ASTR 115 -Intro to Astronomy. Study Guide for Midterm #2 (3/19/2015)
ASTR 115 -Intro to Astronomy. Study Guide for Midterm #2 (3/19/2015) ASTR 115
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This 9 page Study Guide was uploaded by Eva Malek on Monday March 16, 2015. The Study Guide belongs to ASTR 115 at San Francisco State University taught by Julio Magalhaes in Spring2015. Since its upload, it has received 253 views. For similar materials see Intro to Astronomy in Astronomy at San Francisco State University.
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I had to miss class because of a doctors appointment and these notes were a LIFESAVER
The information in this study guide is very detailed and straight forward. But this could have been a 5 star guide if there were lecture tutorial Examples.
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Date Created: 03/16/15
ASTR 115 Introduction to Astronomy Study Guide for midterm 2 Chapter 4 and 5 Making Sense of Motion in the Universe 1 Describing Motion 0 Speed distance time rate at which an object moves 0 Velocity speed and distance example 10km gr due East 0 Acceleration Change of speed time rate of change of velocity 9Acceleration due to Earth s gravity all falling objects accelerate at the same rate 0 g gravity 98 ms2 speed increases around 10 m s2 for every second falling Galileo s Experiment on Acceleration of Gravity Galileo First scientist who used measurements and experiments to understand nature Dropping different sized objects from Tower of Pisa Objects fall at the same time 9 understand motion 1971 Apollo 15 Astronauts perform same experiment on our airless Moon 2 Changing the Motion of Objects Interaction between objects Force A push or a pull that an object exerts on another object Requires for a change in motion Net force Momentum Mass x velocity Net forces change momentum 9Linear momentum objects moving in a straight line 9Angular momentum rotational momentum of a spinning or orbiting object Mass versus Weight hdass Amount of matter in an object Kilograms Mass is the more basic quantity that affects motion The force of gravity pulling on an object Force pounds newton Weight is proportional to mass Acceleration of gravity on Mars 13 of Earth s 3m s2 Objects in Mars mass would be the same weight would be 13 3 Newton s Laws of Motion Building on Galileo s ideas l Law 1 The Law of Inertia l quotThought Experimentquot What is the natural statequot of motion of an object 9An object at rest will remain at rest and an object in motion will remain in motion at a constant velocity unless it experiences a net external force l Law 2 The Force Law l Fm a net forcemass x acceleration l Law 3 The Interaction Law l Whenever an object exerts a force on a second object the second object exerts an equal and opposite force on the first Forces an interaction between objects Action Forces example tennis racket Reaction Force example tennis ball Friction The motion of a car Tire pushes on Earth Earth pushes back 4 Conservations Laws Express fundamental properties of the Universe Conservation means some quantity remains constant unless exchanged between objects as a result of an interaction 9Conservation of linear momentum total momentum remains the same before and after a collision 9Conservation of Angular Momentum Angular momentum mass X velocity X radius Total angular momentum never changes It can only change by exchanging it with another object Planetary motion example 9 Interprets Kepler s second law equal areas Planet keeps orbiting unless another object comes along to change its angular momentum Earth Distance is longer r diameter is smaller Velocity is V velocity is greater smaller Law of conservation of Energy Energy cannot be created or destroyed it can only be transferred from one object to another or transformed from one type to anther Energy the capacity to create change Forms of energy 9 kinetic energy motion 9Potential energy stored energy 9Radiant energy energy of light 9Thermal energy kinetic energy of the molecules in a substance at a microscopic level temperature Temperature scales Kelvin Celsius Fahrenheit 37515 100 212 27315 0 32 0 27316 45967 Gravitational Potential Energy energy of position in a gravitational field of an object Kinetic energy potential energy constant Higher Kinetic Energy when closer to the sun Earth Higher gravitation Lower grav1tatlonal potentlal energy potentlal energy Newton s Universal Law of Conservation Every object in the universe attracts every other object with a force proportional to both of their masses and inversely proportional to the square if the distance between them Fgravity G M1 X M2 d2 G universal constant M1 mass object 1 M2 mass object 2 d distance between center of objects Gravity Attractive force between any two objects Never goes to zero It s universal 5 The Nature of Light Light forms radio waves microwaves infrared light visible light ultraviolent light Xrays gamma rays ng electromagnetic radiation Fluctuating electric and magnetic fields that travel propagate through space Has both wavelike properties and particle properties All light propagates at the speed of lightquot A light wave Wavelength A 9 distance between the rest Amplitude A 9 quotheight of wavequot related to brightness Frequency f 9Number of crests