予想討論の後実験しようﾊﾝｶﾞﾘｰ9707

International conference of Physics Teachers, Sopron,Hungary 1997
2001 International Conference on Physics Education in Cultural Context, Chengwon, Korea 2001

"LET'S MAKE AN EXPERIMENT AFTER EXPECTATION AND DISCUSSION!"

-THE CLASS DEVELOPED BY DISCUSSION-

YOJI IIDA

Nagoya Tomida (Sakuradai) High School, Nagoya, Japan

[Ⅰ] The conditions for discussion

At Japanese high schools, not only the class of physics but also almost all classes are conducted with "knowledge-packing system." The class of physics through the process of discussion and experiment are not so commonly conducted. Quite a few teachers would like to conduct such classes developed by discussion. But it seems rather difficult for them to get the result as they expected. In my classes, some questions can cause the active discussions, but the other can't.

We need some conditions for the discussion.

The discussion would be active and attractive when the question has clear confrontation between the logic of experience and that of science. And the experiment after discussion will become more impressive. According to my experience for about 30 years, the questions of "dynamics"; especially, the law of inertia and force and motion which have been thought to be the dullest studying field can cause the active discussions. That's because it's easier to make such questions in dynamics which has clear confrontation between the logic of experience and that of science.

The method like this is very effective in forming a concept. I have learned much from K. Itakura's "Hypothesis-Experiment Instruction Method," 1963 and K. Shoji's "Three Stages of Expectations," 1976. They applied to a practical teaching method M. Taketani's "Three Stages Theory of Recognition," 1936.

(1) Is it the question which is wanted to discuss naturally?

There are two kinds of questions, one is the question which students want to discuss voluntarily as soon as they see it, and the other is not such a question. The question whose contents students like to discuss voluntarily can surely cause an active discussion.

Such questions satisfy the following conditions at least.

① The confrontation is clear between logic of experience and that of science.

② Some of experienced and learned knowledge can be used as judging materials.

③ Student's own logic can be used.

Therefore, the important thing is not how to make students discuss, but how to make such questions that have clear confronting points and cause voluntary discussion. Moreover, it is necessary to examine their preconception and misconception, at the same time, to reconsider the concept of science, referring to the law of the development of recognition.

(2) Is there the atmosphere where students can express their opinions freely, even if they make mistakes?

The discussion is surely affected by the atmosphere in the class very much. It is difficult and needs some courage to express in public opinions which may be wrong. The students will find it more and more difficult to express uncertain opinions, minding of being laughed at for saying strange things.

Japanese ordinal students would think so. Anyway we, teachers, must make much effort in order to get rid of their first feeling of resistance against the discussion. "Don't be afraid of making mistakes", I always say to my student mentioning some examples in the history of science.

It is better to form groups consisting of 4 or 6 members in order to make students speak easily. The role of the leader of each group is to help the group's member to speak freely.

After each member finishes expressing his opinion, the distribution of expectation should be written on the blackboard and the whole discussion of the class should be started.

The students will express their opinions at almost all classes, if they find that they will be welcomed without being laughed, even when their opinions are wrong.

(3) For discussion, are there any experiments with conclusion which can be judged to be right or not?

Because their expectation are verified by the experiment, anyone can not help watching the process of the experiment with their heart beating in excitement. The experiment like this is more effective for the discussion. The simple experiment would be better than the complicated one. In fact, however, such an experiment is very difficult to develop.

(4) For the concept-formation, it is necessary to pile up the series of many questions and experiments following the development of student's recognition.

[Ⅱ] The examples of questions and experiments which can promote the discussion

The following is the first question in my class of dynamics which can develop the active discussion among my students every year without fail.

[ Question 1 ]

When a bead is dropped along the different slope, from the same level of height, which is faster, A or B, at the point of P?

<Expectation:>

　　　 (a) VA > VB

　　　　　　　　　(b) VA = VB

The distribution of some class was as follows:

Students write and display all the expectations of each group on the blackboard and change them with arrow marks freely, if the expectations are changed through their discussion.

Group　　1 2 3 4 5 6 7 8 9 Total

(a)　　 0 3 0 0 0 0 1 1 0 5→ 3

(b)　　 2 0 4 1 3 2 0 2 1 15→17

The main opinions expressed during these several years are as follows:

The opinions are rich in variety, but they are all based on some logics, experiences and learning.

-The steep slope makes the speed faster.

-The steep slope makes the bigger energy.

-B is faster, because of shorter distance.

-The steep slope has less friction.

-The experiment using a pencil showed that B was faster.

-In the case of longer distance, run-up can be made more.

-On the longer slope, the speed can be accelerated for a long time, accordingly the speed is made faster.

-When going down the long and gentle slope by bicycle, the accelerated speed could be too fast to control.

