This was the fifth and final regular Investigation of the LabLearner CELL Our Solar System. In it, students explored the forces responsible for planetary motion and orbits.

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A. Begin the lesson by reviewing the movement of the planets.

1. Ask students: Around what large object do all planets move? All planets move around the Sun.

2. Ask students: Describe the movement of the Earth. The Earth rotates on its axis as it revolves around the Sun.

3. Ask students: What are the names of some other objects in the Solar System that revolve and rotate around the Sun? All of the known planets revolve and rotate around the Sun, including Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune.

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B. Remind students that in the lab, they investigated what affected the movement of the planets around the Sun. First, students used a moonball to help them think about movement.

1. Ask students: Using the moon ball, you explored two things that may affect movement. What were these two things? Students investigated forward motion and gravity.

2. Divide students into pairs. Ask students to work together to answer Problems 4a and 4b only. Students may refer to Problem 1a – h to help them recall their observations.

3. After students have answered Problems 4a and 4b, Ask students: Was the movement of the ball on the table the same as or different from the movement of the ball in the air? The movement was different. The ball on the table moved in a straight line across the table. The ball in the air moved in an arc or curved path until it hit the floor.

4. Ask students: If the movement of the ball was affected by gravity and forward motion each time, why was the movement different? Although gravity and forward motion affected the ball in both situations, the movement of the ball was different. This difference occurred because the table was able to hold up the ball, supporting it in spite of the force of gravity pulling on it.

5. Instruct students to answer Problem 4c in the Student Data Record.

6. Ask students to think about outer space. In outer space, there are very few objects. 

Ask students: Do you think that the movement of planets is more similar to the movement of the ball on the table (straight line) or in the air (arc)? Student answers may vary. The movement of the planets is more similar to the arc.

7. Begin talking about Trials 2 and 3 as you transition into the discussion of the orbit of the planets.

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C. Refer students to Trials 2 and 3, when students investigated the movement of the planets by using a ping pong ball in flour.

1. Instruct students to find Problem 5 in their Student Data Record. Instruct students to independently complete the problem by recording what each part of the model represented.

2. After students have finished, review their answers as a class. Ensure student understanding of the model before continuing with the analysis.

3. Remind students that throughout this CELL, they have been thinking about the movement of the objects in the Solar System.

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Cognitive Toolbox: Conclusions – Model the process of reviewing data and observations in order to come to a Conclusion. Tell students that good conclusions begin with a review of the Lab. As a class, review the following questions: 

a. Ask students: What was used to represent forward motion and gravity in the model? The turning of a student’s hand represented forward motion and the string represented gravity.

b. Instruct students to look at the diagram they drew in Problem 2e to find how these two things affected the movement of the model planet.

c. Ask students: How did the model planet move when affected by forward motion and gravity? The model planet moved in a ring or circular path.

d. Ask students to use their observations to make a conclusion about how real planets move. Instruct students to answer Problem 6 in the Student Data Record.

e. Remind students that holding the string represented gravity. 

Ask students: How was a planet without the Sun’s gravity modeled? Students let go of the string to find the path of a planet not influenced by the Sun’s gravity.

f. Instruct students to look at the diagram they drew in Problem 3e to find how the lack of the Sun’s gravity affected the movement of the model planet.

g. Ask students: How did the model planet move when not affected by the Sun’s gravity? The model planet moved out of its ring or circular path. The planet moved in a straight line from the path.

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D. As an extension of students’ experiments, ask students to think about the movement of the planets around the Sun in relation to the Moon’s movement around the Earth. The following questions may be helpful in promoting discussion.

1. Ask students: Is there any other object in the Solar System that orbits around an object? Yes, the Moon revolves around the Earth.

2. Instruct students to think about what they concluded about forward motion and gravity.

3. Ask students: What do you think affects the movement of the Moon around the Earth? Just as forward motion and gravity affect the movement of the planets around the Sun, forward motion and gravity affect the movement of the Moon around the Earth.

4. Ask students: When the planets orbit around the Sun, where does the pull of gravity come from? The pull of gravity comes from the Sun.

5. Ask students: When the Moon orbits around the Earth, does the pull of gravity that causes the orbit come from the Sun? If not, where does it come from? No. The pull of gravity that causes the orbit comes from the Earth.

Note: Gravitational force exists between the Sun and the Moon. However, the gravitational force between the Earth and the Moon is far greater; hence, the Moon orbits the Earth. 

6. If necessary, remind students that all objects have a force of gravity. The Sun’s gravity is very great because the Sun is a very large object. The Earth, although not as large as the Sun, is also sizable. For this reason, the Earth’s gravity is strong enough to pull the Moon toward it.

7. Ask students: What affects the orbit of the Moon around the Earth? Forward motion and the Earth’s gravity affect the orbit of the Moon around the Earth.

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E. Conclude by briefly reviewing the ideas addressed in this CELL. Use the completed Solar System Concept Map Transparency as a retrieval aid and support for students.

1. Instruct students to think about what they have learned about the Solar System.

2. Ask students: What are some important parts of or ideas about the Solar System and how does each affect us? Record student answers on the board. Student answers will vary. Some sample answers are included below: