Zdeslav Hrepic Dean A. Zollman N. Sanjay Rebello

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Students' Mental Models of Sound Propagation

• Zdeslav HrepicDean A. ZollmanN. Sanjay Rebello

125th AAPT National MeetingBoise, Idaho
Kansas State UniversityPhysics Education
Research Group
Supported by NSF ROLE Grant REC-0087788
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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?

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Methodology

• Research tool
• Semi-structured interview protocol
• 9 contexts
• Participants
• 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

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A Glimpse Into Interview ProtocolContext 1
Voice-Ear
How does sound propagate in this situation?
  SPEAKER LISTENER
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Context 2 Voice-Dust Particle
Is there any effect of sound propagation on the
dust particle?
  SPEAKER DUST PARTICLE LISTENER
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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
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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
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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)

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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.

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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.

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Wave Model - In Students Words

• I So what is sound wave?
• MR.T Sound wave is umnothing 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 dont
  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 whats the role of the air?
• MR.T The particles of the air, little molecules
  that make up the air make theThrough the motion
  they create the wave.
• (Student with two semesters of high school
  physics. Post-instruction interview.)

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

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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
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Conclusion
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.

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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.

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More Information
zhrepic_at_phys.ksu.edu http//www.phys.ksu.edu/zhre
pic/