This document is a lab assignment on gravitation and Kepler's laws. It includes an introduction to universal gravitation and Newton's law of gravitation. The document contains a procedure where students are asked to use an online simulation to observe gravitational force between two objects at different distances and masses. They then calculate the gravitational constant, G, and compare it to published values. Several conclusion questions follow about gravitational forces and Kepler's laws of planetary motion.

1. Lab 05 – Gravitation and Keplers Laws Name:
_____________________
Why everyone in this class is attracted to everyone else.
https://phet.colorado.edu/en/simulation/gravity-force-lab
Adapted from Chris Bier’s Collisions PhET Lab OPTION
A: CREATIVE COMMONS - ATTRIBUTION
Introduction:
Every object around you is attracted to you. In fact, every
object in the galaxy is attracted to every other object in the
galaxy. Newton postulated and Cavendish confirmed that all
objects with mass are attracted to all other objects with mass by
a force that is proportional to their masses and inversely
proportional to the square of the distance between the objects'
centers. This relationship became Newton's Law of Universal
Gravitation. In this simulation, you will look at two massive
objects and their gravitational force between them to observe G,
the constant of universal gravity that Cavendish investigated.
Important Formulas:
Procedure: https://phet.colorado.edu/en/simulation/gravity-
force-lab
1. Take some time and familiarize yourself with the simulation.
Notice how forces change as mass changes and as distance
changes.
2. Fill out the chart below for the two objects at various

2. distances.
3. Rearranging the equation for Force, you can CALCULATE
the value of G using the values given below for m1, m2, and d,
and the value for the Force that you obtain in the simulation.
Record the force between the two object and then solve
(calculate G) for the universal gravitation constant, G and
compare it to values published in books, online, or your text
book. The numbers you calculate for G will vary slightly from
row to row. Remember significant digits!15 pts
Mass Object 1 Mass Object 2 Distance
Force Gravitation Constant,G
50.00 kg
25.00 kg
3.0m
50.00 kg
25.00 kg
4.0m
50.00 kg
25.00 kg
5.0m
50.00 kg
25.00 kg
6.0m
50.00 kg
25.00 kg
9.0m

3. What do you notice about the force that acts on each object? 3
pts
[Answer Here]
Average value of G: _________________2 ptsUnits of G:
_______________2 pts
Published value of G: ________________2 pts Source:
_______________2 pts
How did your average value of G compare to the published
value for G that you found? 3 pts
[Answer Here]
Conclusion Questions and Calculations:Bold and Underlinethe
correct answer to each question.
1. Gravitational force is always attractive / repulsive. (circle) 2
pts
2. Newton’s 3rd Law tells us that if a gravitational force exists
between two objects, one very massive and one less massive,
then the force on the less massive object will be greater than /
equal to / less than the force on the more massive object. 2 pts
3. The distance between masses is measured from their edges
between them / from their centers / from the edge of one to the
center of the other. 2 pts
4. As the distance between masses decreases, force increases /
decreases. 2 pts
5. Doubling the mass of both masses would result in a change of
force between the masses of 4x / 2x / no change / ½x / ¼x. 2
pts
6. Reducing the distance between two masses to half while

4. doubling the mass of one of the masses would result in a change
of force between the masses of 8x / 4x / no change / ½x / ¼x. 2
pts
7. What is the gravitational force between two students, Dylan
and Sarah, if Dylan has a mass of 75 kg, Sarah has a mass of 54
kg, and their centers are separated by a distance of .45 m? 2 pts
________________ N
8. What is the gravitational force between two students, John
and Mike, if John has a mass of 81 kg, Mike has a mass of 93
kg, and their centers are separated by a distance of .62 m? 2 pts
________________ N
9. Imagine a 4820 kg satellite in a geosynchronous orbit. If an
85 kg piece of space junk floats by at a distance of 3.5 m, what
force will the space junk feel? 2 pts
________________ N
10. With what acceleration will the space junk move toward the
satellite? 2 pts ______________ m/s2
11. With what acceleration will the satellite move (if any)? 2
pts ______________ m/s2
12. The gravitational force on the moon by the earth. 2 pts
________________ N
13. The gravitational force on the earth by the moon. 2 pts
________________ N
Show your calculation for 12 and 13 here.
The lab is continued on the next page.
Follow the directions carefully before answering the following

5. questions.
Click http://phet.colorado.edu/en/simulation/gravity-and-orbits
and Run Now
1) Run the Simulation, Keep all the default settings, but select
the Earth and Satellite option. Turn on all of the options in the
“Show” menu, then run and play with the simulation for a
while. Which is experiencing a greater gravitational force: The
satellite or the earth? 3 pts
[Answer Here]
2) Pause the Simulation. Hit “Reset”. (not “Reset All”). Alter
the mass of the Satellite. Does the mass of the satellite have
any impact on its Orbit? Explain. 3 pts
[Answer Here]
3) Pause the Simulation. Hit “Reset.” Click and drag the “v” at
the end of the red velocity in order to decrease the satellite’s
velocity.
a. What happens when you hit play? Why? 3 pts
[Answer Here]
b. Why doesn’t this happen to satellites normally? 3 pts
[Answer Here]
4) Pause the Simulation. Hit “Reset.” Click and drag to
increase the satellite’s velocity. What happens when you hit
play? Why? 3 pts
[Answer Here]
5) Pause the Simulation. Hit “Reset.” Click and drag the

