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CU-Boulder ASTR 1020 - Lecture Notes

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11ASTR 1020 Introductory Astronomy 2: Stars & GalaxiesJanuary 23, 2008Professor Jack BurnsNewcomers - All class info is at website:http://solo.colorado.edu/~jaburns/Astr1020Sp08/index.htmlFiske Planetarium Show: Colorado Skies: Observational Astronomy, Thursday, Jan. 24 at 8:00 pm.2Planetarium• To receive extra credit for attending a Fiske Planetarium show (1 point), you will need to sign your name on a sheet at the end of the show.• Either the ticket-taker or the person doing the show will provide you with access to the sheet.• Fiske shows are free each Thursday night!3Homework • Reading: Chapter 5, sections 5.1, 5.2; summary of key concepts.• MasteringAstronomy Tutorials & Exercises – Scales of the Universe (complete by Jan. 28th). Located at website: http://www.masteringastronomy.com.• Need volunteers for Astronomy in the News on Fridays (please E-mail me).4Astronomy Video of the DayMonty Python’s Scales of the Universe5Today’s Class: Energy and MatterTypes of energyConservation of EnergyGravityMatter: atoms, molecules6Clicker Question from ReadingWhich of the following energy types is also a form of kinetic energy (choose one)?A.) E=mc2B.) Thermal (heat) energyC.) gravitational potential energyD.) Sunlight27Clicker Question from ReadingWhich of the following energy types is also a form of kinetic energy (choose one)?A.) E=mc2B.) Thermal (heat) energyC.) gravitational potential energyD.) Sunlight8Types of energy:1) Kinetic Energy• Movement energy, greater for larger masses, faster movementExamples: rolling, falling, zooming, swinging, etc.91a.) Thermal energy• The “heat energy” of things. A form of kinetic energy, but with random motion. Increasing thermal energy causes atoms to move faster.10Thermal energy measured with an “absolute” temperature scale• T (degrees Celsius) = [T (Fahrenheit) – 32] /1.8.• T in “degrees Kelvin” = Celsius + 273.15 degrees.11Examples:Hot pizza oven450F = ( 450- 32) / 1.8 = 232 C = 505 KRoom temp 70 F = (70-32)/1.8 = 21 C = 294 K ~ 300 K(remember this number)Surface of the Sun = 5000 KInterstellar gas = 10 KAbsolute zero = no thermal energy in matter (all atomic motion stops) = 0 K122.) Potential energy• Energy which has the potential to become kinetic, thermal, or radiative energy. Think of it as stored energy.• Examples: rock on a high ledge (gravitational potential)flashlight battery(electric potential)candy bar (chemical potential)rubber band stretched and held313Mass energy= a special form of potential energyMatter can be thought of as a type of energy and be converted under special situations to energyE = mc2m= mass converted to energyc = speed of lightSince c is large, this means that a tiny amount of matter can release a great deal of energy. Foundation for the Sun’s energy, atom bomb.143) Radiative energy• All types of light:• Sunlight, lamplight• Radio waves• X-rays• Æ MUCH more on this later!15Conservation of Energy• AN IMPORTANT CONCEPT!!!!!!!!!!• Energy can be converted from one type of energy to another, but never created or destroyed• Many actions in the universe represent the conversion of one form of energy to another. Remembering conservation of energy is key to understanding how everything works.16What are Newton’s three laws of motion?Newton’s first law of motion: An object moves at constant velocity unless a net force acts to change its speed or direction.17Newton’s second law of motionForce = mass × acceleration18Newton’s third law of motion:For every force, there is always an equal and opposite reaction force.419What determines the strength of gravity?The Universal Law of Gravitation:1. Every mass attracts every other mass.2. Attraction is directly proportional to the product of their masses.3. Attraction is inversely proportional to the square of the distance between their centers.20Clicker QuestionIf Earth were twice as far from the Sun, the force of gravity attracting Earth to the Sun would bea) Twice as strongb) Half as strongc) One-quarter as strong21Clicker QuestionIf Earth were twice as far from the Sun, the force of gravity attracting Earth to the Sun would bea) Twice as strongb) Half as strongc) One-quarter as


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