PHYSICS PHY1020 EXAM 1 Wednesday 2 19 STUDY GUIDE updated 2 12 14 11 45PM Chapter 1 Coal reserves in US expected to last for Answer Hundreds of years Units of Power Answer Watts and horsepower Power is Answer ENERGY divided by TIME Kinetic Energy Answer Calories Asteroid Earth dinosaurs Answer It got very hot Smart Rocks Answer Used for ballistic missile defense Hybrid vehicles run on Answer Electric power and gasoline The main reason hydrogen driven automobiles haven t replaced gasoline ones Answer Hydrogen is too difficult to store in an automobile Compared to an equal weight of gasoline U 235 can deliver energy that is greater by a factor of Answer One million Which of the following contains the most energy per gram Answer choose uranium Compare the energy in a kilogram of flashlight batteries Answer the gasoline has about 10 times as much energy Which is the least expensive for the same energy delivered Answer CHOOSE COAL The kinetic energy for a typical 1 gram meteor is approximately equal to the energy of Answer 150 grams of TNT Which of the following contains the most energy per gram Answer choose uranium ONE WATT IS EQUIVALENT TO Answer ONE JOULE SECOND Most of the hydrogen we use in the U S comes from Answer Hydrogen produced in nuclear reactors If you DOUBLE the energy content of a kilogram of GAS the temperature of the gas measured on an absolute K scale Answer DOUBLES About how fast are molecules in air moving Answer The speed of light a single 40 W bulb running 10 hr day for a year uses about 150 my refrigerator 459 kWh yr more than per capita averages of Energy poverty about 1 2 billion people do not have access to electricity 2 8 billion rely on wood crop waste dung other biomass to cook heat their homes Late 19 th C we figured out how to generate electricity properly make good use of it Energy access correlates positively with life experiences US Average 13 400 kWh yr per capita kWh yr countries like Ethiopia Nigeria etc COMBINED To give access to all need TRIPLE the number of power plants Energy is conserved but it is complicated to the point that it s not particularly useful Theoretically all energy to earth is from the sun which 6 gets reflected by the atmosphere 20 reflected by clouds 4 reflected from earth s surface 51 absorbed by land oceans 3 absorbed by clouds 16 absorbed by atmosphere Kinetic energy QUADRUPLES when Speed DOUBLES so a car crashes at 30 MPH instead of 15 MPH there is 4X as much energy released to destroy things Reflected means back out to space A human running up the stairs can briefly use power of approximately Answer 1 Horsepower The atom with the fewest protons Answer HYDROGEN Electricity from an AAA costs the consumer about Answer 1000 per kilowatt hour Chapter 2 ATOMS HEAT Adding thermal energy Thermal Energy Random motion of atoms Ordered motion is NOT thermal energy Release internal potential energy usually chemical often burning Move thermal energy heat by convection moving masses of hot matter or conduction still mass but heat flow by atomic collisions Thermal Energy through solids and radiation Even when a tile floor has the same temperature as a carpeted one the tile feels cooler to your bare feet why ANSWER The tile floor has a LARGER thermal conductivity so heat flows out of your feet more rapidly as it warms a larger region of tile About how fast are molecules in air moving ANSWER 1000 feet second also speed of sound in air Temperature is a measure of Answer Average Kinetic Energy Heat flow through empty space NO atoms present Answer Radiation Wasted Energy Results from ANSWER The Laws of Physics Hand in hot oven doesn t hurt but would if you touch the metal burn immediately why ANSWER Hot air poor conductor of heat Metal good conductor of heat Temperature thermal energy results in several kinds of motion 1 Kinetic energy KE 1 2 mv 2 2 rotation energy 3 vibration energy Temperature is proportional to average kinetic energy or Velocity 2 Temperature is not equivalent to affect by rotation vibration of atoms molecules Melting Temperature of an object is usually equal to its freezing point For most materials at most temperatures If we add thermal energy the temperature rises and if we remove thermal energy the temperature drops common sense but there are exceptions and one of the most important exceptions is common dihydrogen oxide H2O or water Thermal Expansion almost always if temperature increases the material expands and the distance between atoms or molecules gets larger common sense e g St George Island Bridge thermal expansion joints Thermal Radiation Emission and absorption are affected by the surface of the object Absorption if surface is shiny or white it reflects a lot and absorbs little and stays cooler If surface is dark or black it absorbs a lot and reflects little and gets hotter Emission if the surface is shiny or white i e snow it emits poorly and stays hotter if the surface is dark black i e soil it emits fast and gets cooler faster Latent Heat the heat required to change a phase at constant temperature A kettle of water heats up rapidly but it takes a long time to boil away WHY stove to supply that much energy Answer The latent heat of evaporation of water is huge and it takes a long time for the Molecular Water liquid water is linked together due to electrical attraction and has an enormous specific heat Answer No heat will flow between the bowls Sticky Water The surface tension of water comes from the molecules sticking together electrically it takes A LOT of ADDED energy to BREAK the electrical bonds holding the sticky water together You are in the Kitchen with 3 mixing bowls One is metal second is glass and third is plastic All three are at exactly same temperature the 68 degrees F 20 degrees C temperature of the room If you touch the 3 bowls together 0th Law of Thermodynamics If 2 objects are not in thermal equilibrium heat will flow from the hot object to the cold object until their temperatures are equal 1st Law of Thermodynamics CONSERVATION OF ENERGY cannot be created nor destroyed The air in this room consists of countless tiny independent molecules You can be sure that these air molecules will not all shift spontaneously to the other side of the room leaving you in a vacuum because that would Answer Be extremely unlikely and therefore violate the 2nd law of thermodynamics Entropy the DISORDER or RANDOMNESS in a system 2nd Law of Thermodynamics Entropy in a thermally isolated system never decreases
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