Name ___Tom Jones____ Gravitational Lab
Go to HYPERLINK "http://phet.colorado.edu/simulations/sims.php?sim=My_Solar_System" http://phet.colorado.edu/simulations/sims.php?sim=My_Solar_System and click on Run Now.

1. Move the slider all the way to accurate, click on the tape measure and the grid.

2. Click the radio button for 4 objects and run the simulation until the purple planet (body 2) has made one complete orbit (one year).
3. After the first orbit (year), turn off the traces (show traces box) and watch another orbit (year) of the purple planet (body 2).
Question One: Is blue moon (body 3) circling the yellow sun (body 1) or the purple planet (body 2)? Explain your answer.

The blue moon is circling the purple planet, because it is constantly in that planets orbit. The purple planet though is circling the yellow sun making it seem almost like the blue planet is circling it as well.
4. Increase the mass of the sun (body 1) to 400 and allow the simulation to run for one complete orbit of the purple planet (body 2).

5. Decrease the mass of the sun (body 1) to 175 and allow the simulation to run for one complete orbit of the purple planet (body 2). (~90 seconds)
Question Two: How do the orbits of the planets change when the mass of the sun is increased or decreased? Why? Explain your answer.

Wen the mass is 400, the planets will circle the sun much closer, because it has a much stronger gravitational force due to its large mass compared to the smaller planets. When the mass is smaller, the radius that the planets circle is much bigger because there is less gravitational force on them, and they circle the sun at a much slower speed.

Question Three: Why does the sun (body 1) follow a circular path? How does the path change as its mass changes? Why? Explain your answer.