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. OUTLINE: I. The Physics Education Research Group at ISU (ISUPERG) II. Why Gravitation? A. Some attention at grade school level B. Minimal treatment at HS-college level (aside from Newton’s laws) C. Middle ground between physics and astronomy D. Applicable to entry-level astronomy courses III. Pretesting: Student preconceptions/misconceptions A. The “MGDT” *What is it? *Examples (of questions) *Results B. The “DGDT” *What is it? *Examples (of questions) *Results OUTLINE (continued): IV. New Curriculum A. How can it be used? B. Potential partners *HCC -- Introductory Astronomy (gen. ed.) *UNI -- Astronomy (gen. ed.) *ISU -- Physics 111-112 V. Post-testing and results (which we don’t have) VI. Student Interviews (which we don’t have) VII. Ultimate goal of this research

4. ABSTRACT: Teaching the concept of gravity and the universal nature of gravitation in any physics or astronomy classroom can be difficult. Unlike subjects such as magnetism or optics for example, gravitation is difficult (or impossible, on astronomical scales) to demonstrate in a student laboratory. We have developed diagnostic instruments to identify students' initial concepts of gravitation, and have administered them in community-college and university settings. We are also developing materials to enable students to recognize incomplete and incompatible concepts, and to strengthen their understanding of the nature of gravitation. The target audience for these materials is the typical population of introductory astronomy and physics courses both science and non-science majors. We will report diagnostic data, as well as preliminary data from class testing of the curricular materials. Talk follows:

5. 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

6. 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.

7. 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

8. 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

9. 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)

10. Selected results from multiple choice questions : Multiple choice Q1: The mass of the sun is about 3 x 10 5 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 10 10 times larger B. About 3 x 10 5 times larger C. Exactly the same D. About 3 x 10 5 times smaller E. About 9 x 10 10 times smaller

11. Selected results from multiple choice questions : Multiple choice Q1: The mass of the sun is about 3 x 10 5 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 10 10 times larger B. About 3 x 10 5 times larger C. Exactly the same D. About 3 x 10 5 times smaller E. About 9 x 10 10 times smaller

12. Selected results from multiple choice questions : Multiple choice #1 Student concepts: The GREATER the mass of an object, the GREATER its force on another object. Which is great! But… When one object is LARGER than another, it exerts MORE force on the smaller object than the smaller object exerts on the larger object.

13. 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!

14. 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) E M E M E M E M E M E M (A)(C)(E) (B)(D)(F)

15. Selected results from multiple choice questions : Multiple choice Q8:Hawkeye CC results and Iowa State results: E M E M E M E M E M E M (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!

16. Earth asteroid Selected results from free-response questions : 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.

17. Earth asteroid Selected results from free-response questions : 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.

18. 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.

19. 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? Selected results from free-response questions :

20. 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 FLOATS FLOATS AWAY 45% 31% 24%

21. 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

22. 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? YOU STAY ON THE SURFACE YOU FLOAT YOU FLOAT AWAY 71% 5% 19% OTHER Students do not automatically consider gravitation to be universal!

23. 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. Earth Selected results from free-response questions :

24. Earth Free Response Q1: Correct (downward): Incorrect (upward): Incorrect (balanced): 67% 29% 5% 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.”

25. Free Response Q7(A): Two large masses M 1 and M 2 are in space as shown. Where (if anywhere) can you place a third mass M 3 to increase the total gravitational pull on M 2 ? (This would increase the push or pull experienced by M 2.) Draw M 3 in that position on the picture above and explain your reasoning for choosing that position. M1M1 M2M2 Selected results from free-response questions :

26. M1M1 M2M2 Free Response Q7(A): Correct answers:67% Correct answers with correct reasoning (superposition of forces):14% M3M3 M3M3 M3M3 M3M3 M3M3 M3M3 M3M3

27. “Tension” response: “M 2 must now pull both M 1 and M 3, so there more force on M 2 ” M1M1 M2M2 M3M3 Free Response Q7(A): Closeness: “M 3 is closer to M 2 than M 1, so there is more force on M 2 ” M1M1 M2M2 M3M3 M3M3 M3M3 M3M3

28. Free Response Q7(B): Two large masses M 1 and M 2 are in space as shown. Where (if anywhere) can you place a third mass M 3 to decrease the total gravitational pull on M 2 ? (This would decrease the push or pull experienced by M 2.) Draw M 3 in that position on the picture above and explain your reasoning for choosing that position. M1M1 M2M2 Selected results from free-response questions :

29. M1M1 M2M2 Free Response Q7(B): Correct answers:38% Correct answers with correct reasoning (superposition/cancellation of forces):29% M3M3 M3M3 M3M3 M3M3 M3M3 M3M3 M3M3 M3M3 M3M3

30. Free Response Q7(B) -- Reasoning for some incorrect answers: Force Distribution I: “M 1 ’s force is ‘used up’ on M 3, so M 1 pulls on M 2 with less force.” M1M1 M2M2 M3M3 M3M3 Force Transmission : “M 3 pulls on M 1, so M 1 pulls on M 2 with less force.” M1M1 M2M2 M3M3

31. Free Response Q7(B) -- Reasoning for some incorrect answers: Force Distribution II: “M 2 has to pull two objects, so the pull is less.” M1M1 M2M2 M3M3 M 1 ’s force on M 2 depends in some way on M 3 !

32. 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