Physics for Future Presidents: Lecture 1Trivia: Electricity from a AAA battery costs you about...$1000 per kilowatt hour3 Unit Exams: Wed Feb 20th 8:30am-1:00 pm Wed Apr 10th 8:30am-1:00 pm Tue Apr 30th 8:30am-1:00 pm (finals week)-all are multiple choice2 hw assignments a week, due every Tuesday at 12pm.1) 3 exams 50 points2) Best 10 of Hw Essays 30 points3) Weekly he quizzes 10 points4) Weekly iclicker points 10 pointsAn A-/B+ is 85 points.Office is at 617 Keen, walk-ins welcomeScientific Notation: - calculator notation = 1.5E6- excel notation = 10^52E5 x 3E9 = 6E14 (numbers in front, multiply, exponents add)6E5/2E9 = 3E-4 (numbers in front divide, exponents subtract)- energy is the ability to do work, energy can be active (kinetic, moving) or stored (potential: mechanical, electrical chemical)- energy can be measured in: Joules, calories, Calories (1000 calories), kilowatt-hours (kWh), BTU’s, Quads (10^15 BTU’s)1 Wh ≈ 1 Calorie1 kWh ≈ 1000 Calories in 2002 the US was using 97 Quads of energyin 2009 it went down to 94.6 (probably due to recession)Sectors of energy consumption: Industrial, Transportation, Residential, CommericalTrivia: 1 pound of chocolate chip cookies have more energy than 1 pound of TNT- Flow of “stuff” at 5 gallons/min, how long will it take to full a 50 gal barrel (5gal/minute) x t minutes = 50 gallons then t=10 minutes- power = energy/time, power is a measure of the flow of energy1 Watt = 1 Joule per second1 kilowatt = 1000 joules per second1 horsepower ≈ 1 kW (actually 746 W)- energy = power x time (kilowatt is a unit of power, but a kilowatt-hour, power and time, is a unit of energy)- TNT is more powerful than cookies because it releases its energy very fast, eventhough cookies have more energy, they release it very slow (metabolic rates)- a car battery has 340x less energy per lb than an equal weight of gasoline- but since burning gasoline to make electricity is only 30% efficient, 340x goes down to 80x- must take into account that batteries must be replaces after 700-1000 rechargesHydrogen as Fuel:- we can’t mine H2, we have to use energy make it (water --> hydrogen + oxygen)- compared to gasoline, compressed H2 has 3x more energy per pound, but 6x less energy per gallon (3x less for liquid H2)- hydrogen boils at -432 F- we can use electricity to separate H2 and oxygen from water, using a fuel cell to combine H and O and make electricity without burningGasoline: high energy density, convenient to transport and store, no residue from burn-ing, was relatively cheap; but expensive compared to coal, contributes to atmospheric CO2; best use—cars(then)Hybrid: allows gas engine to operate more efficiently, uses energy from braking; batter-ies expensive to replace ($100/lb); best use—cars (now)Hydrogen Fuel Cell: even more energy density than gasoline (3x more energy/gram), water is the only waste; but dangerous to store, difficult to transport, takes up lots of space, “made” not mind; best use—bus, trucks, airplanes(cause of large space)Solar: renewable; but not enough space on car rooftop to generate 50-400 hp, only available during day, cells are expensive; best use—boats, planes?, power plants- kinetic energy: K = 1/2 mv^2, so kinetic energy quadruple when speed doubles- when a car crashes at 30 mph instead of 15, there’s 4x as much energy releaseHow fast do meters go when they hit the Earth?Radius of Earth orbit ≈ 150 million kmCircumference ≈ 942 million kmSpeed is 942 million km / (365 x 24 x 60 x 60) ≈ 30 km/sec, about 165x more energy per pound than TNTDec 11th 2012: asteroid zipped between our planet and the moon just two days after astronomers first spotted it, the near Earth asteroid came within 140,000 miles of our planet at about 5am on Tuesday December 11th (moon orbits at 240,000 mi). Asteroid is 120 feet wide, big enough to cause substantial damage. An object of similar size flat-tened 800 square miles of forest when it exploded above Siberia’s Tunguska River in 1908.- uranium has 30 million times more energy per pound than TNT- light bulbs: incandescent bulbs use electricity to heat a filament (phased out 2012-2014, LED bulbs coming in the next 5 years or so), but most of the energy goes to heat, not light- fluorescent bulbs use 4x less electricity for the same light, last 13x longer- theres about 1kW per sqr. meter if the sun is shining, but solar cells are only 15-40% efficient- the US uses 400 gigawatts, so to power the US it would take about Diet vs. Exercise:- about 1 hr of strenuous exercise = 367 Calories- if you reduce your Calories by 500 per day, you can lose 1 lb per week, but be careful with energy conservation, it can get complicated in biological
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