Published on February 22, 2008
The Sciences- An Integrated ApproachBy Trefil & Hazen Prepared by: Long Nguyen, Ph.D. Curry College, Milton: The Sciences- An Integrated Approach By Trefil & Hazen Prepared by: Long Nguyen, Ph.D. Curry College, Milton Chapter 3 Energy To think and ponder: Why must animals eat to stay alive?: To think and ponder: Why must animals eat to stay alive? Great Idea: Energy presents in many interchangable forms. Total amount of energy in an isolated system is conserved Daily Routine: spending energy : Daily Routine: spending energy Turn-on lights Showers – pump – water heater Coffee & breakfast: electricity/gas/other fuels Drive to work/school/beach Walk, Exercise,Think Breath, Heart Beats A Great Chain of Energy: A Great Chain of Energy Generated in the solar core To Solar surface in K of years To Earth in 8 mn Absorbed by algae through photosynthesis Algea died and settled on the seabed, buried! Under pressure and heat, dead algea turned into fossil fuel – aka Petroleum, aka oil Solar energy -> Fossil Fuel: Solar energy -> Fossil Fuel Source: http://www.eia.doe.gov/kids/energyfacts/sources/non-renewable/oil.html Solar energy -> Fossil Fuel: Solar energy -> Fossil Fuel Solar energy -> Fossil Fuel: Solar energy -> Fossil Fuel What’s in a 42-Gal Barrel of Oil?: What’s in a 42-Gal Barrel of Oil? Source: American Petroleum Institute (www.api.org). Figures are based on 1995 average yields for U.S. refineries. A Great Chain of Energy: the Food Chain: A Great Chain of Energy: the Food Chain Solar energy absorbed by plants through photosynthesis Plants are eaten by animals Small animals are eaten by bigger animals Human eats plants and animals A Great Chain of Energy: the Food Chain…: A Great Chain of Energy: the Food Chain… Source: www.stevetrash.com/ booking/lessons/fcreview.htm Work vs. Energy: Work vs. Energy Car burns fuel. Fuel energy turns the wheel. Body burns food & oxygen. Chemical reactions make muscle contract so we can walk. Work is done when a force is exerted over a distance. Work : Work Work is equal to the force that is exerted times the distance over which it is exerted. In equation form: Work (joules) = Force (newtons) x distance (meters) (pushing against the wall in futile: no work is being done!) 1 joule of work = 1 N of force x 1 meter of distance (Joule = N-m) Work…: Work… How much work do you do when you carry your 5kg book bag up 4 flights of stairs to your room? Hints: force = mass x g work =force x distance Work…: Work… How much work do you do when you carry your 5kg book bag up 4 flights of stairs (4m per flight) to your room? Force required: F = 5kg x 9.8 m/s2 = 49 newtons Work done: W = 49 N x 4m x 4 = 784 joules work =force x distance Energy – What is it? : Energy – What is it? Ability to do work, i.e. exerting a force over a distance. Recorded in the same unit of work: Joules, Nm’s, or foot-pounds Power – What is it? : Power – What is it? Rate at which work is done! Power is the amount of work done divided by the time it takes to do that work: Power (watts) = Work (joules) / time (seconds) 1,000 watts = 1 kilowatt – 1 horse-power = 550 fp/s Energy can also be measured in power x time Energy (joules) = P (watts) x t (seconds) Electric energy measured in Kilowatt-hour (kwh) James Watt (1736-1819), Scottish inventor who developed the steam engine that power the industrial revolution Power – What is it? : Power – What is it? Rate at which work is done! Power is the amount of work done divided by the time it takes to do that work: Power (watts) = Work (joules) / time (seconds) 1,000 watts = 1 kilowatt – 1 horse-power = 550 fp/s James Watt (1736-1819), Scottish inventor who developed the steam engine that power the industrial revolution Energy cost: Energy cost A 400-w stereo system was played for 5 hours every day, how much energy do you use per week? Hint: energy = P x t If the cost is 8 cents per kwh, how much do you owe the electric company in a month (4.2 weeks)? Slide19: Energy used per week: E = 400w x 5 hours/day x 7 days/week = 14,000 wh per week = 14 Kwh per week Cost