In Orbit. Overview. Venn Diagram Positioning. Time Required. Materials Required. Newton s Laws of Motion: In Orbit [ 1 ]

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1 In Orbit Overview The celestial bodies of our solar system move according to rules governed by gravity, Newton s Laws of Motion, and mathematics. In this computer-based simulation developed by the University of Colorado, students have the opportunity to experiment with a limited number of variables that impact the movement of planets around a star. By manipulating the mass of objects and their velocities, students can observe the changes in elliptical motion of these objects relative to their gravitational foci. These variables add up to the challenges and outcomes in launching an object into orbit. Newton s Laws of Motion: First law: An object at rest remains at rest unless acted on by a force. An object in motion will remain in motion with the same velocity unless acted upon by a force. Second law: Force acting on a mass produces acceleration. The greater the mass of an object, the greater the amount of force is required to accelerate the object. Venn Diagram Positioning Space Science Mathematics Physical Science Time Required 90 minutes Materials Required A computer connected to the Internet per student/ group Third law: For every action, there is an equal and opposite reaction. In Orbit [ 1 ]

2 Background & Connection to the ISS Newton s Laws of Motion are at the heart of so many physical forces that we experience on Earth. Though we are not as close to the illustrations of those Laws as expressed in orbiting bodies, orbits are tangible for students. Moreover, the International Space Station is an excellent opportunity to introduce and investigate Newton s Laws of Motion via orbits. The ISS weighs nearly one million pounds and is essentially free falling around Earth. The primary force that keeps the ISS from falling to Earth or leaving orbit is the gravitational force of Earth. Its orbital path maximizes energy efficiency to keep the ISS from crashing to the Earth s surface or leaving the Earth s atmosphere and drifting off into space. Standards Addressed Most objects in the solar system are in regular and predictable motion. Those motions explain such phenomena as the day, the year, phases of the moon, and eclipses. Gravity is the force that keeps planets in orbit around the sun and governs the rest of the motion in the solar system. Gravity alone holds us to the Earth s surface and explains the phenomena of the tides. The Earth is the third planet from the sun in a system that includes the moon, the sun, eight other planets and their moons, and smaller objects, such as asteroids and comets. The sun, an average star, is the central and largest body in the solar system. In Orbit [ 2 ]

3 Activity Steps Inquiry 1. Prompt students to think about what they already know about orbits/orbiting. Ask questions such as: Why do we have 365 days in a year? (Why is there a leap year every four years?) It takes approximately 365 days (365 and ¼ days, thus a leap year) for the Earth to orbit the sun. Why does the moon s cycle between full moons/new moons take approximately 28 days? It takes approximately 28 days (27.3 days) for the moon to orbit the Earth. How do satellites travel (or stay) in space? They orbit the Earth from varying altitudes. 2. Whether it s through discussion or through writing, students should arrive at the common thread among the questions is orbiting. Ensure that students have at least a rudimentary understanding of the concept of orbiting. 3. Share the multimedia definition of orbit on the CASIS Academy microsite [www. casisacademy.org]. Additionally, the multimedia definitions for microgravity and satellites help illustrate aspects of orbiting and Newton s Laws of Motion. 4. As a transition into the main part of the lesson, ask students how we figured out that satellites could orbit the Earth, or even perhaps how Newton was able to develop his ideas around motion long before we launched vehicles into space. Students should be able to articulate that it was through observing orbits in our solar system that it s orbiting that keeps the universe organized and functioning. This lesson is a chance to delve deeper into that idea. Investigate & Manipulate 5. Divide students into small groups, so that each group has access to a computer with Internet access. (Note: you may want to divide students earlier so their groups can view the multimedia definition(s) in Step 3 above.) 6. Guide students through the following experience on this website: colorado.edu/en/simulation/my-solar-system Click Run Now unless you re able to download it. Move the slider all the way to accurate, click on the tape measure and the grid. (mid/lower right of interface) Click the radio button for 4 objects (lower left of interface) and run the simulation until the purple planet (body 2) has made one complete orbit (one year). (Students need to click Stop.) After the first orbit (year), turn off the traces (deselect Show Traces box) and watch another orbit (year) of the purple planet (body 2). 7. Pose the following question to students (have them answer aloud or write it down): Is blue moon (body 3) circling the yellow sun (body 1) or the purple planet (body 2)? Explain your answer. In Orbit [ 3 ]

4 8. Now on the website, prompt students to: Increase the mass of the sun (body 1) to 400 and allow the simulation to run for one complete orbit of the purple planet (body 2). Decrease the mass of the sun (body 1) to 175 and allow the simulation to run for one complete orbit of the purple planet (body 2). (~90 seconds) 9. Pose the following questions to students (have them answer aloud or write it down): How do the orbits of the planets change when the mass of the sun is increased or decreased? Why? Explain your answer. Why does the sun (body 1) follow a circular path? How does the path change as its mass changes? Why? Explain your answer. 10. Have students continue manipulating data on the website and answering questions: Choose the preset for Sun and Planet from the pull-down menu. Complete the data table below by changing the mass as shown and recording the length of the year in seconds, and also measuring the distance from the planet to the sun at the closest point (perihelion) and farthest point (aphelion). (Make sure slider is set to most accurate) Mass of Sun (body 1) Mass of Planet (body 2) Closest Distance to Sun (perihelion) Farthest Distance to Sun (aphelion) In Orbit [ 4 ]

