Relative Motion Demo Less Son Plan

Debra Lee

October 24, 2005 Relative Motion of the Moon, Earth and Sun Demonstration Lesson Plan

Grade Level Grade 10 Earth Science Class Lesson Overview This lesson will introduce students to the idea that all motion is relative to other motion by observing the movement of the Sun, Moon, and Earth. They will learn more about why these solar system bodies move as they do and how our understanding of their motion changes when we change the reference frame we are in. Most students have seen typical textbook pictures of a motionless Sun with a circle around it to represent the orbit of the Earth and similar pictures of the Moon revolving around the Earth. They do not realize that the Sun has rotational and translational motion and that the Sun’s gravitational pull affects the Moon’s orbit as well as the Earth’s. They also do not realize that the Moon’s mass causes a gravitational pull on the Earth in addition to the pull on the Moon by the Earth. The motions, therefore, of objects in our solar system are much more complicated than typical diagrams imply and students believe. This fact will be demonstrated using fruit (to represent the Earth, Sun, and Moon) moved in appropriate ways. This lesson is part of a unit that teaches about the solar system. The overarching idea of this unit is the eternal quest of scientists to answer the questions “How did our universe begin?” and “What is the structure of the universe?” At this point, the students have already reviewed the facts about the planets, moons, and Sun. They have learned the history of discoveries about the solar system, including the Ptolemaic and Copernican models. They have discussed orbits and gravitation. After this unit, the students will review how the relative motions of the Earth, Moon, and Sun result in the phases of the moon and eclipses. The following units will address the Stars and Galaxies and the Evolution of the Universe. Learning Outcomes • Learning Performances o Students will be able to describe the orbital motions of the Earth and Moon about the Sun, in addition to being able to describe the rotational and translational motions of the Sun. o Students will be able to explain that the typical textbook pictures of the solar system can be drawn differently if their motions are viewed from a different frame of reference. • Links to Standards o Benchmarks for Science Literacy Grades 9-12: 4G.1. Forces of Nature. Gravitational force is an attraction between masses. The strength of the force is proportional to the masses and weakens rapidly with increasing distance between them. o Benchmarks for Science Literacy Grades 9-12: 4F.2. Motion. All motion is relative to whatever frame of reference is chosen, for there is no motionless frame from which to judge all motion. EDUC 422

1

Debra Lee

October 24, 2005 o Benchmarks for Science Literacy Grades 6-8: 4A.3. The Universe. Nine planets of very different size, composition, and surface features move around the Sun in nearly circular orbits. The Earth is orbited by one Moon, many artificial satellites, and debris.

Students’ Prior Knowledge This lesson will broaden students’ understanding about the motions of the Sun, Earth, and Moon. The misconceptions that will be addressed include: 1) the Sun does not move, 2) the Moon does not revolve about the Sun, 3) the Moon’s mass does not cause a gravitational pull on the Earth. Prior knowledge important to the understanding of this lesson includes: 1) orbits are the paths that objects take around other objects as a result of gravitation and orbital velocity, 2) the Earth takes 365 days to revolve around the Sun and the Moon takes 29.5 days to revolve around the Earth, 3) every object exerts gravitational force on every other object, 4) knowledge of the relationship of the planets and their moons to the Sun. Establishing Purpose Ideas are sometimes not as simple as they seem. Additionally, the perspective from which something is viewed can change how it looks, even in science, where students assume all things are absolute. Historically, many astronomers have had misconceptions because their perspective was limited. This lesson will be presented as a way to “blow a hole” in what the student knows, and “fill the hole” with new, more complete knowledge. Students are reminded that even today many scientists in the field of astronomy are getting “holes blown in their knowledge” as new discoveries are made. Scientists have to keep an open mind and look at problems from many perspectives as they look for answers to such perplexing questions as “How big is the universe? Is the universe expanding or contracting? How did the universe begin?” Instructional Strategies The following instructional strategies will be used: 1) questioning, 2) modeling, 3) demonstration, 4) computer animation, 5) class discussion, 6) written assessment, and 7) internet research. Materials Needed o A grapefruit to represent the Sun, a lime to represent the Earth, and a grape to represent the Moon. o Computer and screen to display the following website: http://www.pbs.org/wgbh/nova/tothemoon/puz2n3.html o Post-lesson assessment. o Chalk/whiteboard or overhead. o Video disc of relative motion. Time required One fifty minute class period.