circles passing a point per second 9 Unit Hertz HZ Cycle second The electromagnetic Spectrum An ordering of the different forms of EM radiation by wavelength All forms of light travel at the same speed THE ELECTRO MAGNETIC SPECTRUM Wavelength niches 39 Radio Microwave Infrared Visible Ultraviolet XR Gamma Ray 39 39 Red light g g a g Violet Light 103 102 105 106 108 1010 1042 Longer Shortest Lower frequency Higher frequency Lower energy Freque fg Higher energy Same Speed Same speed 104 108 1012 l 1015 10396 10398 1020 1 wavelength X frequency speed of light 300 X 108 ms 9Shorter wavelength Higher frequency AWVl Violet light 12 red light 9Longer wavelength lower frequency Light behaves like quotpacketsquot of energy called photons Photons energy depends on frequency of light h Planck s constant f frequency 6 The Nature of Matter Natural occurring chemical elements 98 Atom Cloud of electrons Nucleus protons neutrons 0 0 Electrical forces keep atoms together Negative charges attracted to positive charges Strong Forces Repulsive electrical forces between protons in nucleus require a nuclear fore to hold nucleus together All atoms of one element have the same of protons Atomic number 9 of protons in nucleus 2 Atomic Mass 9 of protons of neutrons He of electrons of protons 400 Isotopes Different version of an element with different of neutrons in the nucleus Some become unstable radioactive parts of nucleus shoots out because its unbalanced Balanced atom electrons protons Molecule electron cloud interaction lead to a bond between two or more atoms Ion Atom that has become electronically unbalanced by loosing or gaining an electron Ion lt gt Ion Electron loss Electron gain 7 The Interaction of Light and Matter Emission Light energy is radiated by matter Absorption Light energy is removed absorbed by matter opaque objects Transmission Light energy travels through an object transparent objects Re ection Scattering matter objects redirect light to another direction EX mirror EX movie screen A red rose re ects red light Objects absorb all the colors but the color they re ect Spreading light into a spectrum spreads light out into its component wavelength Spectrometer A devise for creating and recording a spectrum A Spectrum shows us intensity brightness of light at each wavelength Types of spectra Continuous Continuous variation of intensity from wave line to wave line Usually hot and dense IEmission Line Spectrum MAM Spikes up above continuous Only shows intensity at specific wavelengths Sources that emit this spectra are generally hot and of low density Example Sun during eclipse Absorption line Spectrum Decrease intensity at specific wavelengths superimposed on a continuous spectrum Cold clouds or layers of gas between the observer and a source producing continuous spectrum Example sun 8 Measuring Composition using Light Energy level in Atoms Electron can only exist at specific energy levels Ground state lowest energy level of electron Excited state higher energy levels Energy level transitions only photons with exactly the right amount of energy can cause or result from energy level jumps by electron Emission Line Downward transition of electron emits photons Absorption Line upward transition of electron absorbs photons Chemical Fingerprints each chemical element has a unique spectral fingerprint Alternate visualization of Energy Levels Visualize each energy level as an electron orbit around a nucleus Energy level transitions electron jump between orbits Emission electron jumps downwards between orbits Electron Absorption electron jumps upward between orbitals An emission line spectrum consists of bright lines on a dark background while an absorption line spectrum consists of dark lines on a rainbow background high density diffr39aqion hot matter Q39Ej lmg Continuous spectrum F x a hot gas Emission spectrum 39quot539 cold gas Absorption spectrum n I v u 39 wwwwaa 9 Thermal Radiation Continuous spectrum related to an on object s temperature that is emitted by nearly all dense objects Example sun s thermal radiation spectrum peaks near wavelength of green light visible light Thermal radiation spectrum of a hotter object peaks at a shorter wavelength As temperature goes up peak wavelength goes down Hotter objects emit more light at all wavelength per unit area As temperature if an object increases energy intensity emitted increases Luminosity The total energy per time emitted by an object Higher temperature higher luminosity Size surface area small hot objects can have the same luminosity as a large cool object Doppler shift For a star a Doppler shift is a shift is a shift in the wavelength of spectral lines in an object s spectrum The amount of this shift is a measure of the object s speed toward or away from earth When an object s spectral lines are shifted from their rest wavelengths to longer wavelengths we say that the object s spectrum shows a redshift When the lines are shifted to shorter wavelengths we say that the object s spectrum shows a blue shift A spectrum shows a blue shift when the object is moving toward us and a redshift when it is moving away from us Longer wavelength Shorter wavelength Lower frequency Higher frequency Lower pitch Higher pitch Red shiftecl light Biue shifted ight
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