Gravity Paul Strycker New Mexico State University University of Wisconsin – Platteville 21 December 2010.

GravityGravity

Paul StryckerPaul StryckerNew Mexico State UniversityNew Mexico State University

University of Wisconsin – PlattevilleUniversity of Wisconsin – Platteville21 December 201021 December 2010

Teaching PhilosophyTeaching Philosophy

I want you to learn.I want you to learn.I cannot learn for you.I cannot learn for you.However, I can help you make the However, I can help you make the effort!effort!Therefore, seek help and ask Therefore, seek help and ask questions.questions.


Using your brain helps you learn.Using your brain helps you learn.I cannot use your brain (directly).I cannot use your brain (directly).However, I However, I can can present you with present you with situations that require you to use it!situations that require you to use it!Therefore, take these opportunities.Therefore, take these opportunities.


Today we will use two approaches to Today we will use two approaches to engage your brain:engage your brain:

PredictionPredictionCommunication (speaking and Communication (speaking and listening)listening)

We think before/during/after we We think before/during/after we speak.speak.

We think more carefully about We think more carefully about what is said if we doubt the what is said if we doubt the speaker is trustworthy on the speaker is trustworthy on the subject.subject.

Each table is a team.Each table is a team.Four to a team, if possible.Four to a team, if possible.Rearrange now if necessary.Rearrange now if necessary.

Introduce yourselves!Introduce yourselves!

Assemble Your TeamAssemble Your Team

Have a member Have a member from your team from your team take enough take enough copies for each copies for each person to have person to have one.one.

Review: Forces and AccelerationsReview: Forces and Accelerations

Each case (A-D) Each case (A-D) shows the position shows the position of just one object of just one object at two separate at two separate times.times.


Answer individually first:Answer individually first:

Which situation(s) require a Which situation(s) require a force to act upon the object? force to act upon the object? Why?Why?

Draw the path of each object Draw the path of each object between times 1 and 2.between times 1 and 2.

Does the direction of the force Does the direction of the force and/or acceleration change and/or acceleration change along your paths?along your paths?

In which direction is the In which direction is the acceleration?acceleration?

In which direction is the force?In which direction is the force?


Now agree upon answers as a Now agree upon answers as a team.team.

Answer individually first:Answer individually first:

In which situation(s) could In which situation(s) could gravity be the force gravity be the force responsible?responsible?

If gravity is responsible, then If gravity is responsible, then where would the other object where would the other object be?be?

Is the path of each object still Is the path of each object still reasonable (where gravity is reasonable (where gravity is responsible)? Update it if responsible)? Update it if necessary.necessary.

Does the direction of the force Does the direction of the force and/or acceleration change and/or acceleration change along your paths?along your paths?


Now agree upon answers as a Now agree upon answers as a team.team.

Case ACase A

No No AccelerationAcceleration

No other object is No other object is needed to supply needed to supply a force due to a force due to gravity.gravity.

Case BCase B

AccelerationAcceleration

Case CCase C


Case DCase D


In 1665, Newton began to In 1665, Newton began to wonder if gravity might extend wonder if gravity might extend to the distance of the Moon.to the distance of the Moon.

Orbit Animation

Universal GravitationUniversal Gravitation

http://astro.unl.edu/naap/pos/animations/kepler.html

The acceleration required for the The acceleration required for the Moon is always directed straight Moon is always directed straight toward the Earth.toward the Earth.

This is the same direction as our This is the same direction as our daily experience of acceleration due daily experience of acceleration due to gravity.to gravity.


Our experiences with gravity are very Our experiences with gravity are very limited.limited.

We will never change our distance from We will never change our distance from the center of the Earth by more than the center of the Earth by more than 0.1%.0.1%.

(Lucky astronauts.)(Lucky astronauts.)


If the Sun suddenly collapsed If the Sun suddenly collapsed and became a Black Hole, what and became a Black Hole, what would happen to the orbits of would happen to the orbits of objects in the solar system?objects in the solar system?

(What physical quantities do the (What physical quantities do the force due to gravity depend force due to gravity depend upon?)upon?)

Team Discussion QuestionTeam Discussion Question

The Orbit RaceThe Orbit Race

http://phet.colorado.edu/sims/my-solar-system/my-solar-system_en.html

Start/Finish Start/Finish LineLine

You are currently in a You are currently in a circular orbit.circular orbit.