-As the height is same, the longer distance makes A faster.

-On the longer slope, the rotation of the bead becomes more and the speed becomes faster.

-The formula shown in the textbook of Junior High School is maybe like this.

-A has longer distance but it has gentler slope, so the speed is same.

-Both A & B have the same weight, so they drop at the same time.

-If the opinion of (a) and (b) just contradict each other, the speed will be same after all.

-Suppose there is no friction, either slope will not be different, getting the same force.

-A pendulum will go up to the same level, if it is dropped from the same level of height. So if the height is same, the speed is same.

-Being against the opinion (a), if the degree of the slope is same, the speed will be faster in the longer distance.

-In the case of same height, the kinetic energy as well as the potential energy is same.

-I noticed that the opinion (c) is not correct. I misunderstood that the bead arriving at P point faster would be more speedy.

The experiment is done with "THE SPEEDOMETER indicated by Hitting" (as called by me). As illustration, I make the slope, using a plastic molding with 凹 in the center, and attach it on the blackboard. Only comparing the speed with each other is quite easy. You have only to hang the cap of a empty bin at the tip of a scale.

First, set the cap in order that the bead dropped from slope B may hit it.

Next, if the bead dropped from slope A hits the cap, too, it means the speed is same. If the ball dropped from slope A jumps over the cap, it means that A is faster. If it drops front side of the

cap, it clearly shows that A is slower.

Now, let's start this experiment!

First, make the bead from B hit the cap and after that drop the bead from A. It hits successfully. "Made it!" "Why?" Surprising shout will surely be heard from both sides the group against and the group for. The voices such as "That's funny." or "The way is wrong." may be also heard. Repeat the experiment several times, but the bead from A will hit the cap.

The next question following:

[ Question 2 ]

This time, the slope A is made for the bead to go up and down from the height of the point P. Which is faster, A or B, at the point of P, when the bead is dropped from the same height?

<Expectation:>

　　　 (a) VA > VB

　　　　　　　　　(b) VA = VB

<Distribution:>

(a) 13→11 (b) 21→24 (c) 5→4

-Being set lower, the distance becomes longer, so the speed will be faster that much. (a)

-Because of going up, the speed will be decreased. and moreover, the friction also makes the speed slower. (b)

-If the height is same, the speed is same this time, too. (b)

-Going down makes the power bigger, and the bead will go over the horizontal point. (a)

-Going up and down at the same degree makes no difference in the speed. If the height is same, the speed is same this time, too. (b)

As this experiment was done after [Question 1], the opinion that the speed of A & B is same increased truly as expected.

Now, the experiment started! Again the bead hits! A stir also happened again. Well, then, how about the experiment with "Jet Coaster"?

[ Question 3 ]

The slope A is made with a jet coaster on which the bead can turn round. Which is faster, A or B at the point of P, if it is dropped from the same height?

<Expectation:>

(a) VA > VB

(b) VA = VB

<Distribution:>

(a) 7→8 (b) 28→27 (c) 5→5

Usually, at this stage, the opinion that if the height is same, the speed is same increases overwhelmingly. But in some years past, rather many students changed their opinions to (a) after hearing the following strong opinion that turning causes a centrifugal force and the speed would be accelerated, so the speed would be different. Moreover, there is also an opinion like this that in the case of loop, the distance would be much longer and the affect of friction can’t be neglected, and so the speed would be slower.

The experiment was started again. The bead hits surely. "Is that true indeed?"

Through this kind of discussion and series of experiments, it will become clear that the speed of the dropping thing is decided by only the height, having no relation with any courses. Students will be confident that there is surely a law and everything happens according to the law.

If the hitting mark speed indicator is used, it can judge which is correct, exactly and impressively. In the past, the comparison of the speed through the experiment was very difficult. Though the recording timer was used for the experiment for some time, the timer can't compete with this method at all.

This speed-indicator can be applied to the following questions:

[ Question 4 ]

Well, if you want to make the speed of A at the point P twice as fast as B, how many times of height do you have to drop the bead A?

<Expectation:>

(a) 1.4 times　　　　

(b) twice

(d) others

<Distribution:>

(a)0 (b) 22 　　 (c) 15 (d) 2 (three times)

In order to confirm that the speed become twice as fast, you have only to extend the scale twice as long and examine whether the bead hits the mark (the cap) or not. To my regret, however, this question hardly brings about an active discussion. This is because it's difficult for the students to mention the reason for the choice from the standpoint of their experience and logic.

Referred to:

"IKIIKI WAKUWAKU" JAPANESE-HUNGARIAN PHYSICS TEACHER MEETING, 1992 P101～9

"RE-MAKE-UP OF MECHANICS viewed from the learner" jointly-issued by N. Mitsui, H. Kawakatsu and Y. Iida "Shinsei Shuppan" 1992