Students, Teachers, And Textbook Conception Of The Physics Of Sound

CONCEPTIONS OF SOUND: West Kalimantan Case

Leo Sutrisno Dept. Math and Science Education

Faculty of Education Tanjungpura University Pontianak, Indonesia 1. Textbooks’ presentation of the physics of sound 1.1 The generation of sound 1.2 The transmission of sound 1.2 The detection of sound 2

Teachers' knowledge of the physics of sound

2.1

The generation of sound

2.2

The transmission of sound

2.3

The detection of sound

3. Students' pre-conceptions about sound 3.1 The generation of sound 3.2 The transmission of sounds 3.3 The medium of the transmission of sound 3.4 The velocity of sound 3.5 Light velocity vs sound velocity 3.6 The night phenomena of sound transmission 19

3.7 The sound of thunder 3.8 The loudness of sound 3.9 The Doppler Effect 3.10 The effect of the gravitational force on sound

List of figures Figure 3.1 A model of the transmission of sound

List of Tables Table 3.1 Percentages of students who held different ideas from scientists' ideas related to sound phenomena Table

3.2

Distribution

of

χ2

values

of

each

sound

phenomenon by students' achievement, gender, and ethnic group

20

This presentation discusses concepts of sound. The concept as presented in Indonesian senior high school textbooks will be the first. Although it is hoped that teachers' conceptions would be consonant with scientists' conceptions, it would be valuable to examine this assumption. As a focus for the discussion, students' ideas about sound before they have been taught (students' pre-conceptions) at secondary level will be presented in detail.

1. Textbooks' presentation of the physics of sound Up to the middle of 1990s, textbooks are of great concern in West Kalimantan. They are relatively expensive and not readily available in some places. Most book stores are located in the cities and distributed by the Ministry of Education and Culture. These books are collectively called buku paket. Originally these books were intended to accompany the dissemination of the new curriculum in 1975 and there was no revision. It was compulsory for schools to use these books even if they were unable to provide a book for each student. In such schools teachers carried the books from one class to another, so most students were only able to read buku paket during class time. At secondary school level, the buku paket of physics is Energi, gelombang aan meaan (EGM) [Energy, wave and field]. Some contributing authors were university and college lecturers and others were school teachers. There are two other physics textbooks which are available in several book stores: Buku Pelajaran Fisika vntuk sMA (the General Senior High School physics textbook] written by Widagdo Mangunwiyoto, and Penuntun Pelajaran Fisika berdasarkan kurikulum 1984 untuk SMA [the General Senior High School physics guide book based on the Curriculum - 1984], written by Kamajaya and Suardhana Linggih.

1.1

The generation of sound

No one textbook gives an entirely clear definition of sound. Mangunwiyoto writes "sound is a kind of 21

disturbance which can be detected by ears" (p.34) - bunyi adalah jenis usikan yang dapat diditeksi oleh telinga. The word usikan has been used in the previous chapter to describe an up and down movement of the surface of water (ripples) when something is dropped. The following sentences do not elaborate. So students may still not have a clear idea of what sound is. EGM and Kamajaya's books do not provide a satisfactory definition of sound. These two books begin by describing the source of sound as "a vibrating thing". To convince them, readers are asked to stick their finger on their throat while speaking, so they can feel vibrations. The limits of the auditory area are given as between 20 Hz and 20,000 Hz and EGM reminds readers that each person has a different threshold of hearing: for elderly people, the auditory band becomes narrow, and they may not be able to hear even the song of crickets.

1.2

The transmission of sound

At the beginning of the section on "the medium of sound" EGM states that "in order for sound to be heard, a vibration must reach the ears. So a medium for transmission is needed" (p.54). Similarly, Mangunwiyoto says "in order for sound to be heard, a medium which transfers a sound from its source to the ear is needed" (p.35). These statements are not entirely adequate answers to the question of why a medium of sound is needed. There is no attempt to relate a longitudinal mechanical wave and the medium of transmission. The types of media of the transmission are mentioned indirectly, for example, "sound can travel through liquids as (EGM, p.54), "gases (air in general), liquids of sound" (Mangunwiyoto, p.35), or "in gases, sound wave is a longitudinal wave" (Kamajaya) There is no discussion of the differences in the velocity of sound in different media. There is also no explicit comparison of the velocity of light and that of sound. In relation to the transmission of sound at night, EGM says that as a consequence of the velocity of sound in gases being the square of the absolute temperature, in daytime sound will be refracted upward and at the night it will be refracted downward. Thus sound would be heard more clearly at night than in the daytime. A similar account is given by Mangunwiyoto. The three books take a similar line on the reflection of sound: "in the same way as with waves, sound can be reflected" 22

