Identifying Students' Mental Models of Sound Propagation Zdeslav Hrepic Masters thesis Kansas State University Physics Education Research Group Supported by NSF ROLE Grant # REC-0087788

Motivation Construction of Model Analysis Inventory Model Analysis Analytical method for analyzing students’ mental models. Developed by Bao (1999). Model analysis inventory A tool for implementation of model analysis A set of multiple choice questions used with class response system and analytical software Enables quantitative display of students’ mental models in a real time (e.g. during the lecture) Must be specifically constructed for different science topics

Why sound? Everyday phenomena, constantly observed Research indicates that sound is an area in understanding of which students display numerous difficulties. Importance of waves in both, classical and modern physics.

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?

Methodology Research and analytical framework Phenomenographic research method Research tool Semi-structured interview protocol 9 contexts

Interview Protocol Context 1 – Voice-Ear How does sound propagate in this situation?   SPEAKER LISTENER

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

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

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

Context 5, 5a – Voice-String and Cans-Ear Experiment 1 Experiment 2 SPEAKER LISTENER SPEAKER LISTENER Compare and explain: Propagation of human voice through the: (5) tight string and cans vs. the air alone (5a) tight string and cans vs. the loose string and cans  

P-World students: KSU concept-based introductory physics class Participants P-World students: KSU concept-based introductory physics class Main sample: 16 students interviewed before and after instruction 8 students with 2 semesters of high school physics 8 students with no high school physics Additional sample: 8 students interviewed only once 6 students interviewed only after instruction 2 students interviewed only before instruction

Intro to Findings: Language degeneracy as Data Analysis Problem While describing sound propagation, students frequently use the same terminology that experts do, but often with different meaning or without any meaning.

Data Analysis Problem: Language degeneracy – Example Expert: “In this chapter we shall focus on sound waves that travel through the air and that are audible to the people (Halliday, Resnick, & Walker, 1997, p. 426). Expert: “Most sounds that we hear are transmitted through the air” (Hewitt, 1998, p.344) Student (no high school physics. Pre-instruction interview) I: Does air play any role in this process of propagation of sound? JEWEL: I think air plays for the fact that the sound travels through the air and it isn’t really doing anything else…it’s just wave transmission to the listener’s ear. Later: Paraphrased statement: In a vacuum sound “echoes” better than in air as there is nothing to absorb it there

Language degeneracy - Example Expert: “This vibrating material then sends a disturbance through the surrounding medium, usually air…” (Hewitt, 1998, p.342,3) Student: (two semesters of high school physics. Post-instruction interview) I: How does the sound propagate in this situation? JORDAN: So the speaker creates, kind of like disturbance…and…eventually…it’ll come over to the person’s ear and the ear will pick up disturbance and it’ll be able to translate it to the sound. … I: In space without air would anything be different for sound? JORDAN: (Pause) Probably it’ll, it wouldn’t a…it wouldn’t slow down, it’d just keep traveling.

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)

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.

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.)

Sound Properties Uniquely Associated with Entity Model Material - Sound is a material unit that propagates (of substance, has mass). INTERVIEWER: Does sound consist of anything material? (This question was posed after a student stated that sound is independent.) VIRGINIA: Yes, I don’t know of what, but yes, I am sure it does. Propagation of sound particles - Sound is the propagation of sound particles that are different from particles of the medium. STAR: “Well, the air is what…the sound particles move through.”

Independent Sound is independent – sound propagates through the vacuum (does not need medium). Example: INTERVIEWER: Would anything be different for sound in space with and without air? ASHLEY: …I guess if there’s no air then there is nothing for them [sound waves], nothing to get in the way, so they travel, like free of interference.

Material Sound is material material unit, of substance, and/or has mass. Example: INTERVIEWER: Does sound consist of anything material? (This question was posed after a student stated that sound is independent.) VIRGINIA: Yes, I don’t know of what, but yes, I am sure it does.

Seeping Sound passes (seeps) through empty spaces between the medium particles. Example: LORAIN: “…As the sound comes through [the air] I think…it might find the spaces in between the particles [of the air] but, I think eventually it might also hit one. I mean it’s not like it knows exactly where it’s going.”

Propagation of sound particles Sound is propagation of sound particles that are different from medium particles. Example: STAR: “Well, the air is what…the sound particles move through.”

Hybrid Models Composed of entity model (initial) and wave (target) model components At the same time distinct from each of the constituent models: by one or more features pre-defined as incompatible with respective parent model.

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

Hybrid Models Expressed by Single Student Vibrating air model Sound propagates through the air, which constantly vibrates horizontally back and forth. When the source produces sound it uses this motion of medium particles to travel toward the listener. Vibration of the air particles is identical with and without sound

Hybrid Models Expressed by Single Student 2. Ether model - Sound is a propagation of the disturbance of an ether-like medium composed of particles that are different from those of any physical medium. 3. Ether and Compression model - Incorporates compressions and rarefactions of actual physical medium into ether model reasoning Greater predictive power Students called these etheric particles - sound, sound waves and sound particles.

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

Pre instruction interview Post instruction interview Pre-Post instruction Model dynamics Students With No H.S. physics Pre instruction interview Post instruction interview Entity Model Entity Model Entity and Hybrid Entity and Hybrid Hybrid Models Hybrid Models Hybrid and Wave Hybrid and Wave Wave Model Wave Model

Pre instruction interview Post instruction interview Pre-Post instruction Model dynamics Students With 2 Semesters of H.S. Physics Pre instruction interview Post instruction interview Entity Model Entity Model Entity and Hybrid Entity and Hybrid Hybrid Models Hybrid Models Hybrid and Wave Hybrid and Wave Wave Model Wave Model

Pre instruction interview Post instruction interview Pre-Post instruction Stretched Model dynamics Students With No H.S. Physics Pre instruction interview Post instruction interview Entity Model Entity Model Entity and/or Hybrid Entity and/or Hybrid Hybrid Model Hybrid Model Hybrid and/or Wave Hybrid and/or Wave Wave Model Wave Model

Model States x x x x x x Context 1 x x x x x x x x x Context 2 x x x x Knowledge elements related to Model 1 only Knowledge elements related to Model 2 only x Knowledge elements related to both models or neither one No Model State Pure Model 1 State Pure Model 2 State Mixed Model State Hybrid Model State x x x x x Context 1 x x x x x x x x x Context 2 x x x x x x x x x

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. Since contexts were presented one after another and were all dealing with the same topic students perceived them more mutually co-related. Data analysis approach reduced the number of observed mixed model states.

Identified Mental Models Conclusions Identified Mental Models Eight mental models of sound propagation were identified. 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.

Are These Mental Models or Something Else? “Weak” definition Mental model is an internal representation, which acts out as a structural analogue of situations or processes and that serves to explain and predict the physical world behavior (Greca & Moreira, 2002) “Strong” definition Mental model has: spatial configuration of identifiable kinds of things (a few) principles of how system works and (certain) predictive power (diSessa, 2002) All models except one (ether model), satisfied the strong definition in at least two contexts

Thank You 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 inventory on sound propagation. Thank You