http://ww.chabotcollege.edu/faculty/shildreth/astronomy/gravity2017.html

Chabot College - Scott Hildreth

Exploring Gravity vs. Magnetism Survey 

You can't blame gravity for falling in love. - Albert Einstein
 



This assignment has THREE things to do:

1) Complete a short survey yourself in Part A: Exploration, answering the five questions about orbits, gravity, and magnetism.  Record your own answers, and read the actual answers available below, so you will be able to explain those answers to others!

2) Then, ask 2-3 friends or family members to complete the same survey, and then explain the correct answers to them. The questions alone (as a separate handout or online page) are accessible at: http://www.chabotcollege.edu/faculty/shildreth/astronomy/gravityqs.html.   Please record:

(a) who you gave the survey to, 

(b) what level of school they have completed,

(c) their answers, verbatim (Try to resist telling them whether they are right or wrong while they did the survey- instead just state that you need their opinions for your research.)

(d) their reactions when you explained the correct answers,  and

(e) what you had to do to explain the correct answers, especially to the first question about orbits!  This is the most important part of the assignment, so spend some time here.  Most people do better when you actually SHOW them a magnet and try the experiment with a refrigerator.    Did you have to build a model? Show them the answers?   Did they believe you?  Which question did they have the hardest time understanding?

3) Finally, evaluate at least one of the resources listed in Part B: Research below, and share your review in a short paragraph. Don't forget the citation!

Please remember to TYPE your answers, and print a copy double-spaced and spell-checked; aim for at least 250 words (about 1 page is fine), with citations for any outside references used.

On-line classes: Please POST your assignment on Canvas in the discussion forum directly, not as an attachment.

On-campus classes
:
  Please POST your assignment on Canvas if you are absent from class  by the due date, but please then bring your work on paper to the next class so that I can grade it!  I won't grade the work submitted on Canvas.     


Part A:  Exploration

Step 1 -- Starting Out: Why Are Astronauts Floating?

This is the most important question!  Take a look at one or more of the following images:

Bruce McCandless, NASA Astronaut, flying untethered from the Space Shuttle, in 1984. (http://apod.nasa.gov/apod/ap050322.html)

STS-121 Crew in the Shuttle (http://www.nasa.gov/images/content/152384main_s121e07024_lo.jpg)

Space Station Astronauts (https://www.youtube.com/watch?v=8v9ObEVaNZo)  (sorry for the ads - this is a YouTube issue..) 

Astronauts Floating Weightless (https://www.youtube.com/watch?v=VDu9z4SCTmc)

Now what is your answer to this question? 

1. Space shuttle astronauts in orbit around Earth seem to be floating inside (or outside!) their spacecraft because (choose the ONE best answer):

a) there is no force of gravity on them

b) the force of gravity on them is much less than it is on Earth

c) they are falling, and so is their spacecraft around them

d) the Earth's magnetic field supports them and their spacecraft

e) they are massless in space

f) they are closer to the Moon, and the Moon's gravity is actually helping to keep them suspended.

Record your answer.... We'll find out the correct response in just a bit!




Step 2 of the Survey! -- Exploring Newton's Law of Gravity

 

Decide which object will create a larger gravitational force on you!  Check your answers as you go!

 

2)  The force of gravity on you from a pound of lead compared with the force from a pound of feathers?

a) The force from lead will be larger than the force from feathers.

b) The force from feathers will be larger than the force from lead.

c) The forces will be the same.


3) The force of gravity on you from a pound of liquid water, compared with the force from a pound of solid ice, compared with the force from a pound of gaseous water vapor?

a) The force from liquid water will be largest.

b) The force from solid ice will be largest.

c) The force from gaseous water vapor will be largest.

d) The forces will be the same.


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4) The force of gravity on you from a pound of sugar, in the form of a solid sugar cube, a small, dense, compressed sugar pill, or a large ball of spun cotton candy.

a) A solid sugar cube will have the largest force.

b) A compressed sugar pill will have the largest force.

c) A ball of spun cotton candy will have the largest force.

d) The forces will be the same.

 

 


Step 3 of the Survey! -- Exploring Gravity vs. Magnetism

5. For the following questions, consider a standard sized small refrigerator magnet. Decide whether each statement is TRUE or FALSE.  Check your answers as you go!

 True or False?
 Statement
Answer!
 

The force of magnetism decreases with distance.

 
 

While touching the refrigerator, the magnetic force on the magnet (from the refrigerator) is stronger than gravitational force (from the Earth)

 
 

When held a fraction of an inch (a few millimeters) away from the refrigerator, so that the magnet is not touching, the magnetic force on the magnet (from the refrigerator) is stronger than gravitational force (from the Earth).

 
 

When held a few inches (about 10 centimeters) away from the refrigerator, so that the magnet is not touching, the magnetic force on the magnet (from the refrigerator) is stronger than gravitational force (from the Earth).

