Transcript Lesson 16x - MrLaFazia.com

PHY111: Summer 201253
Lesson 16: Space Science Tie-ins
-
Planetary Motion
Anatomy of an Orbit
Universal Gravitation
The Earth-Moon System
The Big Bang
Solar System Evolution
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A Brief History of Planetary
Motion
There is no reason to write these down… I will simply talk you
through them, briefly, and if you have any questions we can
discuss those. You will have them to review at any time by
accessing this lesson online.
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The old old days…
• Ancient Greece
– Things rose or fell according to what they were
• Smoke rises (cousin to clouds!)
• Objects fall (made from earth!)
• Gave birth to the terms
– Levity (lightweight)
– Gravity (heavy)
At least that’s
what people
THOUGHT.
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Stargazing
Side Note: Don’t forget Galileo!
• Always the popular past time, early humans noticed
that celestial bodies moved in regular patterns
– Planet = “wanderer”
• Tycho Brahe (1546-1601)
– Extremely detailed measurements of planetary motion
– Built first observatory (an entire island!)
– Had precise instruments constructed
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Johannes Kepler
• One of Brahe’s assistants and a brilliant
mathematician
• Used heliocentric (sun-centered) model and Brahe’s
measurements to discover basic descriptions for the
behavior of every planet and satellite (moons,
comets, etc.)
– “fatal” blow to church-enforced geocentric description
– Verified Copernicus’ ideas
• Those 3 descriptions are now known as Kepler’s 3
laws of planetary motion.
http://www.windows2universe.org/the_universe/uts/planets.html
http://www.windows2universe.org/the_universe/uts/kepler1.html
http://www.windows2universe.org/the_universe/uts/kepler2.html
http://www.windows2universe.org/the_universe/uts/kepler3.html
 At-home
reading for
the curious.
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The falling apple
• About 45 years after Kepler
– Isaac Newton saw an apple fall, and also observed
the moon in the daytime sky
– What’s keeping the moon from flying off into
space?
– Force that makes the apple fall must be causing
the moon to continually “fall” toward Earth
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A universal force
• He named this force gravity, and he said it
existed between every single object!
• The amount of force depends on:
– How massive the objects are
• More mass = more force
– The distance between the objects
• Closer together = more force
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Newton vs. Einstein:
clash of the titans!
• Newton said that gravitational forces
permeated instantly…
– Suppose the sun disappeared…
• Einstein said that gravitational effects would
take time to feel
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Einstein’s Ideas
• Gravity is not a force, but a “bend” in space
• More massive bodies will cause a greater bend
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Planetary Motion
review circular
Consider the following: [Briefly
motion concepts]
• “How is it related to circular motion”?
• Describing planetary motion
– Orbit, revolution; rotation definitions
• What force causes this circular motion?
• Does it truly follow a circular orbit?
– Ellipse definition (more vs. less eccentric orbits)
• “How does the motion change (and why) along
an orbit”?
• Perihelion and aphelion definitions
http://www.windows2universe.org/physical_science/physics/mechanics/orbit/eccentricity.html
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Online Simulation
http://www.windows2universe.org/physical_science/physics/mechanics/orbit
/perihelion_aphelion.html
The above simulation gives a very simple
but exacting view of the difference
between what occurs at the perihelion
and aphelion of an orbit.
Check for Understanding: “Does this animation match-up
with your definitions/understanding from our discussions on
the previous slide”?
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Law of Universal Gravitation
• m1 and m2 = masses of two objects
• d = distance between objects’ centers of mass
• G = universal gravitational constant
G is … 6.7 x 10-11 [N·m2/kg2]
m1m2
F G 2
d
We will get some
opportunities to work
through examples of
this formula!
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Universal Gravitation: GROUP EXAMPLES
Necessary (rounded) values: G = 6.7E-11 N·m2/kg2
mE = 6E+24 kg
RE = 6.4E+6 m
mS = 2E+30 kg
1.
2.
3.
Special Focus: “Do you
know how to put these
into your calculator
correctly (or use
exponent laws)”?
A certain ant has a mass of 0.000003 kg. This ant is walking in tunnels
an insignificant distance beneath the surface of the Earth. What is the
ant’s Weight on the Earth?
A full trash can of mass 25 kg has a radius of 0.45 m. A sanitary engineer
of mass 100 kg has a radius of 0.30 m. Facing the trashcan, the edge of
the sanitary engineer’s stomach is 2.3 m away from the edge of the
trashcan directly in front of him. What magnitude (value) of
gravitational Force attracts the two?
Mercury has a mass of 3.3E+23 kg. It has a semi-major axis value of
about 5.8E+10 m. With what force-value does the Sun attract Mercury?
Also, with what force-value does Mercury attract the Sun?
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Try it with a partner!: Uni. Grav.