EDUC 422

2

Debra Lee

October 24, 2005

Instructional Sequence Introduction o Write on the board: “Relative Motion” and “Motion of the Earth, Moon, and Sun”. o Begin by telling the class that you are going to “blow a hole in what they know” and fill it with new knowledge. Explain “there are some things in science you probably think you know, but you don’t know everything.” Ask, with a show of hands, “Who knows how the Sun, Earth and Moon move?” o Ask a volunteer to draw on the board the motions of the Sun, Earth, and Moon. o They will probably draw a diagram that looks similar to this:

Remind the students that these “paths” are called orbits, they are a result of gravitational pull and orbital velocity, and all of the orbits are counterclockwise. o Explain that this diagram is one way to think about the motion of the Sun, Earth, and Moon, and it is not wrong, but this diagram does not tell the entire story. Relative Motion o Discuss relative motion. How do we know that something is moving? Show video disc of two trains and a man walking on a boat close to shore. Write on the board “All motion is relative to whatever frame of reference is chosen, because there is no motionless frame.” Discuss, asking the following questions: 1) What is a frame of reference? 2) Why is there no motionless frame? 3) What frame of reference do we usually use when we are describing motion? Motions of the Sun and Earth o Tell the students that first of all we will talk about the motions of the Sun and the Earth. Ask the students, “Does the Sun move? How do we know?” Explain that the Sun rotates every 27 days at its equator and moves through the universe at 19.7 km/sec (44,000 mph) as it revolves about the Milky Way galaxy. It is tilted at a 25 degree angle and headed toward the Hercules constellation. This is the Sun’s motion relative to the other stars in our galaxy. Model the Earth’s and Sun’s motions using the grapefruit and lime. Ask the students, “Do you still think the Earth moves in a circle around the Sun?” Confirm that the Earth moves in a spiral around the Sun relative to the other stars. Motions of the Earth and Moon

EDUC 422

3

Debra Lee

October 24, 2005

o Ask students, “Does the Moon revolve around the Earth?” Does the Earth revolve around the moon?” Explain that the Earth and Moon revolve around each other because of the relatively large size of the Moon’s mass. They revolve around a point called the barycenter, which is their center of mass. The barycenter of the Earth/Moon system is slightly below the surface of the Earth. Compare this motion to two dancers who are holding hands and spinning. The larger person has more influence on where the smaller partner goes. Model using the lime and grape. Explain that the barycenter revolves about the Sun and the Earth and Moon revolve about the barycenter. This means that the Earth and Moon each have orbits around the Sun, but they are intertwined with each other. The Earth’s and Moon’s orbits are said to have a wobble. o Scientists have discovered moons on distant planets like Pluto, by first observing the planet’s “wobbled” orbit. o Show animation on the computer and explain how this motion appears to us on Earth as the Moon rotating about Earth. http://www.pbs.org/wgbh/nova/tothemoon/puz2n3.html Conclusion o Conclude the lesson, by asking students to explain the relative motion of the Earth, Moon, and Sun. Clarify and summarize. Discuss how a student correcting their preconceptions is similar to ancient astronomers figuring out their misunderstandings about the solar system. o Complete worksheet (See Assessing Student Understanding below). o Ask the student to do research on the internet to find support for these ideas. Assessing Student Understanding Students will be asked to work in pairs as they fill out the attached worksheet that requires the students to: 1) describe the motion of the Sun and the Earth 2) describe the motion of the Moon and Earth relative to the Sun, including reasons for the motion that occurs, 3) list 3 questions they still have about what they learned today. (Have extra fruit available if any students want to try to model the motion themselves.) Rationale The introduction of this lesson is intended to pique the students’ interest by challenging their prior knowledge about the motion of the Sun, Earth, and Moon. Wright (1995) explains that discrepant events, such as the fact that the moon and sun revolve around each other, are powerful devices “to stimulate interest and motivate the use of thinking skills in learning science concepts and principles at a deeper level.” As suggested by Donovan and Bransford (2005), resilient preconceptions must be engaged in the learning process and science is about questioning the obvious. The demonstration using fruit is a model to provide the students with a visual representation of the Earth/Moon/Sun relationship, so they can correct their preconceptions. The computer animation shows a relatively complicated relationship between the Earth and Moon is a simpler way, in another opportunity to correct preconceptions. The questioning and discussion format allows presentation of the key concepts, with opportunities for formative assessment at the same time the students’ understanding deepens by explaining their ideas to the class. The pace of the class can be adjusted by the level of understanding that is demonstrated EDUC 422

