ASTR 1200 Announcements
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Transcript of ASTR 1200 Announcements
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ASTR 1200Announcements
Websitehttp://casa.colorado.edu/~wcash/APS1200/APS1200.html
..Homework not yet assigned
Lecture Notes going up on the websiteSchedule and text chapters to be added
..
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Explaining the Universe
Science: Model or ExplanationTestCorrectionIterate“Truth” -- All that’s left
Model of the Universe MythMeasurementModern Science
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All That’s Left
Universe Unfolded on Itself in Space and Time
Big Bang and Expanding Universeabout 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 thingsabout the universe. Plus more….
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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 thenfollow what happens.
eg solar system was a gas cloud that collapsed due to gravitySun and Earth formed at same time
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Formation of the Solar SystemUniverse is about 13 Billion Years old (4x1017s)Milky Way 10 Billion Years oldSun 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 DensityShocks 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-SizeBullets into Space
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Lots of Stars
• 100 Billion Stars in Milky Way
• 100 Billion Galaxies in Visible Universe
• Almost an Avagodro’s Number in Universe!
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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
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Question
Why was the Solar System formed from a cloud of gas?
a) The Universe started as diffuse gas
b) Old stars explode to create new gas
c) The galaxy makes new gas that must collapse
d) 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
12
12
tt
xxv
X1 marks position in space at time t1
X2 marks position in space at time t2
Position
VelocityChange of Positionwith time
v1 is velocity at time t1
v2 is velocity at time t2
Acceleration
12
12
tt
vva
Change of Velocitywith 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?
a) 2x107m
b) 5000m
c) 1012m
d) 104m
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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.
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Law #1A 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=ma
a=F/m• Have a mass• Apply a force• Acceleration Results
Note: Law #1 is special case of Law #2 (F=0 a=0)
F = Forcem = massa = acceleration
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Example of Law #2
Push Your Car ---- Large m implies large F to get any a
Let m = 1000kgIf 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)
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Clicker Question
A force of 250 Newtons is applied to a 100kg object. How fast does it accelerate?
a) 2.5m/s/s
b) 25m/s/s
c) 0.4m/s/s
d) 4m/s/s
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Law #3For 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
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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
GravityWeak Nuclear ForceElectromagnetismStrong Nuclear Force
In order of strengthGravity Weakest
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Newton’s Law of Universal Gravitation
221
12 r
mGmF
221
21 r
mGmF
(Law #3 Satisfied)
G = 6.7x10-11 in mks units
Value of G is measured. Nobody knows why it is the value it is.
221
r
eeFe 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) M=6x1024kg. R=6000km
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