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CU-Boulder PHYS 3070 - Lecture Notes

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1http://www.rockthevote.org/Or if you are a Colorado residentyou can go directly to:http://www.elections.colorado.govI encourage everyone to participate in our elections.If you are interested in registration information, the followingweb page has an easy form for all states which then prints out the correct form filled out.In Colorado, you must register 29 days ahead of the election.1. Finish reading chapter 1, and start on chapter 2 of E&E.2. Homework #1 Solutions posted on the web page.3. Homework #2 Problems are due next Wednesday4. iClickers start counting as part of your grade this Monday !Note that starting Monday for the rest of the semester clicker scores count (but the lowest 5 classes are dropped).3 points (correct), 2 points (incorrect), 0 points (no answ).5. Note extra credit assignment #1 due next Wednesday6. Next extra credit assignment #2 – see next slideExtra Credit #2:The Energy and Climate Challenge: Have We Underestimated theSize of the Challenge?September 16, 20087:00 PM - 9:00 PMCU-Boulder, Humanities Rm 1B50Free and Open to the PublicFor flyer see: http://ei.colorado.edu/siteadmin/images/files/file_6.pdfGo to the panel discussion. Write up a one page summary of a couple of points you thought were particularly interesting. Try to check at least one of the facts yourself.Due Friday, September 19.ABSTRACT:In April of this year, panelists Roger Pielke, Jr. and Tom Wigley, along with Chris Green, published a paper in the journal Nature arguing that theIntergovernmental Panel on Climate Change (IPCC) underestimated the technicalchallenge of responding to climate change. This forum will present thearguments from this paper and discuss their potential implications for theenergy and climate policies of the next president, regardless of who iselected.PANELISTS INCLUDE:* Roger Pielke, Jr., CIRES Center for Science and Technology PolicyResearch* Tom Wigley, National Center for Atmospheric Research* Frank Laird, Graduate School of International Studies, University ofDenver* Moderator: Carl Koval, CU Renewable and Sustainable Energy InitiativeA few comments from the first homework….0. If you are struggling with the math / units, please check the solutions and also come and see me. 1. Some people did not actually state the total energy consumption of the country. Make sure you specficallyanswer the stated questions.2. Some people used references such as (www.eia.doe.gov). This is too general. The reference should denote the exact document / location.3. Many people cited “Earthtrends”. That is fine. Can someone tell me what “Earthtrends” is?4. If you literally cut and paste text from a reference (even if you give the reference), that is plagiarism. Why?Demonstration with tennis ball and spring…At the beginning, the tennis ball has kinetic energy KE = 0 Joules.After pulling the clip, the tennis ball goes flying across the room with some velocity.Since energy is conserved, where did the energy come from to give the ball this kinetic energy?When the ball finally lands and stops moving, where did the energy go?Our second form of energy is stored energy not associated with any kind of motion.2. Potential EnergyExample – spring potential energy221xkUPE Δ==Where k = spring constant and Δx is the displacement of the spring from its relaxed length.Note that we must have done work (Force x distance) in the first place to store this energy.2Another Example - Gravitational Potential Energywhere m = mass, g = 9.8 m/s2, and h = height above the earth’s surface.mghUPE ==Using a force F we lift a book off the ground by a height h. The work energy is now stored as gravitational potential energy. If we drop the book it accelerated due to gravity, i.e. converting the potential energy into kinetic energy (motion). hFClicker QuestionIf you drop a 12 pound ball a distance of 4 feet, what is the kinetic energy just before it hits the ground?A) 12 JoulesB) 48 JoulesC) 12 foot-poundsD) 48 foot-poundsE) 12 BTUAnother (sometimes useful) unit of energy is the foot-pound.Joules 1.36 pound-foot 1 =400 horsepower and 450 foot-pounds of torqueqV (Voltage) charge) electric(=×==UPEAnother Example - Electrical Potential Energy⎯+eforceCurrent in external circuit3. Chemical Potential EnergyMolecules are formed by binding atoms through sharing of electrons. These molecules often have stored electrical potential energy Æ which we refer to as chemical potential energy.We often free this stored chemical energy through reactions.The amount of stored energy can be surprisingly large!Basketball Cannon Demonstration3Clicker QuestionThis “basketball cannon” demonstration is an example of converting one form of energy into another. Which are the correct energy types?A) Gravitational Potential Energy Æ Kinetic EnergyB) Kinetic Energy Æ Spring Potential EnergyC) Chemical Potential Energy Æ Kinetic EnergyD) Nuclear Energy Æ Chemical Potential EnergyC + O2CO2+ EnergyEnergy comes from re-arrangement of orbital electrons. Note that the nuclei of atoms are not involved (i.e. not a nuclear reaction).Energy appears as the Kinetic Energy of the product(s).Products are “hot” (energy transferred by collisions).Most fossil fuels have stored chemical potential energy !When burning coal, consider the following reaction.C + O2CO2+ EnergyThus, note that for every atom of carbon, we produce one molecule of CO2.This will turn out to be one of the major factors in the increase in carbon dioxide in the atmosphere (a greenhouse


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CU-Boulder PHYS 3070 - Lecture Notes

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