Name: ____________________________ Date: ________________ Period: ________
PhET LAB – Orbital Motion
Part I: Kepler’s Laws – Go to the classroom webpage and click on the link in the link
that says “Kepler’s Laws” (or you can go to http://csep10.phys.utk.edu/astr161/lect/
history/kepler.html).”
1. Scroll about one-fourth of the way down the page to the heading that says,
“Some Properties of Ellipses.” What are the three basic properties of ellipses?
2. How does an ellipse differ from a circle?
3. If planets travel in ellipses around the Sun, why do they appear to make circular
orbits?
4. Scroll down to the next section with the heading, “The Laws of Planetary Motion.”
What is Kepler’s First Law of planetary motion? Include a picture, diagram, or
equation to help you with your explanation.
5. What is Kepler’s Second Law of planetary motion? Include a picture, diagram,
or equation to help you with your explanation.
6. Give an example that helps explain how Kepler’s Second Law affects orbiting
objects.
7. What is Kepler’s Third Law of planetary motion? Include a picture, diagram, or
equation to help you with your explanation.
8. Give an example that helps explain how Kepler’s Third Law affects orbiting
objects
Physics I
Name: ____________________________ Date: ________________ Period: ________
Part I: Build a Solar System – For this part of the lab, go to THE classroom website
and click on the “My Solar System” link. Or go to http://phet.colorado.edu and type “My
Solar System” in the search box. After the page loads click, “Run now.”
9. For the first demo you should have a simple sun-planet system.
a. Click, “start,” and sketch and describe the motion below.
b. What do you notice about the motion of the Sun?
c. Why do you think it moves like this?
d. Does the planet follow a circular or elliptical path (if it is a circular path, the
sun should be in the exact middle of the orbit)?
e. Explain your answer for part d.
f. What do you notice about the velocity of the planet as it orbits the sun
(when does it speed up, when does it slow down, or is it constant through
its entire motion)?
10.
Click “stop” and switch the number of bodies to 3 (bottom left corner). This
should give you a sun-planet-moon system.
a. Click “start” and again, sketch and describe the motion below.
b. Unclick the checkmark that says “show traces.” Explain what the small
object is doing.
c. Which object (or objects) is the Moon orbiting (hint: this is kind of a trick
question)? Explain!!!
Physics I
Name: ____________________________ Date: ________________ Period: ________
d. Turn “traces” back on. Explain why the moon’s path is different on the
right side of the sun, than on the left.
11.
Click “stop” and switch the number of bodies to 4 (bottom left corner). This
should give you a system with a sun, two planets, and moon.
a. Click “start” and again, sketch and describe the motion below.
b. Why do you think the inner planet does not seem to orbit over the same
path?
12.
Click “stop” and switch the number of bodies once again to 2 (bottom left
corner). Also, change the mass of object two to 100.
a. Click “start” and again, sketch and describe the motion below.
b. How is this different than the two object system in #1, and is this?
c. What happens if you change the mass of both objects to 200?
13.
Click “stop” and switch the number of bodies once again to 3 (bottom left
corner). Also, change the mass for both objects two and three to 5.
a. Click “start” and again, sketch and describe the motion below.
b. How is this different from #2, and why is this?
Physics I
Name: ____________________________ Date: ________________ Period: ________
14.
In the upper right hand corner, where it says, “select preset,” click the drop
down arrow and select any of the options that you have not already done in
one of the previous parts. Sketch it below and attempt to explain why the
system behaves as it does.
15.
Write a paragraph explaining how the force of gravity, centripetal
force/circular motion, and orbital motion are related to one another. Think
about all of the previous questions of this lab to help you summarize how all
of these concepts are related.
16.
When you’re done: Switch to four bodies and see if you can make a system
with a sun, planet, and two moons (you might have to play around with the
positions, masses, and velocities). Sketch the system’s motion below and
have me check it to earn extra credit.
Physics I