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

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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.

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)

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At least that’s what people THOUGHT.

Stargazing

• 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

Side Note: Don’t forget Galileo!

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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.

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http://www.windows2universe.org/the_universe/uts/planets.htmlhttp://www.windows2universe.org/the_universe/uts/kepler1.htmlhttp://www.windows2universe.org/the_universe/uts/kepler2.htmlhttp://www.windows2universe.org/the_universe/uts/kepler3.html

At-home reading for the curious.

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 MotionConsider the following:• “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

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http://www.windows2universe.org/physical_science/physics/mechanics/orbit/eccentricity.html

[Briefly review circular motion concepts]

Online Simulationhttp://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.

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Check for Understanding: “Does this animation match-up with your definitions/understanding from our discussions on the previous slide”?

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]

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d

mmGF

We will get some opportunities to work through examples of

this formula!

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Universal Gravitation: GROUP EXAMPLESNecessary (rounded) values: G = 6.7E-11 N·m2/kg2

mE = 6E+24 kg

RE = 6.4E+6 m

mS = 2E+30 kg

1. 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?

2. 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?

3. 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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Special Focus: “Do you know how to put these into your calculator correctly (or use exponent laws)”?

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”?

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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!

Consider theimage to theleft.

What is thisshowing???

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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?!”

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http://www.youtube.com/watch?v=viUhEMNz3Qc

Watch at end of lab:

(Next page shows instructions)

Do on your own at home for edification due to no computers.

Instructions (follow exactly or you will HATE this!)

Open the "Gravity Simulator" programFile --> New (You will see a large red object in the middle of the System)Hit the F9 key

brings up simulator optionsPause the SystemObjects --> Edit Object...

Change the Object's name to EarthSet the Mass to 1 Earth MassSet the Diameter to 1 Earth DiameterChange the Color to what you would like your Earth to beOK

We will assume that the Earth is relatively immobile in our SystemNOTE: 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!

Exponent example: 3.5 x 10^3 is input as 3.5e+3

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Do on your own at home for edification due to no computers.

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

• 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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“Think – Pair – Share”

POEM: Lunacy, by D. LaFazia

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Earth's natural satelliteGives people quite a frightCausing solar eclipses(it sure scared the Gypsies!)

But Earth shows its cold shoulderTo that giant boulderBy blocking the sunlight(day seems just like night!)

Round and round it dancesFurther away it romancesFrom the Earth it does stray(but it won't stay that way!)

Someday when all's said and done

When spinning's had its funThe Moon will not then depart(but rather it will break apart!)

There's more to that lunatic pranceBut leave it to happenstanceI must here this poem end(the Moon is peaking round the bend!)

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.

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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