Gravity and Orbits
Answer all questions in complete sentences, in your own words. You may not copy another
student’s answer, even if you are working together.
Open Internet Explorer. Type in the following address:
o http://phet.colorado.edu/en/simulation/gravity-and-orbits
Click the green “Run Now” button.
Spend a few minutes familiarizing yourself with the simulation.
Click Reset All to return the simulation to the preset values. Turn on the “Gravity Force”,
“Velocity”, and “Path.”. Press play.
1. What direction is the Earth’s velocity?
2. What direction is the Earth’s gravitational force?
3. What direction is the Sun’s gravitational force?
4. Increase the planet’s mass. Describe any changes that occur.
Click reset. Press play and allow the planet to make one revolution. Now, increase the
Sun’s mass and allow the planet to make another full revolution.
5. Describe any changes in the planet’s gravitational force, velocity, and orbital shape.
6. What happens to the gravitational force as the distance between the Sun and planet
decreases?
7. What happens to the planet’s velocity as the distance from the Sun decreases?
Click reset. Turn “Velocity” off. At the top, click the button that shows the Sun, Earth
and Moon. Click play.
8. Describe the Moon’s path. Why does the Moon’s path look like this?
9. What gravitational forces are acting on the Moon?
Click Reset All to return the simulation to the preset values. Turn on the “Gravity Force”,
“Velocity”, and “Path”. Press play.
10. Allow the Earth to make a full revolution. At some point in the second revolution, turn
gravity off. Describe what happens. What direction does the Earth travel? What happens to
the gravitational force?
11. State Newton’s Law of Universal Gravitation. Write a paragraph explaining how this
simulation demonstrates this law.