PhET Activity for MS-PS2-4: Gravity & Orbits

DIRECTIONS:
1. Click on the 'Model' image button on the left side of the screen.
2. Press the 'Play' button at the bottom center to start the orbit.
3. Observe the planet orbit the star for a few seconds.
4. Press the 'Pause' button to freeze the simulation.
5. Spend 1-2 minutes exploring the checkboxes in the right panel ('Gravity Force', 'Velocity', 'Path', 'Grid') to see what they do.
6. When finished exploring, ensure the checkboxes set as follows: 'Velocity' and 'Path' should be checked, while 'Gravity Force' and 'Grid' should be unchecked.
Get comfortable with the simulation. Press play and pause, and try out the different visual aids in the right panel. No need to change any mass sliders yet. Just explore the basic functions.

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

DIRECTIONS:
1. Click the small 'Reset' button in the top right corner to return the planet to its starting position.
2. In the right panel, click the 'Gravity' switch to the 'Off' position.
3. Press the 'Play' button.

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

DIRECTIONS:
1. Click the orange 'Reset All' button in the bottom right corner to reset the simulation.
2. In the right panel, check the box for 'Gravity Force'.

QUESTION: The blue arrows represent the force of ___. The arrows show that this force is always ___ because they point towards each other.

(a)  

DIRECTIONS:
1. Make sure the simulation is paused at the start with the 'Gravity Force' box checked.
2. In the right panel, find the 'Star Mass' slider.
3. Move the 'Star Mass' slider all the way to the right to its maximum value.
4. Observe the change in the length of the blue force arrows.

QUESTION: Increasing the star's mass causes the gravitational force to (a)   .

DIRECTIONS:
1. Click the small 'Reset' button in the top right corner to reset the Star Mass to its default value.
2. Find the 'Planet Mass' slider in the right panel.
3. Move the 'Planet Mass' slider all the way to the right to its maximum value.
4. Observe the change in the length of the blue force arrows.

QUESTION: Based on your observations in this slide and the previous one, which statement is true?

DIRECTIONS:
1. Ensure the simulation is paused with the 'Planet Mass' slider still at its maximum value from the previous slide.
2. Carefully compare the length of the blue force arrow on the star to the length of the blue force arrow on the planet.

QUESTION: Compare the gravitational force the star exerts on the planet to the force the planet exerts on the star. Are they different or the same? Explain your observation.

DIRECTIONS:
1. Click the small 'Reset' button in the top right corner to reset the planet's mass.
2. Uncheck the 'Gravity Force' box to have a clearer view of the path.

3. 3. Check the 'Velocity' and 'Path' boxes.
   4. Press 'Play' and let the planet complete one full orbit. Notice the shape and speed of the orbit.
   5. Click the small 'Reset' button in the top right corner to reset the planet's position.
   6. In the right panel, move the 'Star Mass' slider to the left, setting it to 0.5.
   7. Press 'Play' and observe the new orbit.
   
   QUESTION: What happens to the planet's orbit when the star's mass is significantly decreased?

DIRECTIONS:
1. Click the orange 'Reset All' button.
2. In the preset panel in the top right, select the 'Earth-Moon' system.
3. Check the box for 'Path' if it is not already checked.
4. Press 'Play' and observe the motion of both the Earth and the Moon.

QUESTION: When observing the Earth-Moon system, you see the Earth 'wobble' slightly as the Moon orbits. What is the best explanation for this?

DIRECTIONS:
1. Press 'Pause'.
2. In the right panel, find the 'Moon Mass' slider and increase it to its maximum value (2.0).
3. Press 'Play' and carefully observe the Earth's motion now.

QUESTION: What happens to the Earth's 'wobble' when the Moon's mass is increased?

DIRECTIONS:
1. In the top right panel of presets, select the 'Earth-Satellite' system.
2. Check the box for 'Gravity Force'.
3. Press 'Play' and let the satellite begin to orbit.
4. Press 'Pause'.

QUESTION: A satellite stays in orbit because the force of gravity provides a constant pull (a)   the Earth, balancing the satellite's forward motion.