Physics for Future Presidents Lecture 1 Trivia Electricity from a AAA battery costs you about 1000 per kilowatt hour 3 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 choice 2 hw assignments a week due every Tuesday at 12pm 1 2 3 4 3 exams 50 points Best 10 of Hw Essays 30 points Weekly he quizzes 10 points Weekly iclicker points 10 points An A B is 85 points Office is at 617 Keen walk ins welcome Scientific Notation calculator notation 1 5E6 excel notation 10 5 2E5 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 Calorie 1 kWh 1000 Calories in 2002 the US was using 97 Quads of energy in 2009 it went down to 94 6 probably due to recession Sectors of energy consumption Industrial Transportation Residential Commerical Trivia 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 energy 1 Watt 1 Joule per second 1 kilowatt 1000 joules per second 1 horsepower 1 kW actually 746 W down to 80x Hydrogen as Fuel 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 even though 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 must take into account that batteries must be replaces after 700 1000 recharges 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 burning Gasoline 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 release How fast do meters go when they hit the Earth Radius of Earth orbit 150 million km Circumference 942 million km Speed is 942 million km 365 x 24 x 60 x 60 30 km sec about 165x more energy per pound than TNT Dec 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 systems
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