per month: Cost = 8 cents x 14Kwhs/Week x 4.2 weeks/month = 470.4 cents = $4.70 A 400-w stereo system was played for 5 hours every day, how much energy do you use per week? If the cost is 8 cents per Kwh, how much do you owe the electric company in a month (4.2 weeks)? Kinetic Energy: Kinetic Energy Energy carried by an object in motion, e.g. speeding bullet, moving car, flying bird, etc. Kinetic Energy equals the mass of the moving object times the square of that object’s speed, times the constant ½. In equation: K.E (joules) = ½ x mass (kg) x [speed (m/s)]2 E = ½ mv2 Bowling Balls and Baseballs: Bowling Balls and Baseballs What is the K.E. of a 4kg bowling ball rolling at 10 m/s (22mph)? Compare it with a 250gram baseball traveling at 110mph (50m/s). Hint: E = 1/2mv2 What object would hurt you more if it hit you? (more K.E) Slide22: K.E.-bowlingball = ½ x 4kg x [8m/s)]2 = ½ x 4 x 64 = 128 kg-m2 K.E.-baseball = ½ x 0.25kg x [50m/s)]2 = ½ x 0.25 x 2500 = 312.5 kg-m2 What is the K.E. of a 4kg bowling ball rolling at 8 m/s (24mph)? Compare it with a 250gram baseball traveling at 110mph (50m/s). What object would hurt you more if it hit you? Potential Energy (P.E.): Potential Energy (P.E.) Energy that are stored in the objects and ready to be released. Gravitational P.E.: Balancing rocks, yo-yo Grav. P.E. = mass (kg) x g (m/s2) x height (m) Chemical P.E.: gasoline, food, battery Electrical P.E.: electrical outlets Elastic P.E.: rubber band, bungee cord Magnetic P.E.: magnet Elastic & Gravitational Energy: Elastic & Gravitational Energy Gravitational Energy: Gravitational Energy Heat or Thermal Energy: Heat or Thermal Energy Objects are made of moving atoms and molecules. When the particles collide they create heat. It’s related to kinetic energy Flows like a fluid from place to place Some materials absorb heat better than the others Benjamin Thompson & Sir Humphrey Davey created heat through friction Wave Energy: Wave Energy Surf, Tidal waves Sound waves Seismic waves Electromagnetic waves Possess kinetic energy Mass as Energy: Mass as Energy Certain atoms, such as Uranium, spontaneously release energy as they disintegrate: Mass is a form of energy E (joules) = m (kg)[c(m/s)]2 E = mc2 c: speed of light ; 3x109 m/s Energy Potential of Mass: Energy Potential of Mass How much P.E. is contained in a grain of sand with a mass of 0.002 gram? Hint: E = mc2 How much P.E. is contained in a grain of sand with a mass of 0.002 gram?: How much P.E. is contained in a grain of sand with a mass of 0.002 gram? E (joules) = mass (kg) x [speed of light (m/s)]2 = 2 X 10-6 kg x [3 x 108 (m/s)]2 = 2 x 10-6 x 9 x 1016 kg-m2/s2 = 18 x 1010 joules (approx 50,000 kwh) Average american family uses 1,000 kwh of electricity per month. The Interchangeability of Energy: The Interchangeability of Energy Light wave energy to chemical energy in plants and animals: photosynthesis Chemical energy to kinetic energy in muscle Kinetic energy to gravitational energy and back Bungee jumping, yo-yo Slinky ? Slide32: Bungee Jumping Kawarau Bridge Queenstown, New Zealand Bungee Jumping –AJ Hackett - Eiffel Tower (Jun-87): Bungee Jumping – AJ Hackett - Eiffel Tower (Jun-87) Bungee JumpingKawarau Bridge Queenstown, New Zealand : Bungee Jumping Kawarau Bridge Queenstown, New Zealand New Sources of Energy: New Sources of Energy Photovoltaic cells Wind power Hydro power Geo-Thermal power Energy for Life and Trofic Levels: Energy for Life and Trofic Levels Sun incoming energy: 1,400 w/m2 Total power received by earth’s top atmospheric surface: 1.79 x 10 17 watts 45% reached earth’s surface to supply the base of the food chain - photosynthetic organisms -> Herbivores –> Carnivores -> Big Carnivores First Law of ThermodynamicsConservation of Energy: First Law of Thermodynamics Conservation of Energy In an isolated system, the total amount of energy, including heat, is conserved. “Nothing is destroyed, nothing ever lost, but the entire machinery, complicated as it is, works smoothly and harmoniously…” James Prescott Joules
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