(EGM, p.58). This statement may lead students to believe that sound is not a kind of wave. All books define resonance as a vibration which follows another vibration. The condition for resonance is given as when the frequency of the two vibrations are the same or one a multiple of the other. However, they omit to say that something only vibrates with its own natural frequency. Thus, they do not give an adequate explanation of why resonance does not occur at any frequency. The loudness of sound which is determined by the amplitude of the vibration is presented in Kamajaya's book and in EGM. Mangunwiyoto suggests another factor: the distance between the source and the listener. None relate loudness to the transfer of energy.

1.3 The detection of sound

• •

EGM and Kamajaya's books discuss activity in the human ear when there is a sound entering the ear canal as follows: The outer part of the ear collects waves of sound and transfers them into the eardrum ... the stimuli, then, are transfered to the brain, and so we hear the sound (EGM, p.82). Ears change and increase the fluctuation of the air pressure to become a wave of sound. This wave, which has been received by eardrums, is changed into an electric signal and transfered to the brain (Kamajaya, p.61). These passages do not give any indication of how the eardrums behave when sounds reach them, except that eardrums transfer the sound to the inner part of the ear or change the sound into an electric signal. Thus, they could lead to misunderstanding among students. The Doppler Effect is presented in a similar way. The mathematical approach is used. Students who try to solve problems using a diagram by placing the source to the right side of observer would find difficulty. Confusion may also occur if students use the usual convention of the positive sign for the movement to the right and the negative sign for the movement to the left. Summing up, there are many inappropriate explanations presented in Indonesian text books, which may contribute to misunderstandings. 23

2. Teachers' knowledge of the physics of sound It is rather difficult to examine teachers' knowledge directly by administering a set of tests. Not only did the investigator lack the authority for doing this but also teachers could be unwilling to take part in an exercise which might reveal their inadequacies. There were several physics teachers enrolled in an inservice training program who were willing to participate in the investigation. They were seven junior high school teachers and five senior high school teachers. It is believed that this sample may not be a representative sample. However, they share common academic backgrounds with their colleagues in that they did not have major studies in either physics or physics education. Nine common students' ideas which are reported in Section 3.3 were given to the teachers for comment. Teachers' comments then are examined in the following sections. 2.1 The generation of sound Most junior high school teachers agreed with the students' ideas that "sound can be generated by striking one object with another". This explanation is correct, but it should be remembered that there are many other sources of sound such as flute, trumpet, or musical stringed instruments which can produce sound without being struck. (Teacher no.2). Sound is the result of vibration ... it is not because one thing strikes another. (Teacher no.6). One of them gave a rather different comment. “Although we may strike a table powerfully, the sound would not be heard clearly if the listener is very far away. (Teacher no.7). All the senior high school teachers believed that striking one thing on another will cause vibration, and a vibrating object will produce sound. There were many explanations of the limitation of human ears to detect sound. These were: the distance between the source and the listener, and the human ear itself. There was, however, no attempt to relate to the sensitivity of the ear, the frequency of sound, and the sensitivity of age. 2.2 The transmission of sound 24

Only one of the junior high school teachers disagreed with the student's idea that sound is carried by waves which is similar to a “person being carried by a bus".

