Gravity and Orbits Lab for Physics

Phet: Gravity and Orbits In this activity students will be exploring Kepler’s Laws and Orbital Motion using the Gravity and Orbits Phet Simulation. Learning Objectives ● Investigate the shape of planetary orbits ● Relate how planetary orbits link to Kepler’s first two laws of motion. A. Is the orbit of a planet circular? 1. Press the “To Scale” option at the bottom of the screen with the star and planet chosen; 2. Turn on the path/grid option ON; 3. Allow the planet to move through 360 degrees; 4. Measure the horizontal distance from the path line on the left of the star. Write the measurement in the table below. 5. Measure the horizontal distance from the path line on the right of the star. Write the measurement in the table below. Distance (miles) Left side from path to star 94986958.6614 Right side from star to path 91367559.7013 Questions: 1. What do you notice about the distances? ____They differ slightly__________ 2. What does this data say about the orbit of the planet? Please explain. ___This makes the orbit slightly elliptical._________ B. Linking Planetary Orbits to Kepler’s Laws 1. Go to “Model”; 2. Click on sun and planet; 3. Press “play” with path/gravity/velocity/grid ON and leave for one cycle, then “pause”; 4. Please take a screenshot of the trajectory 5. Question: What holds the planet in the orbit? Gravity 6. Question: What shape is the orbit (please use your screenshot to explain this)? As seen in the screenshot, the path is clearly elliptical due to the uneven gridlines. 7. Turn “ON” gravity force button and leave for one cycle, then “pause”; 8. Please take a screenshot of the trajectory. 9. Question: What direction does the force vector face? They are directed at each other. 10.Turn “OFF” gravity force button and leave for one cycle, then “pause”; 11. Please take a screenshot of the trajectory. 12. Question: What happens to the planet? Please explain using your screenshot. It travels in a straight line, as gravity is very much needed. 13.Now increase the velocity of the planet slightly by extending the red “v” arrow of the planet. 14. Question: What happens to the planet in the orbit? The earth travels at a faster rate but it is further away from the sun, this caused my planet to take 590 days to make it around the sun. 15. Question: What is the shape of the orbit when increased? Increasing the velocity makes the path much more elliptical than usual. 16.Now increase the velocity of the planet to a large extent by extending the red “v” arrow of the planet. 17. Question: What happens to the planet in the orbit? The planet went off the screen and never returned to its original point. 18. Question: Now try to explain this in terms of velocity and gravity: The velocity of the planet was too high that it couldn’t remain on track with its orbit due to the speed. 19. Question: Is the velocity constant throughout the journey? Yes, it appeared to be. 20. Question: Which one of Kepler’s Laws does this relate to? Kepler’s 2nd law. 21.With the star and planet chosen and path/grid on, increase the size of the star by sliding the controller to 1.5/1.75/2.0. 22. Question: What do you notice about the orbit? The gravity force is extremely high, and this force causes the earth to move slightly and be put off their path. 23. Question: What happens to the velocity of the path? The velocity is the same with the increased mass as it is with lower mass. 24.Now, do the same thing but change the planet’s mass to 1.5/1.75/2.0. 25. Question: What do you notice about the orbit? It comes to an end due to the increase in mass and force that causes the moon to go directly into the planet.