Chapter 2 Atoms and Heat Laws of Thermodynamics Law 0 Objects in contact tend to reach the same temperature Law 1 Energy is conserved Law 2 Extracting useful energy from heat required a temperature di erence Law 3 The entropy of the universe is always changing Atoms Atoms are about 10 8cm in diameter There are about 50 000 of them in the diameter of a red blood cell smallest object visible with visible light Temperature Kinetic Energy Heat is the shaking of molecules kinetic energy In a solid despite shaking atoms remain in the same place If two objects have the same temperature their average kinetic energy is the same The speeds of the molecules are not the same a lighter molecule will have a higher velocity than a heavy one lightest molecules are in hydrogen gas Temperature can be measured in Fahrenheit or Celsius Physicists use kelvin Most objects expand when they get warm Heat can be transferred by conduction convection and radiation An explosion occurs when an object gets so much energy it quickly turns into a hot gas Energy converted into heat cannot be converted back e ciently Entropy is a measure of the disorder in molecules Warm objects have high entropy Book Quiz practice Questions If you double the energy content of a kilogram of gas the temperature of the gas measured on the absolute K scale is unchanged A increases by the square root of 2 B doubles C is multiplied by 4 D 1 2 3 About how fast are molecules in air moving A B C D 1000 ft sec the speed of light 9 8 m sec 9 8 cm sec Temperature is the measure of average momentum A average kinetic energy B average velocity C 4 5 6 7 8 9 11 D average total energy zero since they don t move In a bucket of water the instantaneous speed of the molecules is closest to A B whatever speed the wood is moving approximately 1 7 meters per second C approximately 1000 feet per second D approximately 186 000 miles per second E A refrigerator operating in a room A warms the room B C D cools the room has no e ect on the room removes water vapor from the room A refrigerator with its door open is operating in a room It A warms the room B C D cools the room has no e ect on the room removes water vapor from the room A table has the same temperature as the air above it That means that the molecules in the air and in the table have A B C D the same average velocity the same average energy the same acceleration the same average mass Ice melts at 0 K A 0 C B 0 F C 100 C D A gas heater warms a room mostly through convection A conduction B C radiation D depletion 10 The velocity of sound A B C D increases when the temperature increases decreases when the temperature increases depends on the pressure of the air is constant independent of the temperature If gasoline engine produces a hotter explosion then the e ciency of the engine should A B C be the same go up go down 17 12 A cup full of water and made of plastic feels warmer than one made of glass because plastic is warmed by water plastic conducts heat less than glass plastic conducts heat better than glass A B C D plastic dissolves in water 13 The atom with the fewest number of protons is 14 How many atoms are there in the width of a human hair About A B C D A B C D helium carbon hydrogen oxygen 25 125 000 273 000 000 000 6 x 1023 15 The speed of sound is approximately 1 foot per nanosecond 1 foot per second 1000 feet per second 186 000 miles per hour A B C D 16 Put a hot glass in cool water The glass shatters because A B C D it heats the surface water to boiling the outer surface of the glass contracts rapidly but the inner part doesn t the outer surface of the glass expands rapidly the rapid conduction of heat triggers strong vibrations expanding sea water Sea level is rising from global warming The main cause is A B melting glaciers C D expanding rock under the sea contracting earth while the water stays constant 18 The temperature warms by 2 C That is approximately the same as A B C D 1 F 2 F 4 F 1 2 F 19 Heat a room using the least energy by burning natural gas methane A using natural gas to run a heat pump B burning coal C D burning gasoline 20 There is almost no hydrogen gas in the atmosphere because it escapes the Earth s gravity there is very little hydrogen in the oceans or land hydrogen molecules move slower than oxygen and nitrogen hydrogen has all sunk to the Earth s core 21 At Mach 10 if all the energy of a meteorite went into heating the meteorite its temperature would be about 22 The New Orleans levees failed because thermal expansion broke therm they were made of continuous concrete that could not stand the pressure they had leaks at the thermal expansion joints they were weaker at the thermal expansion joints If temperature rises by 5 C 9 F then the rise in sea level will be about A B C D 2 inches 2 feet 12 feet 97 feet 24 For a typical auto the fraction of the gasoline energy wasted as heat is about careful this may be a trick 300 C 6000 C 30 000 C 100 000 C question 1 A 10 B 20 C 80 D A B C D A B C D A B C D 23 25 The temperature of the sun A B C D is always hotter than in the shade is always the same as in the shade is sometimes cooler than int he shade is not well defined 26 When a material is cooled it stays the same size is contracts it expands Some materials contract and some expands A B C D 27 The melting temperature of an object is usually A B C D equal to its freezing point higher than the freezing point lower than the freezing point equal to the boiling point 28 Absolute zero is the temperature of A frozen water 29 When a liquid boils the increase in volume liquid to gas is typically a factor of the Universe liquid helium nothing 10 100 1000 1 000 000 B C D A B C D 30 If the temperature of a gas in a container goes A B C D become infinite stay the same double become 3000 times larger 31 Firewalking is similar to A water on a sauce pan B C D water skiing the space shuttle reentry an automobile airbag 32 For gasoline to explode it needs to be mixed with oxygen A to be mixed with nitrogen B …
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