 
 


Magnetism can effectively be ignored a short distance away.


 
 


Gravity can effectively be ignored a short distance away.

 
 


Magnetism depends on the type of materials involved.


 
 


Gravity depends on the type of materials involved.


 


Part B: Research!

Please read and/or explore one (or more) of the following articles and websites.  In a short paragraph, summarize what you learned from the article, and share your thoughts on whether it was a resource you would use to teach others about gravity.  Remember the full citation is expected and required for credit.  Remember too how you can demonstrate your good scholarship in your writing (refer to the handout!)

You are also welcome to explore other media sites that involve gravity, including OK Go's incredible video from 2016, Upside Down & Inside Out, available to watch on YouTube: https://www.youtube.com/watch?v=LWGJA9i18Co , or something about the "Vomit Comet" (google it!)

And if you wish, explore fiction that involves black holes or gravity!  A nice reference to books and stories using black holes is available online from Foothill College professor Andy Fraknoi:

Fraknoi, A. (Oct. 2015) Science Fiction Stories with Good Astronomy & Physics: A Topical Index. Astronomical Society of the Pacific.  https://www.astrosociety.org/education/astronomy-resource-guides/science-fiction-stories-with-good-astronomy-physics-a-topical-index/#black




Background Information and Answers Below!

 

 









Background to Exploring Gravity:  The law of gravity is given by a single equation, first shared by Isaac Newton in 1687:


FG
is the force of attraction between the two objects.


m1
is the mass of one of the objects - basically a count of the number of protons, neutrons, and electrons

m2 is the mass of the other object.

r is the distance (separation) between the centers of mass of each object.

 

 In the equation above, G is the universal gravitational constant.  It is basically a "conversion factor" to adjust the number and units so they come out to the correct value.  This is a universal constant so it is true everywhere, on Earth, on Pluto, on Alpha Centauri, and in the most distant galaxies that we can see.  The value of this constant is incredibly small:


In the units for "G", the "N" refers to Newtons, a unit of FORCE; "m" refers to meters, a unit of length, and "kg" refers to kilograms, a unit of mass. 
The exponent "10-11 means that the number really would be written as 0.000 000 000 067 (which is very small! )
 

So what does gravity depend upon?  Just the 3 variables you see:  The mass of one object, the mass of another, and the distance between those two objects. 


And what doesn't gravity depend upon?  Do you see anything about temperature?  Or motion of either object?  Or the type of matter?  Or its shape?  Gravity doesn't depend on ANY of these factors.

More detailed answers to the Chabot College
Exploring Gravity vs. Magnetism Survey

Part 1:

1.  Space shuttle astronauts in orbit around Earth seem to be floating because:

False: a) there is no force of gravity on them

Not so! There is gravity is space, and gravity still exerts an attractive force on objects in a vacuum.  Gravity cannot be shielded nor canceled, and so astronauts still feel a force of gravity from Earth. They would still feel a force if they were at the moon, even though that force would be much less.  Check out: https://www.youtube.com/watch?v=iQOHRKKNNLQ originally from Catalyst, produced by the Australian Broadcasting Service from 2012, for a good video to explore.  (Cite this if you use it in your report!).

False: b) the force of gravity on them is much less than it is on Earth

Not so! The shuttle operates just 250-350 nautical miles above the Earth's surface, and so is only about 5-8% farther from the center of the Earth than we are on the planet's surface. The force of gravity is a bit less - perhaps 95% as much.

True c) they are falling and their space craft is falling around them

This is an answer most people have a hard time understanding!  In some sense, Shuttle astronauts are like parachutists in free-fall. The only major difference between the shuttle astronauts and parachutists is that the shuttle is moving fast enough "sideways" around the Earth (at 17,000 miles per hour or so) so that, as they fall, the Earth actually curves away underneath them.

They fall continuously in a "controlled orbit."  Take a look at this YouTube video response from the BBC about orbits. (http://www.youtube.com/watch?v=YxRCyokN3g8&feature=related)

If you have children, the NASA Kid Science Network clip is one very short start at this concept they might enjoy. (
https://www.youtube.com/watch?v=UwqQCxPuVmc)

They might also enjoy: CoconutScienceLab (13 October 2013). Weightless Astronaut Pushes Herself With a Single Hair | NASA ISS Space Science HD https://www.youtube.com/watch?v=WMK36dpHIkg

False: d) the Earth's magnetic field supports them and their spacecraft

Not so: from the refrigerator magnet, you know that the force of magnetism, while powerful, does not extend for tremendous distances with the power to levitate large objects like the Shuttle.

False: e) they are massless in space

Not so: there is no way to eliminate the mass of the shuttle nor astronauts.  They still are made up of protons, neutrons, and electrons!  And mass is just the measure of those fundamental particles.

False: f) they are closer to the Moon, and the Moon's gravity is actually helping to keep them suspended.

