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INVESTIGATING STUDENT DIFFICULTIES WITH CONCEPTS OF GRAVITATION

INVESTIGATING STUDENT DIFFICULTIES WITH CONCEPTS OF GRAVITATION. Or. ...DO YOU UNDERSTAND THE GRAVITY OF THIS SITUATION?. Jack Dostal and David Meltzer Iowa State University. Why Gravitation? Lack of research on students’ concepts of gravity Similar in nature to Coulomb’s Law

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INVESTIGATING STUDENT DIFFICULTIES WITH CONCEPTS OF GRAVITATION

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  1. INVESTIGATING STUDENT DIFFICULTIES WITH CONCEPTS OF GRAVITATION Or...

  2. ...DO YOU UNDERSTAND THE GRAVITY OF THIS SITUATION? Jack Dostal and David Meltzer Iowa State University

  3. Why Gravitation? • Lack of research on students’ concepts of gravity • Similar in nature to Coulomb’s Law • Subject of interest in both physics and astronomy

  4. Previous Research • Not much! But here are a couple of examples: • Nussbaum, late 1970s - early 1980s (Israel) • Emphasis: Children’s concepts of the earth • What does Earth look like? Which way is down? • Instructional method: Audio-tape lessons • Gunstone and White, 1981(Australia) • Emphasis: First-year college students understanding of gravity • Students were presented a physical situation and asked to predict what would happen if a certain action was taken. • Students made observations and were asked to reconcile any discrepancies between their prediction and observation.

  5. Our Goals • To investigate students’ thoughts about gravitation • To develop instructional materials which enable students to learn about gravitation more effectively • To quantitatively evaluate the effectiveness of the materials produced

  6. Pretesting: What are the students thinking? • We have used two main diagnostic instruments: • Multiple choice questions: • 11-question pretest addressing many different aspects of gravitation (inverse square law, Newton’s 3rd Law, more) • Used at Southeastern Louisiana University, Iowa State University, and Hawkeye Community College • Free-Response questions: • 10 question pretest, all free-response and drawing • Used at Hawkeye Community College; will use at other schools in the near future

  7. Pretesting: What are the students thinking? Class profiles: SE Louisiana: Second-semester algebra-based physics students (N > 100)Multiple choice questions given on the first day of class Iowa State: Second-semester algebra-based physics students (N = 79)Multiple choice questions given on the first day of class Hawkeye CC: General education astronomy class (N = 21)Several weeks into course (Newton’s Laws and Universal Law of Gravitation mentioned, but not thoroughly covered)

  8. Selected results from multiple choice questions: Multiple choice Q1: The mass of the sun is about 3 x 105 times the mass of the earth. How does the magnitude of the gravitational force exerted by the sun on the earth compare with the magnitude of the gravitational force exerted by the earth on the sun? The force exerted by the sun on the earth is: A. About 9 x 1010 times larger B. About 3 x 105 times larger C. Exactly the same D. About 3 x 105 times smaller E. About 9 x 1010 times smaller

  9. Selected results from multiple choice questions: Multiple choice Q1: The mass of the sun is about 3 x 105 times of the mass of the earth. How does the magnitude of the gravitational force exerted by the sun on the earth compare with the magnitude of the gravitational force exerted by the earth on the sun? The force exerted by the sun on the earth is: A. About 9 x 1010 times larger B. About 3 x 105 times larger C. Exactly the same D. About 3 x 105 times smaller E. About 9 x 1010 times smaller

  10. Selected results from multiple choice questions: Multiple Choice Q1: SE Louisiana: less than 10% correct Iowa State: 14% correct Hawkeye CC: 19% correct Students in various settings/backgrounds/courses have the same misconception: Student thinking: Objects of unequal masses exert unequal forces on one another!

  11. E E E M M M E E E M M M Selected results from multiple choice questions: Multiple choice Q8: Which of the following diagrams most closely represents the gravitational forces that the earth and the moon exert on each other? (Note: The mass of the earth is about 80 times that of the moon) (A) (C) (E) (B) (D) (F)

  12. E E E M M M E E E M M M Selected results from multiple choice questions: Multiple choice Q8:Hawkeye CC results and Iowa State results: (A) 76%,38%(C) 14%, 6%(E) 10%,1% (B) 0%,44%(D) 0%,0%(F) 0%,0% Student thinking: Objects of unequal masses exert unequal forces on one another!

  13. Selected results from free-response questions: Earth asteroid Free Response Q2: Refer to the picture above. State whether the magnitude of the force exerted by the Earth on the asteroid is larger than, smaller than, or the same as the magnitude of the force exerted by the asteroid on the Earth. Explain the reasoning for your choice.