“The mass of a certain planet is 2x1020 kg. The
planet has a diameter of 6x105 m. How much
does a person weigh on the surface of this
planet if they have a mass of 75 kg”?
CHALLENGE: Show their weight if you use Newton’s 2nd Law of Motion, instead, if
the acceleration due to gravity for the planet is g=0.15 m/s2!
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Consider the
image to the
left.
What is this
showing???
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• The purpose of this exercise is to create our own Earth-Moon
system and analyze the relationship between the Earth (Terra)
and our nearest celestial neighbor, Luna.
– “What effect does the Earth have on the Moon”?
– “What effect does the Moon have on the Earth”?
– “How long does it take the Moon to complete its orbit”?
• “Does this make sense”??
– “What happens when we delete the Earth?!”
(Next page shows instructions)
Do on your own at home for
edification due to no computers.
Watch at end of lab:
http://www.yout
ube.com/watch?
v=viUhEMNz3Qc
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Instructions (follow exactly or you will HATE this!)
Exponent example: 3.5 x 10^3 is input as 3.5e+3
Open the "Gravity Simulator" program
File --> New (You will see a large red object in the middle of the System)
Hit the F9 key
brings up simulator options
Do on your own at home for
Pause the System
edification due to no computers.
Objects --> Edit Object...
Change the Object's name to Earth
Set the Mass to 1 Earth Mass
Set the Diameter to 1 Earth Diameter
Change the Color to what you would like your Earth to be
OK
We will assume that the Earth is relatively immobile in our System
NOTE: You will have to unpause the simulation in order to see your changes. Repause once the Earth shows back up. Minimizing the screen
during a pause will also make the screen go blank. Unpause and Repause to refresh the screen, as needed.
Objects --> Create Objects...
Make sure that the Reference Object is set to the Earth (naturally)
Color the moon some appropriate color (grey, for instance)
Use your reference sources (if your computer is internet-ready this task will be easier) to find the following properties for the Moon:
SIZE: _____________ km (this means “Diameter”)
MASS: _____________ kg
Semi-Major Axis: ______________ km
Eccentricity: _____________
Inclination: _____________ (to “Ecliptic”)
Fill in the properties, using the appropriate units. Leave the other parameters at their default settings!
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Calculation: Earth-Moon attraction
• Using Newton’s Law of Universal Gravitation,
work out the gravitational force acting
between the Earth and the Moon.
– “Does it matter which object’s ‘Point of View’ you
consider”?
• WHY or WHY NOT?
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The Big Bang
• Research in Small Groups: “What is the Big
Bang Theory and what does it propose”?
– “How does this relate to the idea of Energy
Conservation”?
– “Is there just one version of the Big Bang Theory”?
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Video Segments: The Big Bang
• Segment 1: Theory Behind the Big Bang (3 mins)
• Segment 2: Evidence for the Big Bang (6 mins)
• Segment 3: Replicating the Big Bang (3 mins)
– These clips will be uploaded to Blackboard along with this lesson.
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Solar System Evolution: The Matter Disk
“Think – Pair – Share”
•
•
•
Watch the 1-minute clip on the Matter Disk (may review a few times, with
comments…watch with no lights on, as it is not a crisp image).
Partner-Switch Discussion: After we have watched the 1-minute clip (a few
times, perhaps, since it’s so fast), consider your own detailed responses to the
following questions:
– “Does it make sense to you that the matter that makes up our Solar
System could at one time have been dust and gas”?
– “Does it make sense to you that gravity could pull these swirling gases
together”?
– “Does it make sense to you that individual planets could form in this
process”?
– “Does it make sense to you that our Sun would have over 98% of the
matter from this matter disk”?
– “Does it make sense that the Sun could become the Sun (as in, begin the
process of Fusion)”?
Discuss the answers to these questions in pairs. Then, I will have you switch
to another partner and share what you discussed before reviewing.
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POEM: Lunacy, by D. LaFazia
Earth's natural satellite
Gives people quite a fright
Causing solar eclipses
(it sure scared the Gypsies!)
Someday when all's said and done
When spinning's had its fun
The Moon will not then depart
(but rather it will break apart!)
But Earth shows its cold shoulder
To that giant boulder
By blocking the sunlight
(day seems just like night!)
There's more to that lunatic prance
But leave it to happenstance
I must here this poem end
(the Moon is peaking round the bend!)
Round and round it dances
Further away it romances
From the Earth it does stray
(but it won't stay that way!)
Goodnight
Now share your own poems! Submit copies of these to me and I will “web publish”
them as examples. Let me know if you want to show up as “Anonymous” or if you
want credit for the poem.
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Grades/Assignments:
You (or you and your partner) will be reciting your end of
semester poem!
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Looking Ahead:
Lesson 17 is our last class (Wednesday is allowed for continued
work on the take home Test III). Keep an eye out for
announcements—I will post the Test soon.
Do not forget to complete the Course Evaluations in Banner!
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