Choose your initial Choose your initial velocity.velocity.

The first team to orbit The first team to orbit the Earth and cross the the Earth and cross the finish line wins!finish line wins!

200200

11 150150 115115



What was the Winning Strategy?What was the Winning Strategy?

High acceleration was more High acceleration was more important than a high velocity!important than a high velocity!

Orbit Animation

http://astro.unl.edu/naap/pos/animations/kepler.html

Another Orbit RaceAnother Orbit Race

http://phet.colorado.edu/sims/my-solar-system/my-solar-http://phet.colorado.edu/sims/my-solar-system/my-solar-system_en.htmlsystem_en.html

Start/Finish Start/Finish LineLine

Change your initial mass Change your initial mass OROR the mass of the the mass of the Earth. Not both.Earth. Not both.

The first team to orbit The first team to orbit the Earth and cross the the Earth and cross the finish line wins!finish line wins!

200200

11 150150 115115

What was the Winning Strategy?What was the Winning Strategy?

Higher acceleration was achieved Higher acceleration was achieved by increasing the mass.by increasing the mass.

The Universal Law of GravitationThe Universal Law of Gravitation

When did the acceleration increase?When did the acceleration increase?

Force of Gravity Force of Gravity increases with bothincreases with both masses.masses.Force of Gravity decreases with Force of Gravity decreases with distance.distance.

MassMass1 1 and Massand Mass22

Force of Gravity ~Force of Gravity ~ and Distanceand Distance

What will happen to each object?What will happen to each object?

Mass: 1Mass: 1

X-pos: 0X-pos: 0

Mass: 100Mass: 100

X-pos: -X-pos: -200200

Mass: 100Mass: 100

X-pos: X-pos: 200200


Mass: 1Mass: 1

X-pos: 0X-pos: 0

Mass: 100Mass: 100

X-pos: -X-pos: -400400

Mass: 100Mass: 100




What mass will balance the middle bodyWhat mass will balance the middle body

at the start?at the start?

Mass: 1Mass: 1

X-pos: 0X-pos: 0

Mass: 100Mass: 100

X-pos: -X-pos: -400400

Mass: 100Mass: 100



The Universal Law of GravitationThe Universal Law of Gravitation

The distance was doubled.The distance was doubled.By how much did you need to change By how much did you need to change the mass to start the middle body in the mass to start the middle body in balance?balance?

Double? Less? More?Double? Less? More? MassMass1 1 * Mass* Mass22

Force of Gravity = * Force of Gravity = * GG

Distance * DistanceDistance * Distance


Now tie these two Now tie these two together...together...

The Structure of the UniverseThe Structure of the Universe

The structure of the Universe is The structure of the Universe is primarily determined by gravity on all primarily determined by gravity on all scales larger than a few kilometers.scales larger than a few kilometers.




If the Sun suddenly collapsed and became a Black If the Sun suddenly collapsed and became a Black Hole, what would happen to the orbits of objects in Hole, what would happen to the orbits of objects in the solar system?the solar system?

A) Everything in the solar system would continue in A) Everything in the solar system would continue in their original orbits as if nothing had happened.their original orbits as if nothing had happened.

B) Close objects (like Mercury) would fall into the Black B) Close objects (like Mercury) would fall into the Black Hole, but everything else in the solar system would Hole, but everything else in the solar system would not.not.

C) The smaller objects in the solar system (asteroids, C) The smaller objects in the solar system (asteroids, comets, and dust) would fall into the Black Hole, but comets, and dust) would fall into the Black Hole, but the larger objects would not.the larger objects would not.

D) The larger objects in the solar system would fall into D) The larger objects in the solar system would fall into the Black Hole, but the smaller objects would not.the Black Hole, but the smaller objects would not.

E) Everything in the solar system would fall into the E) Everything in the solar system would fall into the Black Hole.Black Hole.

Team Discussion QuestionTeam Discussion Question

Total Eclipse of the MoonTotal Eclipse of the Moon

21 December 2010

Begins at 23:29

Greatest Eclipse at 02:17 (on 22 December)

HomeworkHomework

Gravity Paul Strycker New Mexico State University University of Wisconsin – Platteville 21 December 2010.

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