4

Debra Lee

October 24, 2005

by the students during the questioning. Assessment is also achieved by asking the students to write/diagram their explanations, and deeper thinking about these concepts is achieved through asking the students to come up with 3 more questions related to this lesson. Finally, research on the internet to find support for the concepts learned in this lesson will verify the importance and accuracy of the ideas and promote the continued inquiry into the ideas of relative motion, the motion of the Earth, Sun, and Moon, and their relationship to other bodies in the universe.

Sources The idea for this demonstration lesson plan was from Ms. Kathy Kibbie, field instructor. American Association for the Advancement of Science. (1993). Benchmarks for science literacy. New York: Oxford University Press. Donovan, M. S. & Bransford, J.D. (Eds.), (2005). How students learn: Science in the classroom. Washington, DC: National Academy Press. Love, D. J. (n.d.). The moon's motion. Retrieved Oct. 22, 2005, from Principles of Astronomy Web site: http://www.synapses.co.uk/astro/moon1.html. Wright, E. (1995). Discrepant event demonstrations. The Science Teacher, 62(1), 24. To the moon. (n.d.). Retrieved Oct. 22, 2005, from Luna Puzzlers Web site: http://www.pbs.org/wgbh/nova/tothemoon/puz2n3.html. Video disc of relative motion

EDUC 422

5

Debra Lee

Name______________________________________

October 24, 2005

Date____________________

Answer the following questions as completely as possible. You may add diagrams as needed to clarify your answers. 1. What does relative motion mean? Give an example. Relative motion is motion that depends on what frame of reference you are in. For example, from the Earth it looks like the Moon is revolving around the Earth. From the Sun, it looks like the Earth and Moon are both revolving around the Sun. 2. Pretend you are sitting on a distant star within the constellation Hercules looking through a powerful telescope that allows you to see the Sun and Earth. Describe the motion of the Sun and the Earth. The Sun, while tilted at a 25 degree angle, is moving through the Universe toward the constellation Hercules. The Earth is orbiting around the Sun, so it is moving in a spiral through space. Now you are sitting on the Sun. Describe the motion of the Earth. The Earth is revolving about the Sun in an elliptical orbit. 3. Pretend you are still sitting on the Sun. Describe the motion of the Moon. Why does it move this way? The Earth and Moon are both revolving around the Sun, with their orbits weaving in and out of each other. The Earth and Moon rotate about their barycenter, which is slightly below the surface of the earth. The gravitational pull of the Sun on the Earth/Moon system determines their orbits. 4. Name an astronomer who had a misconception about something in the Universe. Describe the misconception and how it was proven wrong. Ptolemy believed that the Sun revolved around the Earth. Improved observations made by Brahe along with Kepler’s Laws proved the Copernican model was correct.

EDUC 422

6

Debra Lee

October 24, 2005

5. List 3 questions that you would like to ask related to what we learned today.

EDUC 422

7