaceship; a beautiful one. It took billions of years to develop. We're not going to get another. - Bucky Fuller, Operating Manual for Spaceship Earth

101 A sample of an ideal gas goes through the process as shown. From A to B, the process is adiabatic; from B to C, it is isobaric with 100 kj of energy entering the system by heat. From C to D, the process is isothermal; from D to A, it is isobaric with 150 kj of energy leaving the system by heat. Find everything out and fill out the table. Problem