  14. Selected results from free-response questions: Earth asteroid Free Response Q2: Refer to the picture above. State whether the magnitude of the force exerted by the Earth on the asteroid is larger than, smaller than, or the same as the magnitude of the force exerted by the asteroid on the Earth. Explain the reasoning for your choice.

  15. Earth asteroid Selected results from free-response questions: Same as: 10% Smaller than: 5% Larger than:86% 76% of all students explicitly reasoned that because the Earth was larger or more massive, it exerted a greater force on the asteroid. LARGER objects exert MORE force on SMALLER objects... ...than SMALLER objects exert on LARGER objects.

  16. Selected results from free-response questions: • Free Response Q8: • Imagine that you are standing on the surface of the moon holding a pen in one hand. • A) If you let go of the pen, what happens to the pen? Why? • B) After you let go of the pen, what happens to you? Why?

  17. Free Response Q8: • Imagine that you are standing on the surface of the moon holding a pen in one hand. • A) If you let go of the pen, what happens to the pen? Why? 45% 31% 24% DROPS TO THE SURFACE FLOATS FLOATS AWAY

  18. Free Response Q8: • Imagine that you are standing on the surface of the moon holding a pen in one hand. • A) If you let go of the pen, what happens to the pen? Why? • DROPS TO THE SURFACE • Most cite the moon’s lesser gravity • “Like the astronauts” • FLOATS or FLOATS AWAY • Low gravity • Not enough gravity • No gravity • Weightlessness

  19. Free Response Q8: • Imagine that you are standing on the surface of the moon holding a pen in one hand. • B) If you let go of the pen, what happens to you? Why? 71% 5% 5% 19% YOU STAY ON THE SURFACE YOU FLOAT YOU FLOAT AWAY OTHER Students do not automatically consider gravitation to be universal!

  20. Selected results from free-response questions: Earth Free Response Q1: In the picture above, a person is standing on the Earth holding a ball in one hand. Draw the direction of the force exerted by the Earth on the ball in the picture above.

  21. Earth Free Response Q1: Correct (downward): Incorrect (upward): Incorrect (balanced): Do students really think that the ball will fall up? No. This appears to be a confusion of what is meant by a “force exerted by the Earth on the ball.” 67% 29% 5%

  22. M1 M2 Selected results from free-response questions: • Free Response Q7(A): • Two large masses M1 and M2 are in space as shown. • Where (if anywhere) can you place a third mass M3 to increase the total gravitational pull on M2? (This would increase the push or pull experienced by M2.) • Draw M3 in that position on the picture above and explain your reasoning for choosing that position.

  23. M1 M2 M3 M3 M3 M3 M3 M3 M3 Free Response Q7(A): Correct answers:67% Correct answers with correct reasoning (superposition of forces): 14%

  24. M1 M1 M2 M2 M3 M3 M3 M3 M3 • Free Response Q7(A): • Closeness: “M3 is closer to M2 than M1, so there is more force on M2” • “Tension” response: “M2 must now pull both M1 and M3, so there more force on M2”

  25. M1 M2 Selected results from free-response questions: • Free Response Q7(B): • Two large masses M1 and M2 are in space as shown. • Where (if anywhere) can you place a third mass M3 to decrease the total gravitational pull on M2? (This would decrease the push or pull experienced by M2.) • Draw M3 in that position on the picture above and explain your reasoning for choosing that position.

  26. M3 M3 M3 M3 M3 M3 M3 M3 M3 M1 M2 Selected results from free-response questions: Free Response Q7(B): Correct answers:38% Correct answers with correct reasoning (superposition/cancellation of forces): 29%

  27. M3 M3 M3 M1 M1 M2 M2 • Force Transmission : “M3 pulls on M1, so M1 pulls on M2 with less force.” • Free Response Q7(B) -- Reasoning for some incorrect answers: • Force Distribution I: “M1’s force is ‘used up’ on M3, so M1 pulls on M2 with less force.”

  28. M3 M1 M2 • Free Response Q7(B) -- Reasoning for some incorrect answers: • Force Distribution II: “M2 has to pull two objects, so the pull is less.” M1’s force on M2 depends in some way on M3!

  29. What’s next? • Create workbook-style instructional materials to teach gravitation • Field-test instructional materials in both physics and astronomy classroom settings • Evaluate the effectiveness of these materials • Further investigate student understanding through interviews and additional diagnostics

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