PhET Activity for MS-ESS1-2: Gravity & Orbits

DIRECTIONS:
1. Click on the 'Model' image button on the left to enter the main simulation.
2. On the right-hand panel, check the boxes for 'Velocity' and 'Path'.
3. At the bottom of the screen, click the 'Play' button to start the simulation.
4. Observe the planet orbiting the star. Notice the green velocity arrow and the blue path that is traced.
5. Explore the playback controls: 'Pause', 'Step Forward', and 'Rewind'.
Spend 2-3 minutes exploring the simulation. Press the different buttons and see what they do. Don't change any of the mass sliders yet. Just get a feel for how the simulation works.

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

DIRECTIONS:
1. Click the 'Reset' button in the top right corner of the screen.
2. On the right-hand panel, check the box for 'Gravity Force'. You should now see blue arrows.
3. Click the 'Play' button and carefully observe the direction of the blue force arrows on both the star and the planet.

QUESTION: What do the blue 'Gravity Force' arrows show about the force between the star and the planet?

DIRECTIONS:
1. Let the simulation run for a few seconds so the planet is partway through its orbit.
2. In the right-hand panel, click the 'off' button for the 'Gravity' control.

QUESTION: Without the force of gravity, the planet no longer moves in an elliptical orbit; instead, it moves in a ___ line tangent to the point in the orbit where gravity was removed. This demonstrates the principle of ___.

(a)  

DIRECTIONS:
1. Click the main reset button (the orange circular arrow in the bottom right corner) to reset the simulation to its default state.
2. On the right-hand panel, make sure 'Path' is checked.

3. 3. Run the simulation and make note of the path of the planet.
   3. Move the 'Star Mass' slider all the way to the right so it is set to '2.0'.
   4. Observe the new orbit.
   
   QUESTION: When the star's mass is doubled, the planet's orbital speed increases, and its orbital path becomes (a)   .

DIRECTIONS:
1. Click the 'Reset' button in the top right corner.
2. Move the 'Star Mass' slider to the left so it is set to '0.5'.
3. Click the 'Play' button and observe the orbit.

QUESTION: What happens to the planet when the star's mass is decreased to half of the sun's mass?

DIRECTIONS:
1. Click the reset button (circular arrow) in the top right corner.
2. Check the 'Path' checkbox.
3. Press 'Play' and let the default orbit draw for a few seconds. Note the shape of the path.
4. Move the 'Planet Mass' slider to the maximum value ('2.0').
5. Observe the new path compared to the old one.

QUESTION: How does changing the planet's mass affect its orbital path? Explain your observation.

DIRECTIONS:
1. Pause the simulation if needed.

2. 2. Click the reset button (circular arrow) in the top right corner.
   3. Check the 'Gravity Force' checkbox in the right side panel.
   4. Click and drag the planet farther away from the star. Observe the blue force arrows.
   5. Now, drag the planet very close to the star. Observe the blue force arrows again.
   
   QUESTION: As the distance between the star and the planet increases, the gravitational force between them...

DIRECTIONS:
1. Ensure you are on the default Sun/Planet screen with the simulation paused and 'Gravity Force' checked.
2. Click the reset button in the top right corner and observe the force when the planet is at its default starting position.
3. Drag the planet to a position very close to the star and observe the force.
4. Drag the planet to a position very far from the star, near the edge of the grid, and observe the force.

QUESTION: Arrange the planet's positions in order from the WEAKEST gravitational force to the STRONGEST.

DIRECTIONS:
1. Click the reset button (circular arrow) in the top right corner.
2. Check the 'Velocity' and 'Path' checkboxes.
3. Click and drag the tip of the green 'Velocity' arrow so towards the planet's body, making the arrow about half its original length but still pointing in the same direction.
4. Click the 'Play' button.

QUESTION: What is the fate of the planet when its initial velocity is significantly reduced?

DIRECTIONS:
1. Click the 'Reset' button in the top right corner.
2. Click and drag the tip of the green 'Velocity' arrow away from the planet's body, making the arrow significantly longer (about twice its original length) but still pointing in the same direction.
3. Click the 'Play' button.

QUESTION: If the planet's initial velocity is too high, it will (a)   .