PhET Activity for MS-PS2-1: Gravity & Orbits

DIRECTIONS:
1. Click on the 'Model' image on the center-left of the screen to enter the simulation.
2. In the panel on the right, check the boxes for 'Path' and 'Grid'.
3. At the bottom of the screen, press the blue 'Play' button to start the simulation.
4. Observe the planet orbiting the star. Press the 'Pause' button, and then the 'Rewind' button to reset the simulation.
Spend 2-3 minutes exploring the simulation. Press play and pause. Use the rewind button. See what the different presets in the top-right menu do. Do not change any 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 selected.
2. Press the small 'Reset' button in the top right corner to reset the system.
3. In the right-hand panel, check the box for 'Gravity Force'.
4. Press 'Play' and observe the blue force arrows.

QUESTION: Based on Newton's Third Law, which statement accurately describes the gravitational forces shown by the blue arrows?

DIRECTIONS:
1. Ensure you are in the 'Model' tab with the 'Sun and Planet' preset selected.
2. Press the small 'Reset' button in the top right corner.
3. In the right-hand panel, move the 'Star Mass' slider to the maximum value (2.0).
4. Press 'Play' and observe the planet's new orbit.

QUESTION: When the star's mass is doubled, the gravitational force becomes ___ and the planet's orbital path becomes ___.

(a)  

DIRECTIONS:
1. Do not reset the simulation from the previous slide.
2. In the right-hand panel, move the 'Star Mass' slider to the minimum value (0.5).
3. Press 'Play' and observe the planet's path.

QUESTION: What happens to the planet when the star's mass is reduced to its minimum value?

DIRECTIONS:
1. Press the small 'Reset' button in the top right corner.
2. Click and drag the planet to a position that is about half as far from the star as its original position.
4. Press 'Play' and observe the new orbit.

QUESTION: As the planet's orbital distance from the star increases, its orbital period (the time to complete one orbit) (a)   .

DIRECTIONS:
1. Press the small 'Reset' button in the top right corner.
2. In the right-hand panel, toggle the 'Gravity' switch to 'Off'.
3. Ensure the 'Velocity' checkbox is checked.
4. Press 'Play'.

QUESTION: Explain why the planet moves in a straight line when gravity is turned off. What physics principle does this demonstrate?

DIRECTIONS:
1. Press the small 'Reset' button in the top right corner.
2. Toggle the 'Gravity' switch back to 'On'.
3. From the preset menu in the top-right corner, select 'Sun, Planet and Moon'.
4. Press 'Play' and observe the force vectors.

QUESTION: Which forces are acting on the Moon in this system?

DIRECTIONS:
1. Select the 'Plant, Moon' preset.
2. Set the 'Moon Mass' slider to its maximum value (2.0).
4. Press 'Play' and carefully observe the motion of the PLANET.

QUESTION: When the moon's mass is significantly increased, what do you observe about the planet's motion and why?

DIRECTIONS:
1. Switch to the 'To Scale' tab at the bottom with the 'Earth and Satellite' preset.

2. 2. Check the 'Gravity Force,' 'Velocity,' and 'Path' boxes.
   3. Click and drag the tip of the satellite's green velocity vector to make it about half of its original length.
   4. Press 'Play' and observe the satellite's path.
   
   QUESTION: If a satellite's initial velocity is too ___, it will be unable to counteract Earth's ___ and will crash.

DIRECTIONS:
1. Press the small 'Reset' button in the top right corner.
2. Click and drag the tip of the satellite's green velocity vector to make it significantly longer than its original length.
3. Press 'Play' and observe the satellite's path.

QUESTION: When the satellite's initial velocity is high enough, it achieves 'escape velocity' and its path becomes a(n) (a)   .