•

•

•

His comment is: “If the transmission of sound can be viewed as a person who is carried by a bus the medium of sound would move from one place to another. This is not true. Particles of the medium vibrate rather than move from one place to another”. (Teacher no.5) Although they believed that sound is transmitted as a wave, they believed that sound can be separated from the wave. The wave is a carrier for sound. Only one junior high school teacher agreed with the statement that "the velocity of sound in air is hiqher than in the water “because air particles are freer to move than water particles". Although the others did not agree with this students' idea, their reasons were varied. For example, teacher no.8 suggested that the particle movement is not a factor which influences the velocity of sound, and teacher no.ll believed that the energy of sound in water is higher than in air. All teachers disagreed with the similar belief that "the sound of thunder which is heard on the earth consists of several similarsounds produced by successive collisions in the air". It is not successive collisions but it is a sudden air explosion due to the electric charges as they move from one place to another. (Teacher no.8) One junior high school teacher agreed that "increasing the loudness of sound will increase e the velocity of the sound, because a loud sound can be heard far away", Others believed that loudness is correlated with amplitude and the distance between the source and the listener. This students' idea may be based on their experiences in everyday life. The louder its sound the higher is the speed of a motorcar. The sound of a supersonic aero-plane is even louder than an ordinary aero-plane". (Teacher no.9) Two junior high school teachers did not fully agree with the statement "because there is no sunlight at night sound can be heard from far away". It is not completely true .... It depends on the nature of the source of the sound. (Teacher no.7) 25

•

At night, air particles become close to each other. It is known that the closer the medium is the more difficult it is to pass through it. (Teacher no.6) All senior high school teachers agreed but they gave further explanations which were similar to scientists' conceptions. They related sunlight to the air temperature and the transmission of sound waves. 2.3 The detection of sound All teachers accepted the first sentence in the following statement "the sound of a siren will qet louder and hiQher as an ambulance is_aaproachina a listener. This is because the number of air particles which have to be passed through decreases". There were several different comments on the second sentence such as • It depends on the loudness. (Teacher no.7) • It is due to the increasing velocity. (Teacher no.3) • It is because the distance becomes less and less (Teacher no.2)

• • •

No one of them explained the effect of the movement of the ambulance on the frequency of the sound that was heard. Most teachers did not agree with the statement that "when a sound wave reaches the eardrum the eardrums will vibrate". They believed that vibration of the eardrums is due to resonance. The eardrums resonate to the incoming sound. (Teacher no.2) A similar comment was given by teachers no.3, 4 and 7. Other teachers viewed things differently. It is because the sound wave presses the eardrums back and forth. (Teacher no.5) The energy of the incoming sound vibrates the air particles inside the outer part of ears, they transfer this energy to the eardrums. (Teacher no.ll) In summary, there are some differences between teachers' conceptions and scientists' conceptions. This is likely to be due to their comparatively limited educational background. Only one of them had graduated from the Teacher Training Institution (IKIP) with specialisation in physics and mathematics education. The others had graduated from colleges or even General Senior High schools (SMAs), without physics courses as a major subject. However, because of the lack of physics teachers they are 26

expected to teach physics at their schools. This is how they came to be enrolled in the in-service program.

3

Students' pre-conceptions about sound

There are many approaches which can be used to prompt students' knowledge. However, because the method of investigation was based on half-hour recorded interviews and the focus of the investigation was students' pre-conceptions prior to instruction the Experiential Gestalt of Causation (EGC) approach was used. There were ten topics related to sound chosen for investigation. These are the generation of sound, the transmission of sound, the medium of transmission, the velocity of sound, light velocity vs sound velocity, the night phenomenon of sound, the sound of thunder, the loudness of sound, the Doppler effect, and the effect of the gravitational force on sound. The following sections deal with these topics. One hundred first year General Senior High School (SMA) students participated in this investigation. Subjects were chosen by their school principals. Thus it is understood that subjects are not equally distributed among schools, ethnic background, gender nor achievement. Based on schools' reports, the students could be grouped into high (29); medium (37), and low (44) achievers. Fifty-six students were male and forty-four female. Their fathers' ethnic origins were Chinese (38); Dayak (21) and Malay (44). 3.1

The generation of sound

The first part of the interview was focused on how students could generate sound, the relationship between sound and vibrations,and the limits of audible sound. There are two Indonesian words - suara and bunyi - which refer to sound. Suara is usually for living things (voice) and bunyi is for sound in general. However, many students used these words interchangeably. 27

I: P: I: P: I: I: P: I: P: I: P: I: P:

