ASTR 1200 Announcements

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ASTR 1200Announcements
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Homework not yet assigned Lecture Notes going up
on the websiteSchedule and text chapters to be
added
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Website http//casa.colorado.edu/wcash/APS1200/AP
S1200.html
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Explaining the Universe
Science Model or Explanation Test Correction
Iterate Truth -- All thats left
Model of the Universe Myth Measurement Moder
n Science
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All Thats 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.
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QuestionWhy 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
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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
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Starts as Thin Cloud
Ensuing High Density Shocks Is Site of
Collapse Spins Up Like Ice Skater
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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
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Lots of Stars

• 100 Billion Stars in Milky Way
• 100 Billion Galaxies in Visible Universe
• Almost an Avagodros Number in Universe!

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Catastrophe Theory

• Theory In Vogue When I was in Grade School
  (1950s 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

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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

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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

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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
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Motion

• x v t
• v a t
• x ½ a t2

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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
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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

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Newtons Laws

• Law 1 A body at rest or in motion remains that
  way unless acted upon by an outside force.
• Law 2 aF/m
• Law 3 For every action there is an equal and
  opposite reaction.

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Law 1
A body in motion remains that way unless acted
upon by an outside force.
No Forces
Contact Forces (electrical)
Gravity
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Law 2
F Force m mass a acceleration
Fma

• Have a mass
• Apply a force
• Acceleration Results

aF/m
Note Law 1 is special case of Law 2 (F0
a0)
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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) a20/1000.02m/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)
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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

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Law 3
For every action there is an equal and opposite
reaction.
For every ma there is an equal and opposite ma.
Big one doesnt move much
Equal Mass Implies Equal Acceleration
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But What is F?
aF/m not enough because we dont 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
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Newtons 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
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Clicker Question

• What is the weight of a 100kg person standing on
  the surface of the Earth. (in Newtons)
  M6x1024kg. R6000km
• a) 6.7x1021N
• b) 1.6x108N
• c) 1000N
• d) 6.7x10-3N

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