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. - 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. - *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 - 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
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