Some English translations are extracted as follows: (I:Interviewer, P: Pupil) How do you produce a sound? Knock a door or table. Another method? Rubbing one thing against another. What will happen if you knock this table? P: Sound! What else? ..(silence) Put your palm around here (on the table). I'll strike the table .... Do you feel that there's vibrations? Yes. Tell me the relationship between sound and vibration. ...(silence) Does a sound produce vibration or do vibrations produce a sound? Vibrations produce a sound. (Student no.99)

It seems that this student has some knowledge about how to generate sounds. Another student (no.91) tried to explain how to generate sounds by striking a table: P: There is a force. I: A force?! P: Yes. Because if I am striking this table I am applying a force to it. I: Do you believe that a force produces a sound? P: ...(silence) I: Put your palm around here (on the table). I will hammer this table .... Do you notice that something happens in your palm? P: ...vibration. I: Did your palm vibrate? P: ... my palm and the desk .... I: Is there any relationship between vibration and sound? P: ...(silence) I: Lets see .... Place this ruler on the edge of the table. Hold it firmly. Pull down the end of the ruler and let it go .... When the ruler was vibrating you heard a sound produced by the ruler, didn't you? Which one was coming first, vibration or sound? P: Vibration could be the first. I: Does vibration produce sound or .... P: Yes, it does. (Student no.91) At the beginning, he did not mention vibration, but after using several practical examples to prompt his knowledge it seems that he understood the relationship between vibration and 28

sound. There were many students who need to be prompted as these two students were. They also believed that there is a limit to audible sounds by saying that human ears are unable to hear all kinds of sounds. Some other students did not recognize this limit. The following extracts illustrate this point: I: Can we hear all kinds of sound produced by vibration? P: I don't know. We may be able to. (Student no.73) P: I really don't know. (Student no.57) P: It depends on our ears sensitivities. Some elderly people cannot hear sounds as we can. (Student no.88) The response of student no.88 is difficult to classify. It is not clear whether he really knows the limit of audible sounds or not. The following extract is also difficult to classify. I: How can you produce a sound? P: Striking anything strongly. I. Why? P: ... Because if I strike something strongly the air around this thing will be split. A sound will occur when these air layers collide one against the other. (Student no.57) All responses fell into two groups. The first group consists of students' responses which indicate that sound is generated by vibration (77%). The second group consists of those which do not (23%). 3.2 The transmission of sounds The following conversations were dealing with the transmission of sound. The conversation was started, usually, by asking whether or not the student could hear a sound which came from outside the room where the interview was being conducted.

29

Figure 3.1 A model of the transmission of sound The interviews reveal three types of students' ideas. The first group believed that sounds travel as waves (7%). The second group believed that sound is carried by waves (57%), and the third group believed that sound is carried by wind (36%). Some students' explanations are difficult to classify. 3.3

The medium of the transmission of sound

Some students believed that sound can travel through air and water but not through solids, because "there is no air in solids". There are other students who believed that sound can travel through either air (gases), water (liquids) or wood or iron (solids). Thirty-six percent of students believed that sound can only travel through air. Twenty percent believed that sound can pass either through air and water, and another twenty percent through air and iron. The rest (24%) said sound is able to pass through air, water and wood or iron as well. 3.4

The velocity of sound

Further conversation was focused on the velocity of sound in different media. This conversation was closely related to the previous conversation. For example, if a student said that sound 30

could pass through air and water as well, another question would be "In which medium is it faster?" Such a question was not asked of students who believed that sound can only pass through air. In general, students' answers fell into two groups: those who believed that sound moves faster in either wood or water than in air (53%) and those who believed that the opposite is true (13%). The rest, 35%, believed that sound can travel through air only. 3.5 Light velocity vs sound velocity The interview also covered the comparison of the velocity of sound and the velocity of light. Over half the students (55%) believed that the velocity of sound is less than the velocity of light. However, their explanations varied. 3.6

