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ASTR 1200 Announcements

ASTR 1200 Announcements. Homework not yet assigned Lecture Notes going up on the website Schedule and text chapters to be added. Website http://casa.colorado.edu/~wcash/APS1200/APS1200.html. Explaining the Universe. Science: Model or Explanation Test Correction Iterate

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ASTR 1200 Announcements

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  1. ASTR 1200Announcements .. Homework not yet assigned Lecture Notes going up on the websiteSchedule and text chapters to be added .. Website http://casa.colorado.edu/~wcash/APS1200/APS1200.html

  2. Explaining the Universe Science: Model or Explanation Test Correction Iterate “Truth” -- All that’s left Model of the Universe Myth Measurement Modern Science

  3. All That’s Left Universe Unfolded on Itself in Space and Time Big Bang and Expanding Universe about 13 Billion Years ago Formed Galaxies from gas Formed Stars and Planets Earth & Sun about 4.6 Billion Years Old In this course we will explain why we think these things about the universe. Plus more….

  4. Question:Why Are Our Atoms Arranged this Way? e.g. Why are our atoms on a planet, not in a black hole? HISTORY IS DESTINY Make assumption about initial state of matter and then follow what happens. eg solar system was a gas cloud that collapsed due to gravity Sun and Earth formed at same time

  5. Formation of the Solar System Universe is about 13 Billion Years old (4x1017s) Milky Way 10 Billion Years old Sun and Planets – 4.6 Billion Years old Sun has done about 25 orbits of Milky Way Stars are being formed all the time -- some young, some old Stars are formed from clouds of gas

  6. Starts as Thin Cloud Ensuing High Density Shocks Is Site of Collapse Spins Up Like Ice Skater

  7. Swirling Gas Falls into “Disk Stability” 99.9% Ended in Sun (0.1% in Jupiter) Probably the Same Around All Stars -- Planets are Common Shoots Planet-Size Bullets into Space

  8. Lots of Stars • 100 Billion Stars in Milky Way • 100 Billion Galaxies in Visible Universe • Almost an Avagodro’s Number in Universe!

  9. Catastrophe Theory • Theory In Vogue When I was in Grade School – (1950’s ouch!) • Two Stars Stray Near Each Other • Close Orbit Pulled Gas from Sun • Gas Formed Planets • Predicts Planets Very Rare (Collisions Rare) • Astronomy Advanced Hugely in 20th Century

  10. Question Why was the Solar System formed from a cloud of gas? • The Universe started as diffuse gas • Old stars explode to create new gas • The galaxy makes new gas that must collapse • Stars never collide so they cannot form solar systems

  11. Galileo • First Great Modern Scientist • Quantitative Analysis • Tenacious Pursuit of Truth • Challenged Aristotle and Church • Used Telescopes to Demolish Old Solar System View • Persecuted In Italy – Celebrated Elsewhere

  12. Isaac Newton (1643-1727) • Greatest Scientist of All Time • Quantitative Prediction • Mechanics, Optics, Math – Theory & Observation Two Basic Concepts Mass – Amount of Matter (Not Weight) Inertia – Tendency of Objects to Have Unchanged Motion

  13. Motion • x = v * t • v = a * t • x = ½ * a * t2

  14. Motion X1 marks position in space at time t1 X2 marks position in space at time t2 Position Change of Position with time Velocity v1 is velocity at time t1 v2 is velocity at time t2 Acceleration Change of Velocity with time

  15. Question A spaceship accelerates from rest at 20gees (200m/s/s) steadily for 1.2 days (105 seconds). How far has it travelled? • 2x107m • 5000m • 1012m • 104m

  16. Newton’s Laws • Law #1: A body at rest or in motion remains that way unless acted upon by an outside force. • Law #2: a=F/m • Law #3: For every action there is an equal and opposite reaction.

  17. Law #1 A body in motion remains that way unless acted upon by an outside force. No Forces Contact Forces (electrical) Gravity

  18. Law #2 F = Force m = mass a = acceleration F=ma • Have a mass • Apply a force • Acceleration Results a=F/m Note: Law #1 is special case of Law #2 (F=0 a=0)

  19. Example of Law #2 Push Your Car ---- Large m implies large F to get any a Let m = 1000kg If you apply 20N (Newtons is the unit of force) a=20/1000=.02m/s2 ---- accelerates .02m/s for every second you push Push for 10 seconds --- car will be moving .02m/sx10s= 0.2m/s (if on ice so no friction) (friction is yet another force)

  20. Clicker Question A force of 250 Newtons is applied to a 100kg object. How fast does it accelerate? • 2.5m/s/s • 25m/s/s • 0.4m/s/s • 4m/s/s

  21. Law #3 For every action there is an equal and opposite reaction. For every ma there is an equal and opposite ma. Big one doesn’t move much Equal Mass Implies Equal Acceleration

  22. But What is F? a=F/m not enough because we don’t know what F is. Need a new law to describe forces There are Four KNOWN Forces Gravity Weak Nuclear Force Electromagnetism Strong Nuclear Force In order of strength Gravity Weakest

  23. Newton’s Law of Universal Gravitation (Law #3 Satisfied) G = 6.7x10-11 in mks units Value of G is measured. Nobody knows why it is the value it is. Electrical Force Equation Similar

  24. Clicker Question What is the weight of a 100kg person standing on the surface of the Earth. (in Newtons) M=6x1024kg. R=6000km a) 6.7x1021N b) 1.6x108N c) 1000N d) 6.7x10-3N

  25. But What is a Force? Newtons Laws Give Value, and Show what to do. Force is an Exchange of Virtual Particles

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