PHYSICS – PHY1020-EXAM 1 (Wednesday 2/19) STUDY GUIDE Chapter 1: - *Coal reserves in US expected to last for: - Answer: Hundred of years - *Power: - Answer: Watts - *Kinetic Energy: - Answer: Calories - *Asteroid— Earth— dinosaurs: - Answer: It got very hot. - 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 19th 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 - -> a single 40 W bulb running 10 hr/day for a year uses about 150 kWh/yr - -> my refrigerator = 459 kWh/yr…more than per capita averages of 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. - Reflected means back out to space. - 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. Chapter 2: ATOMS & HEAT - Thermal Energy = Random motion of atoms; Ordered motion is NOT thermal energy - Adding 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? - Answer: The latent heat of evaporation of water is huge and it takes a long time for the stove to supply that much energy. - Molecular Water: liquid water is linked together due to electrical attraction and has an enormous specific heat. - 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: - Answer: No heat will flow between the bowls. - 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 - 2nd Law of Thermodynamics: Entropy in a thermally isolated system never decreases. - Entropy=the DISORDER or RANDOMNESS in a system. - Heat flow & Entropy Change: When we cool a hot region, we decrease its entropy, but not by much; When we heat a cool region, we increase its entropy by A LOT so this works OK. - EFFICIENCY: Heat engines work best with LARGE temperature difference. - Heat pump – uses outside air as thermal energy. You pay only for the electricity needed to move it inside. - *If gasoline engine produces a hotter explosion, the efficiency of the engine should: - Answer: Go up. - *The temperature warms by 2 degrees Celsius. That is approximately the same as: - Answer: 4 degrees F. - *Refrigerator with its door open is operating in a room. It: - Answer: Warms the room. - *If you double the energy content of a kg of gas, the temperature of the gas (measured on the absolute K scale): - Answer: DOUBLES. - *WATER MELTS AT: - Answer: 100 degrees F - *A table has the same temperature as the air above it. That means that the molecules in the air and in
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