The night phenomena of sound transmission

Almost half the students (49%) believed that quietness (no competing noise) is the important factor in explaining why sound can be heard clearly from relatively distant places at night. Some students believed there was a combination of the effects of the quietness and the absence of the sun (20%), or the quietness and the coolness at night (19%), and even the quietness and the absence of wind (10%), on the clarity of sound at night. 3.7 The sound of thunder Seventy percent of students said that thunder consists of multiple collisions in the air which produces similar sounds successively. The first collision produces the loudest. 3.8

The loudness of sound

Almost all students (92%) stated that if the volume of a radio is turned up the velocity of its sound will increase. The reason is as given was 31

•

•

P: A loud sound can reach a distant place. So its velocity should be high. (Student no.17) Another student explained: P: A loud sound can be heard from further places than a weak (soft) sound. Everything which has high velocity can reach a distant place. Thus a loud sound should have a high velocity. (Student no.45) Five percent of students believed that the frequency of sound increases and only 3 percent of students said that the amplitude of sound will increase. None of them gave satisfactory reasons. 3.9

The Doppler Effect

When asked the question: "What happens if they are on the way home and were approached by an ambulance with the siren operating", most students (72%) said the loudness of the siren increases. Other students (24%) believed the frequency of sound will increase. Only a few students (4%) believed that its frequency will increase as well as its loudness. 3.10

The effect of the gravitational force on sound

The final stages of the interviews investigated the belief that gravitational force influences the transmission of sound. Seventy-two percent of students have this belief. Summing up, ten concepts related to sound phenomena have been investigated amongst students who were yet not enrolled in physics classes at General Senior High Schools in West Kalimantan. The results indicated that most students held different ideas from the scientists' ideas. Table 3. 1 Percentages of students who held different ideas from scientists' ideas related to sound phenomena 32

Phenomena

. . . . . . . . . 0.

Per cent

The generation of sound

77

The transmission of sound

93

The medium of sound

76

The velocity of sound

88

Light velocity vs sound velocity

55

The night phenomena of sound

90

The sound of thunder

70

The loudness of sound

92

The Doppler Effect 72 The effect of the gravitational force on 72 sound

As seen in Table 3.4.2, χ 2 tests show that students of different levels of achievement have different ideas about the transmission of sound, the medium of sound and the night phenomenon of the transmission of sound (at the 5% level of confidence). Boys and girls differed in their ideas about the night phenomenon and the sound of thunder (at the 5% level of confidence). Ethnic groups differed in their ideas about the loudness of sound (at the 1% level of confidence). Table 3.2 Distribution of χ 2 values of each sound phenomenon by students' achievement, gender, and ethnic group Pheno menon

No# 1 2 3 4 5

Achieveme nt

Gende r

Ethnic

0.12

3.45

1.89

12.76* 13.07* 0.16 0.22

3.40 4.94 ` 4.23 0.03

0.80 4.55 2.50 1.78 33

6 15.59* 9.56* 6.62 7 1.55 5.23* 0.80 8 8.69 2.87 14.18** 10.84 9 5.85 1.67 ** 10 3.66 0.35 0.09 # Descriptions are similar to those in Table 3.4.1. * Significant at 5% level. ** Significant at 1% level. These findings suggest strong reasons to investigate students' conceptions about sound after being taught in formal instruction. As Hewson and Hewson (1984) noticed, students come to science classes with "theories about how the natural world works - less coherent, less precise, less extensive than accepted scientific theories" (p.3). Terry, Jones, and Hurford (1985) argued that these ideas "are not likely to change simply because pupils are exposed to teaching strategies in which they are given the physicists' expectation of the situation (p.162). The next chapter deals with the development of the diagnostic test based on the students' pre-conceptions as the instrument with which to investigate the students' conceptions after attending formal physics

Important terms textbooks are of great concern in West Kalimantan buku paket Energi, gelombang dan medan Buku Pelajaran Fisika untuk SMA The generation of sound as seen in the text The transmission of sound The detection of sound Teachers' knowledge of the physics of sound The generation of sound The transmission of sound 34

The detection of sound Students' pre-conceptions about sound Experiential Gestalt of Causation (EGC) approach The generation of sound The transmission of sounds The medium of the transmission of sound The velocity of sound Light velocity vs sound velocity The night phenomena of sound transmission The sound of thunder The loudness of sound The Doppler Effect The effect of the gravitational force on sound

35