Physics PhET Lab: A model of a planetary system
Student Learning Objectives:
1. Understand Kepler’s Laws of orbital motion.
2. Discover how does the distance and planet’s tangential speed affect the shape of
the orbit.
3. Measure the change in orbital period as distance is increased.
4. Apply concepts relating to Kepler’s Laws to speculate conditions that lead to a
stable planet environment for evolution of life.
Lab simulation time: 40 minutes
This is a "virtual lab". We will do an experiment using software which can be found at
the PhET simulations page: http:phet.colorado.edu
Find the sim "My Solar System” and run it. You should see this:
0) Play with this simulation and “mouse” around with it. Try to figure out what all the
controls do.
1) Using Select Preset, select “Sun and Planet”. Then select, System centered, Show
Traces, and Show Grid.
a. Describe the shape of the orbit.
2) Measure the distance from the center of the sun to the planet and record in your data
table.
3) Allow the planet to orbit exactly one time around the sun and record the time it took.
4) Now move the planet a little farther out, about 10 more units. Measure the distance
and then record how long it takes for the planet to make one complete orbit. Record this
data.
b. How does the distance and planet tangential speed affect the shape of the orbit?
5) Record the measurements for 8 more points. (8 points)
Distance from the Sun
Time for One Orbit
6) Make a graph of distance (from the star) vs. period of orbit. (5 points each – graph and
two questions, 15 points total)
c. What happens to the period as the star-planet distance increases?
d. Why do you think there is a relationship?
7) Using Select Preset, select “Ellipses”. Run the simulation. Using the farthest planet
Record your observation of planet orbital speed as a function of distance from the sun.
You must measure the distance from the sun and the velocity at each point.
To measure the velocity you must hold our mouse over the planet. You will see two
values that say vx and vy. Record those.
8) You must calculate the velocity at each point. The velocity is the square root of vx
squared plus vy squared. Yes, that is the Pythagorean Theorem.
9) Record the data for 10 trials. (10 points)
Distance from Sun
vx
vy
velocity
10) Make a graph of Sun Distance to velocity for the third planet and answer the
questions. (5 points each – graph and three questions, total 20)
e. What evidence did you gather from this lab to support Kepler’s First Law?
f. What evidence did you gather from this lab to support Kepler’s Second Law?
g. What evidence did you gather from this lab to support Kepler’s Third Law?
(From GVL: slightly edited, points added)