Zdeslav Hrepic Dean A. Zollman N. Sanjay Rebello

1. Zdeslav HrepicDean A. ZollmanN. Sanjay Rebello Students' Mental Models of Sound Propagation 125th AAPT National MeetingBoise, Idaho Kansas State UniversityPhysics Education Research Group Supported by NSF ROLE Grant # REC-0087788

2. Research Questions • What mental models of sound propagation do students use? • How do students’ mental models change with context? • How do students’ mental models change after the instruction?

3. Methodology Research tool • Semi-structured interviewprotocol • 9 contexts Participants • KSU concept-based introductory physics class • Main sample: 16 studentsinterviewed before and after instruction • 8 students with 2 semesters of high school physics • 8 students with no high school physics

4. A Glimpse Into Interview ProtocolContext 1 – Voice-Ear How does sound propagate in this situation?   SPEAKER LISTENER

5. Context 2 – Voice-Dust Particle Is there any effect of sound propagation on the dust particle?   SPEAKER DUST PARTICLE LISTENER

6. Context 3, 3a – Loudspeaker-Dust Particle Is there any effect of sound propagation on the dust particle? LOUDSPEAKER DUST PARTICLE LISTENER (3) Constant tone(3a) Beating tone

7. Contexts 4,4a – Voice-Obstacle-Ear Two people are in different rooms separated by a brick wall. Can they hear each other if the speaker is loud? If so,how does the sound get to the other side of the wall? SPEAKER LISTENER Macroscopic level Microscopic level

8. Model Identification and Model Context Dependence Determining the model • By the definitions constructed from students’ descriptions. • By sound properties recognized as uniquely associated with the respective models. Probing for model context dependence • Models were identified within single contexts (no generalizing of statements across the contexts)

9. Findings – Identified Models • Wave model - Scientifically accepted model • Entity model - Dominant alternative model: Sound is a self-standing, independent entity different from the medium through which it propagates. • Hybrid models - Composed of entity and wave model features and at the same time they are incompatible with both, the entity and wave models.

10. Sound Properties Uniquely Associated with Entity Model • Independent - Sound propagates through the vacuum (does not need a medium). • Material - Sound is a material unit that propagates (of substance, has mass). • Seeping - Sound passes (seeps) through empty spaces between the particles of the medium. • Propagation of sound particles - Sound is the propagation of sound particles that are different from particles of the medium.

11. Wave Model - In Student’s Words… I: So what is sound wave? MR.T: Sound wave is um…nothing more than a motion, disturbance in the air, moving in one direction. I: OK. So what is disturbed? MR.T: The position of the particles. They don’t move up and down, just this way back and forth. I: OK. So does air play a role in this propagation MR.T: Yes. I: So what’s the role of the air? MR.T: The particles of the air, little molecules that make up the air make the…Through the motion they create the wave. (Student with two semesters of high school physics. Post-instruction interview.)

12. Hybrid Models Expressed by More Than One Student 1. Shaking model – Sound is a self-standing entity different from the medium, but as it propagates through the medium it causes vibration of the particles of/in the medium. 2. Longitudinally shaking model – A special case of the shaking model: Propagation of the sound-entity causes longitudinal vibration of the particles of/in the medium. 3. Propagating air model – Sound propagates so that air particles travel from the source to the listener. +Three other hybrid models each expressed by single student

13. Model States Features related to both models or neither one Features related to Model 1 only Features related to Model 2 only x NoModelState Pure Model 1 State Pure Model 2 State Mixed Model State Hybrid Model State x x x x Context1 x x x x x x x x x x x x Context2 x x x x x x x

14. Mental Models - Context Dependence Multiple models were found in only 2 of 32 interviews Possible explanations: • Mental models are weakly context sensitive in this domain. • Data analysis approach reduced the number of observed mixed model states. • Model identification required all necessary model features within a single context. • Several different effects of sound propagation on the particles of/in the medium were consistent with the entity model.

15. Pre-Post Instruction Model Dynamics Pre instruction interview Post instruction interview Entity Model Entity Model Entity and Hybrid Entity and Hybrid Hybrid Model Hybrid Model Hybrid and Wave Hybrid and Wave Wave Model Wave Model

16. Conclusion Identified Mental Models • Eight mental models of sound propagation wereidentified. • There are only two fundamental models of sound propagation: • Wave model - the scientifically accepted model • Entity model - dominant alternative model • All other models appear as a result of fusing two fundamental models into hybrid models.

17. Future Research • Investigating mental models of sound propagation in algebra- and calculus-based introductory physics courses. • Further investigating the fine structure of mental models and its role in model dynamics. • Creating a model analysis inventory on sound propagation.

18. More Information zhrepic@phys.ksu.edu http://www.phys.ksu.edu/~zhrepic/