6. satellite itself to move it further away from earth. What
happens when you hit play? Why? 3 pts
[Answer Here]
6) Try to create another stable orbit that is further or closer to
earth. What other very important variable would you need to
alter with this new orbit? 3 pts
[Answer Here]
7) Just for fun. Click and drag earth to create a very small
velocity for earth. Can the satellite still orbit a moving planet?
3 pts
[Answer Here]
8) Pause the Simulation. Hit “Reset.” On the top left tabs,
change your view so that you are to scale. In the Show menu,
you can now also turn on the “Tape Measure”. Run the
simulation, with the path shown.
How far out is the satellite? 3 pts
[Answer Here]
How long does it take for the satellite to orbit earth? 3 pts
[Answer Here]
9) Switch modes, so that you are now looking at just the earth
and the moon.
How far is the moon? 3 pts

7. [Answer Here]
How long does it take for the moon to orbit the earth? 3 pts
[Answer Here]
10) Again Switch modes, so that you are now looking at just
the earth and the sun.
How far is the earth from the sun? 3 pts
[Answer Here]
How long does it take for the earth to orbit the sun? 3 pts
[Answer Here]
11)
According to Kepler’s third law, the time it takes for one
complete orbit is proportional to the mean distance between the
centers of two bodies. T2 ≈ r3. When a constant is included,
the equation is . Use the adjustable mass controls on the
simulation of just the earth and sun to determine what mass the
“m” in Kepler’s equation must refer to. Is it the mass of the
orbiting object or the mass of the central object?
12) Kepler actually proposed three laws.
Kepler’s Laws of Planetary Motion
First Law: Each planet travels in an elliptical orbit around the
sun, and the sun is at one of the focal points.
Second Law: An imaginary line drawn from the sun to any
planet sweeps out equal areas in equal time intervals.
Third Law: The square of a planet’s orbital period (T2) is

8. proportional to the cube of the average distance (r3) between
the planet and the sun, or T2 r3.
An Illustration of Keplers 1st and 2nd Laws is Shown here:
A1=A2. In this case you can see that when a planet is closer to
the sun then it must cover more distance in the same time. It
must move faster.
Reset all. Select the Earth and Sun. Choose to show only the
path and velocities. Manipulate the Simulation until you
achieve an elliptical orbit. The speed of the earth increases
slightly as it orbits closer to the sun but decreases slightly when
it is further from the sun. (hint: move the sun itself.) Do a print
screen. Then paste it below into this document. 8 pts
Page 1 of 5
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8999
I don’t think one step is more important than any of the others.
Without one of the steps, the others won’t succeed. If I had to
pick one phase over the others where I would place special
emphasis, it would be the analysis phase. You can do all the
planning and investigating you want, and then assemble the
system. But if you don’t take the time to see if what you are
planning is actually what you need, you could waste a lot of
time and money. When you look at how a system functions, and
the role of the systems analyst, according to Stair and Reynolds
(2014), everything flows through the systems analyst. So in
design, analysis is probably one of the major keys to success.
A system is a series of procedures and routines that are
designed to carry out a function. A system can also be a set of
specific equipment, each with its own design and function, that
come together to perform as a set. To develop a system, there
must be an outlined purpose for the system which involves
figuring out a purpose driven design. Once the system is
created, it must be worked and tested to refine the results. Any
shortcomings are identified and fixed, and the final product is
implemented and maintained.

10. 9000
A system is a program designed to help process data or
complete tasks. There are generally 5 steps to developing new
software investigation, analysis, design implementation and
maintenance and review (Ralph Stair and George Reynolds,
2014). In the investigation phase the purpose for the new system
must be defined and determined if it is worth undertaking. This
stage is where the brainstorming occurs to determine what
outputs are needed and what inputs will be required. The second
phase is analysis where, how the program will solve the
problem is determined.
Next would be the design phase, here we see the
process by which the input will be looked at and processed to
create the desired outputs. The fourth phase is implementation.
In this phase the completed system is compiled and the training
of the users is key to the success of the new software. The final
and most important phase is maintenance and review. Even the
best programmers will miss bugs or miss-intemperate the
desired outcomes. With maintenance and review these bugs will
be caught by the users, the programmers can fix them and
update the system to fix these problems.
9001
Even though piracy has resulted in massive losses of revenue in
the entertainment and software industry, it has created many
jobs designed to combat it. I think it is a question of one's
ethics. Let me present an analogy, piracy is similar to buying a
book and photocopying it and passing it out to friends. The
seller still received the money for the book, but missed out on
the possibility of selling more books. It isn't as cut and dry as
stealing. On the other hand, identity theft is blatantly wrong
and often highlights the worst acts humanity is capable of
committing.
"A rapidly growing area of identity theft involves child

11. identity theft..." (Stair & Reynolds, 2014) This crime is more
than just finding a new way into someone's wallet. Identity
theft is extremely personal and can be devastating to one's
personal finances and credit. To combat this increasingly
popular crime, many banks provide new theft protection policies
and have implemented better technology to reduce risk.
9002
Piracy directly affects the profitability of companies and
software piracy is a direct blow to the software industry. Piracy
can be described as the copying or the unauthorized use of
another person’s or company’s work. This directly takes the
flow money from the developer and in turn reducing the ability
for further growth, development and any possibility of lowering
cost of the software. There are also many risks involved in
using pirated software and a few are: increased risk of exposure
to a virus, being subject to fines for copyright infringement, and
the risk of potential public and private embarrassment. I don’t
know anyone who has had their identity stolen but I have had
my identity stolen in 2005 while I was in boot camp. As a result
of this, someone graciously gave $25,000 of debt as a present
for graduation. For a long time I never knew the importance of
computer security and I my home computer networked through
my house to be able control many things with my cellphone.
One day my neighbor called me and said I should really think
about strengthening the security of my network and he started
turning things on an off in the house from across the street.
That was a valuable lesson for me because at that point almost
anyone with a small amount of common sense would have been
able to download an app that is available on the android market
that searches and cracks Wi-Fi passwords for users to steal
internet.