Conceptual Physics

http://mrlafazia.com/PHYS111/lessons/201011Fall/PHYS111_22.ppt

TUESDAY November 9th, 2010LESSON GOALS:

• Complete Earth-Moon gravity simulation• Share thoughts on gravity Discussion Prompt • Calculate Earth-Moon gravitational force magnitude• Watch 1-minute clip on The Matter Disk (SOLAR SYSTEM EVOLUTION)

• Partner-Switch Discussion activity• Practice use of Newton’s Law of Universal Gravitation• Quick Quiz on “N’s LofUG”

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Gravity Simulator: Part 2• Making our OWN Earth-Moon system

– We have already found the following…• Size (in kilometers) (meaning Diameter)• Mass (in kilograms)• Semi-Major Axis (in kilometers) (relates to distance from Earth)• Eccentricity (how “elliptical” its orbit is)• Inclination (where it is in relation to the Earth’s equator)

– “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?!”

• MAKE PREDICTION and THEN test it.

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Discussion Prompt: gravityMYTH BUSTIN’!

“It is often a misconception that other planets do not have gravity of their own. Think about space exploration. How would other planets NOT “having” gravity make space travel MORE DIFFICULT”?

Think about this individually (make some notes for your own reference) and then we will share our ideas and discuss.

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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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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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Universal Gravitation: PRACTICE PROBLEMSNecessary (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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Quick Quiz: Uni. Grav.

• (Your notes must be away, as usual). • Show your work (and final answer) for this use

of Newton’s Law of Universal Gravitation:

“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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Recommended Reading:

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• p. 105, Sections 6.1 – 6.5, 6.7 – 6.11

Note: The text does not offer much specific help on Earth and Space topics, so we will rely mostly on outside sources for our references for the majority of this unit.

Looking Ahead:

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• Next class we will be looking at the Earth Science aspect of our Earth & Space unit.