5 Q: When is the planet moving fastest? Why? Q: What makes the length of the year increase and decrease? Why? Q: A planet in a circular orbit would always be the same distance from the sun. What do you notice about orbits with the shortest years? Why? Choose the ellipses preset from the pull-down menu. You may move the slider bar about 2/3 of the way towards fast for this simulation. Run the simulation until the green planet (body 4) returns to its starting point (one planetary year) Planet Closest Distance to Sun (perihelion) Farthest Distance to Sun (aphelion) Purple Planet (body 2) Blue Planet (body 3) Green Planet (body 4) Change the y velocity of the blue planet (body 3) to 90 and the green planet (body 4) to 70. Run the simulation again until the green planet (body 4) returns to its starting point (one planetary year) Planet Closest Distance to Sun (perihelion) Farthest Distance to Sun (aphelion) Purple Planet (body 2) Blue Planet (body 3) Green Planet (body 4) estimate Q: How does the year of a planet closer to the sun compare with one that is farther away? Why? Q: How can an orbit be made more circular? Explain your answer. Q: In your own words describe what an orbit is and what factors affect the size, speed and time (period) of an orbit. In Orbit [ 5 ]

6 Extensions & Modifications Give students the opportunity to have a more open-ended experience in which they use this web resource to manipulate data and try to detect patterns or seeming anomalies. Extend the lesson into language arts by having students write explanatory essays that teach readers about orbits/orbiting. To abridge the lesson, you can complete the online prompts and manipulation as a class on your smart board. Your familiarity with the website and with the steps should greatly speed up the process. Attribution Adapted from Chris Cochran s Orbits-Effects of Mass and Distance, In Orbit [ 6 ]

7 Orbit! Or Is a Bit too Confusing? The Earth orbits the sun every 365 days. Technically, it s every 365 and ¼ days that s why we have a Leap Year every for years to make up for that quarter day. The moon orbits the Earth roughly every 28 days (27.3 to be exact). Gravity is the key to those orbits. Thanks to gravity, smaller bodies are attracted to larger bodies. The Earth orbits the sun because the sun is much bigger, so its gravitational pull keeps us in its orbit. Our moon orbits the Earth because our home planet is much bigger than the moon, so the Earth s gravitational pull keeps it in orbit. Of course, the International Space Station also orbits the Earth (along with hundreds and hundreds of other satellites.) The same forces help keep the ISS in orbit. In this activity, you re going to go to a website where you can manipulate the forces that affect orbits by changing the size of the objects or the velocity of the orbiting object. Don t worry. It ll make more sense when you go to the site. Speaking of 1. Go to this website: Click Run Now unless it s already downloaded. Move the slider all the way to accurate, click on the tape measure and the grid. (mid/lower right on screen) Click the radio button for 4 objects (lower left on screen) and run the simulation until the purple planet (body 2) has made one complete orbit (one year). (Click Stop.) After the first orbit (year), turn off the traces (deselect Show Traces box) and watch another orbit (year) of the purple planet (body 2). 2. Answer this question: Is blue moon (body 3) circling the yellow sun (body 1) or the purple planet (body 2)? Explain your answer. 3. Now on the website: Increase the mass of the sun (body 1) to 400 and allow the simulation to run for one complete orbit of the purple planet (body 2). Decrease the mass of the sun (body 1) to 175 and allow the simulation to run for one complete orbit of the purple planet (body 2). (approximately 90 seconds) 4. Now, do your best to answer these questions: How do the orbits of the planets change when the mass of the sun is increased or decreased? Why? Explain your answer. Why does the sun (body 1) follow a circular path? How does the path change as its mass changes? Why? Explain your answer. In Orbit [ 7 ]

8 5. Now that you have a good feel for what to do, continue to manipulate data on the website and answering questions: Choose the preset for Sun and Planet from the pull-down menu. Complete the data table below by changing the mass as shown and recording the length of the year in seconds, and also measuring the distance from the planet to the sun at the closest point (perihelion) and farthest point (aphelion). (Make sure slider is set to most accurate) Mass of Sun (body 1) Mass of Planet (body 2) Closest Distance to Sun (perihelion) Farthest Distance to Sun (aphelion) Q: When is the planet moving fastest? Why? Q: What makes the length of the year increase and decrease? Why? Q: A planet in a circular orbit would always be the same distance from the sun. What do you notice about orbits with the shortest years? Why? Choose the ellipses preset from the pull-down menu. You may move the slider bar about 2/3 of the way towards fast for this simulation. Run the simulation until the green planet (body 4) returns to its starting point (one planetary year) In Orbit [ 8 ]

9 Planet Closest Distance to Sun (perihelion) Farthest Distance to Sun (aphelion) Purple Planet (body 2) Blue Planet (body 3) Green Planet (body 4) Change the y velocity of the blue planet (body 3) to 90 and the green planet (body 4) to 70. Run the simulation again until the green planet (body 4) returns to its starting point (one planetary year) Planet Closest Distance to Sun (perihelion) Farthest Distance to Sun (aphelion) Purple Planet (body 2) Blue Planet (body 3) Green Planet (body 4) estimate Q: How does the year of a planet closer to the sun compare with one that is farther away? Why? Q: How can an orbit be made more circular? Explain your answer. Q: In your own words describe what an orbit is and what factors affect the size, speed and time (period) of an orbit. In Orbit [ 9 ]