Not so: At 4,300 miles or so from the Earth's center, the Shuttle is still almost 240,000 miles from the Moon! The force of gravity from Earth is still MUCH larger.


 

Part 2:

2.  The force of gravity on you from a pound of lead compared with the force from a pound of feathers
?

Gravity doesn't depend upon the TYPE of matter, just how many protons, neutrons, and electrons are present.  You can mix up those protons and neutrons and electrons into different types of atoms; some could be carbon with just six protons, neutrons, and electrons (as would be present in organic materials like feathers!)  Other atoms could be lead, with 82 protons and electrons, and around 124-126 neutrons.  But however you combine them, each proton has the same mass, and so does each neutron or electron. 

A pound is a unit of force, representing how much gravitational force is present on a certain amount of material (composed of those protons, neutrons, and electrons)  While a pound of lead might not take up as much space as a pound of feathers, and not require as many lead atoms as would be found in a pound of feathers, both would weigh the same (a pound!), and both represent the same total gravitational force on the same total number of protons, neutrons, and electrons.

3. The force of gravity on you from a pound of liquid water, compared with the force from a pound of solid ice, compared with the force from a pound of gaseous water vapor?

Gravity doesn't depend upon the STATE of matter (solid, liquid, or gas).  It only depends upon how MUCH matter there is.  For a pound of whatever substance you have, in whatever state it is in (and whatever temperature it might be, or how fast it is moving!), there are still the same number of protons, neutrons, and electrons, and the gravitational force will be the same.  Yes, the water vapor (steam!) would "float" and be more challenging to weigh, but it still weighs something! 

4. The force of gravity on you from a pound of sugar, in the form of a solid sugar cube, a small, dense, compressed sugar pill, or a large ball of spun cotton candy.

Gravity doesn't depend upon the DENSITY of matter either; whether atoms and molecules are tightly packed, loosely packed, or free to roam around, they still have the same numbers of protons, neutrons, and electrons!


Part 3

5. Consider a standard refrigerator magnet.

True The force of magnetism decreases with distance.

You can see this simply by noticing that the magnet is strongly attracted to the refrigerator when close, but farther away, it no longer feels a strong enough force to make it leap across space and attach itself to the refrigerator.  You can "feel" this with your hand holding the magnet, too - near to something metallic, magnets will feel strongly attracted; farther away the force will be less.

True While touching the refrigerator, the magnetic force on the magnet (from the refrigerator) is stronger than gravitational force (from the Earth).

The forces acting on the magnet include gravity and magnetism, but since the magnet does not fall, magnetism must be stronger here.

True  When held a fraction of an inch (a few millimeters) away from the refrigerator, so that the magnet is not touching, the magnetic force on the magnet (from the refrigerator) is stronger than gravitational force (from the Earth).

Once you let the magnet go, it is still pulled onto the refrigerator's metal surface rather than falling to the ground. Magnetism is a strong force if the distance between objects is smaller than the distance between a magnet's two poles (North and South).

False When held a few inches (about 10 centimeters) away from the refrigerator, so that the magnet is not touching, the magnetic force on the magnet (from the refrigerator) is stronger than gravitational force (from the Earth).

Since the magnet now falls to Earth at this distance, gravity's force must now be stronger than the magnetic attraction between the refrigerator and object. Note that the mass of the magnet does not change, and its distance from the center of Earth doesn't, so the gravitational force on the magnet is constant throughout your experiment. So it must be that the magnetic force is getting much weaker with distance.

True Magnetism can effectively be ignored a short distance away.

As the above experiment shows, just a few centimeters away from a surface, the magnetic force somehow has dropped substantially. But why is magnetism so short-ranged?  The key is that magnets have two opposite poles, and close to either one, the electrons in a metal will feel a significant force. But from some distance away the poles effectively shield each other, and "cancel out."

False Gravity can effectively be ignored a short distance away.

As far as we understand today, gravity is a universal attractive force, with no possible way to shield it, reverse it, or cancel it. In this, gravity is extremely different than magnetism.  At the greatest distances in the universe, gravity still exists.

True Magnetism depends on the type of materials involved.

Compare wood and metal! You can also add here that magnetism depends on the motion of charges; in the centers of planets like Jupiter or Saturn, the hot liquid hydrogen in rapid rotation as the planets spin creates enormous spinning currents which generate the large magnetic fields those planets have. But remember that magnetism won't hold onto moons or rings! It is gravity that acts at greater distances, holding on to all matter.

False Gravity depends on the type of materials involved.

Examine the universal law of gravity to notice that there is absolutely no dependence on the type of matter involved (solid, liquid, gas), nor on its shape nor composition. The key is simply how much matter is involved; a kilogram of lead, a kilogram of water, and a kilogram of air would all generate and respond to the same gravitational force.


 9/18 - SH
 

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