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Students Alternative Conceptions in Understanding of Sound

Zdeslav Hrepic Kansas State University Physics Education Research Group. Students Alternative Conceptions in Understanding of Sound. The Aim of Research and Methods. The aim - to find or confirm: students’ alternative conceptions related to the sound, their origins and representation

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Students Alternative Conceptions in Understanding of Sound

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  1. Zdeslav Hrepic Kansas State University Physics Education Research Group Students Alternative Conceptions in Understanding of Sound

  2. The Aim of Research and Methods • The aim- to find or confirm: students’ alternative conceptions related to the sound, their origins and representation • Through written, open-ended, conceptual questions (in Croatian) • During 1997, immediately after lectures on sound • 287 examinees (divided in 4 groups - percentages) • 3 levels - 8th grade elementary (El), high school (HS) and college level (Col) • All inSplit, Croatia

  3. Sound Propagates As aParticle-Like Object (1of 2) The particles of the sound • “[In water] we hear sound [from air] weakly and unrecognizably becausethe particles of the soundcan not penetrate the water. It has dense molecular structure“ (El) Sound breaks its way through materials: • "Sound propagates in the way that it acts with force on particles of materialwhich it passes through. Denser the material – sound propagates weaker..“(El)

  4. Sound Propagates As a Particle-Like Object (2 of 2) The sound occupies certain volume: • “Sound passes slower [in denser materials] because it is dense and there is no space for it“ (El) Aerodynamics of sound: • “..sound of violin …is thinner and faster in the air [than sound of contrabass] “ (El) • “Travels faster. Because violin sound is sharper” (El)

  5. Material Obstacles Slow Down Propagation of Sound (60% - 19%) • “…the sound propagates slower if it comes across the barriers.“ (El) • “…wooden barrierslows downspeed of sound.“(Col)

  6. If Louder, Sound Travels Faster (36% - 60%) • “Sound of stronger loudspeaker travels fasterbecause it is stronger.“ (HS) • “Sound of stronger loudspeaker travels faster than sound of the weaker one. It travels faster because it has stronger power and sound automatically spreads faster.“ (El)

  7. Speed of Sound Depends on Movement of Sound Source (62% - 23%) • “Sound of siren travels faster[toward the observer]when automobile moves toward the observer“ (Col) 43% Stated reasons why: • Frequency is higher • Distance gets shorter • Speed of automobile carries that sound • “Speed of sound towards listener is increased for the amount of the speed of automobile.“ (HS)

  8. Sound Energy Is Not Generally Transformable (68% - 13%) Sound can not be transformed in some way into light because: • “…they are two completely different phenomenon” (El) • “…sound is mechanical wave, and light is electromagnetic.“(Col) • “…the sound is something perceived with ear and the light is perceived visually.” (HS) • “…the sound can not reach speed the of light.” (HS) • “such a transformation of energy is not possible“ (HS) • “light is transversal, and sound is longitudinal wave.“ (HS)

  9. Denser the Medium, Sound Propagates Faster (45% - 36%) (1of 2) • ”For sound (mechanical wave) the medium is necessary. If it is necessary that means that if the material is denser the speed of the sound is greater.” (HS) • ”When the density is greater the sound is faster because the particles are nearer so the activity among them is conveyed faster.” (Col) • “When the material is denser then the sound spreads faster. An example: “The sound is faster in water than in air” (HS)

  10. Denser the Medium, Sound Propagates Faster (45% - 36%) (2 of 2) • "If particles[of medium]are denser, soundwill move slower because itmust break through this density.“ (El) • "Less the density, greater propagating velocity...it is logical thatif wave collides with particles, propagating velocity will be smaller.“ (Col) • "Honey does not conduct sound, because itsdensity is big enough to prevent propagation of sound. (Col)

  11. Not All the Materials Can Conduct the Sound(44% - 45%) HONEY • 44% DOES NOT • 15% conducts poorly • 30% DOES conduct PLASTICS • 31%DOES NOT • 9%conducts poorly • 45%DOES conduct Why NOT? • Too Dense – 30% • Insulator – 1% • No explanation – 13% Why NOT? • Its Structure – 5% • Too Dense – 3% • Too Stiff – 3% • Insulator – 3% • No explanation – 18%

  12. Speed of Sound Depends on Its Frequency (47% - 37%) • “…speed depends on frequency; so the higher is the frequency, the greater is the speed.” (Col) 37% • ”v=/T=f . The sound of the violin travels faster.” (HS) • ”The sound of the violintravels faster because it is thinner; it produces more vibrations per second. I would describe it as the lighter sound, because thesound of the contrabass is deep, it spreads across the air very hardly.” (El)

  13. Wind Influences the Frequency of Received Sound (33% - 10%) f=? • ”Yes, it will. The frequency will be higher if the speed of the sound is greater and vice versa.” (HS) 23% • ”…v =λ/T, f = 1/T v= λf → v~f“ (Col) • ”…We will have a feeling that the source was displaced and according to Doppler’s effect it influences the frequency.” (Col) Wind direction a) b)

  14. Conclusion – Percentages and Categorization of Students Difficulties 50% - affirm alt. conceptions: 59% - 47% - 48% 32% - negate alt. conceptions: 21% - 36% - 42% 1. Students’ models of propagation of the sound and their consequences: particle – particle pulses – wave 2. Relation of the sound to the other physical phenomena (waves, light, energy, electricity, pressure, force…) 3. Misinterpretations of graphics, formulas, definitions and terms learned in school http://www.phys.ksu.edu/~zhrepic/

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