PhET Activity for MS-ESS1-1: Gravity & Orbits

DIRECTIONS:
1. You should be on the initial screen with two options: 'Model' and 'To Scale'. Click on the 'Model' image on the left side of the screen.
2. You are now in the 'Model' tab with the 'Sun and Planet' preset. Observe the central star and the orbiting planet.
3. In the control panel on the right, check the boxes for 'Velocity', 'Gravity Force', 'Path', and 'Grid'.
4. At the bottom of the screen, locate the Play/Pause button and the simulation speed controls.
5. Press the play button to start the simulation and observe the planet's motion.
Spend 2-3 minutes exploring the simulation. Press play and pause. Use the speed controls to see the simulation run faster or slower. Click the reset button (circular arrow in the top-right panel) to see how it works. Do not change the mass sliders yet.

QUESTION: Are you acquainted with the tools in this simulation?

DIRECTIONS:
1. Ensure you are in the 'Model' tab with the 'Sun and Planet' preset.
2. Click the reset button (circular arrow in the top-right panel).
3. Make sure the 'Gravity Force' checkbox on the right panel is checked. You should see blue arrows on the star and planet.
4. Press the play button and observe the direction of the blue force arrows as the planet orbits.

QUESTION: What do the blue arrows represent, and what is their effect on the planet?

DIRECTIONS:
1. Start in the 'Model' tab with the 'Sun and Planet' preset. Click the reset button (circular arrow in the top-right panel).

2. Ensure the 'Gravity Force' and 'Path' checkboxes are selected.
3. Press play and let the planet complete one orbit to see the default path.
4. While the simulation is running, use the 'Star Mass' slider in the bottom-right panel to increase the mass to its maximum value (2.0).
5. Observe the change in the size of the force arrows and the planet's new path.

QUESTION: When the star's mass is increased, the gravitational force ___ and the planet is pulled into a ___ orbit.

(a)  

DIRECTIONS:
1. Click the reset button (circular arrow in the top-right panel).
2. Press play and observe the default orbit.
3. While the simulation is running, use the 'Planet Mass' slider to change its mass from 'Earth' to maximum (2.0).
4. Carefully observe the planet's orbital path.

QUESTION: Changing the planet's mass has a (a)   effect on its orbital path.

DIRECTIONS:
1. Click the reset button (circular arrow in the top-right panel).
2. Set the 'Star Mass' slider to its minimum value (0.5).
3. Set the 'Planet Mass' slider to its maximum value (2.0).
4. Make sure 'Path' is checked. Press play.
5. Observe the motion of the star.

QUESTION: Describe what you observe about the star's motion when its mass is low and the planet's mass is high. Why do you think this happens?

DIRECTIONS:
1. Click the reset button (circular arrow in the top-right panel).
2. Make sure the simulation is paused. The green velocity vector should be visible on the planet.
3. Experiment by clicking and dragging the head of the green velocity vector to make it shorter or longer before pressing play.
4. Reset the simulation after each trial to test a new velocity.

QUESTION: Match the change in initial velocity to the resulting orbital outcome.

DIRECTIONS:
1. Click the reset button (circular arrow in the top-right panel).
2. Press play and let the planet travel for a few seconds.
3. While the planet is moving, turn gravity off using the 'Gravity' toggle switch in the right-hand panel.

QUESTION: What happens to the planet's motion when gravity is turned off?

DIRECTIONS:
1. Click the reset button (circular arrow in the top-right panel).
2. Choose the 'Sun, Planet, Moon' preset.
3. Make sure the 'Gravity Force' and 'Path' checkboxes are checked.
4. Press play and observe the motions and forces on all three bodies.

QUESTION: In the 'Sun, Planet, Moon' system, which bodies exert a significant gravitational force on the MOON?

DIRECTIONS:
1. Click the reset button (circular arrow in the top-right panel).
2. Use the 'Slow' simulation speed control in the bottom-left corner.
3. Press play and carefully watch the path of the moon relative to the planet, and the path of the planet relative to the sun.

QUESTION: The moon orbits the ___, and the entire planet-moon system orbits the ___.

(a)  

DIRECTIONS:
1. Remain in the 'Model' tab with the 'Sun, Planet, Moon' preset.
2. Press play and pause the simulation repeatedly.
3. Try to pause the simulation at the exact moment when the moon is directly between the sun and the planet.

QUESTION: For a person on the planet to experience a solar eclipse, the celestial bodies must be aligned in a specific order. Reorder the following bodies from the light source to the observer.