Miha Lee
Dr. Foley
SED 690
October 10, 2007
Children’s Idea of Gaseous State
Clinical interview is an important skill in assessing the depth of conceptual understanding and the complexity of cognitive structure of learners. It helps the researcher identify the relevant conception children holds and the perceived relationships among those conceptions to ascertain the nature and extent of an individual’s knowledge about the particular domain (Posner & Gertzog, 1982). Therefore, it is also called ‘conceptual interview.’
Bearing this concept in mind, I performed a clinical interview to explore children’s conceptions about gaseous state. The interviewees were my own children: one (S1) is a 4th grade boy and the other (S2) is a 7th grade boy. For better communication, we used Korean as a main language for this interview. Even though the protocol was the same, I interviewed them separately so that their results should be independent from each other. But many parts of the responses were very similar, and thus I indicated these responses with ‘Both S1 and S2’ in the transcript.
To set a stage for the interview, the children were presented with three demonstrations carried out by me. These activities are focused on the basic physical properties of gas: its volume, pressure, and temperature. While the topic of gaseous state requires fundamental understanding of molecular dynamics in order to explain the behaviors of gas, the interviewees have not had the instruction required. Thus, the interview was used to probe their understanding of the gaseous state. Before, during and after demonstrations, I asked them many open-ended questions, and their responses were analyzed carefully to find out what they understand and how they think of gas.
To begin with, I introduced a topic by showing them a demonstration with a glass full of water. At first, I upside-downed the glass so that water fell down. When I asked them to explain why the water had come down from the glass, they told me that there was the gravity that was pulling down the water. Their responses were exactly the same as I had expected. Then, I challenged them with more complicated activity. This time, the glass of water was covered with a piece of aluminum foil, and when it turned upside-down the water still stayed in the glass (Figure 1). They were both surprised and puzzled. Their explains about the activity were worth describing.
S1 (4th grader) – Maybe the gravity that pulled the water down has disappeared.
I – Why does the gravity vanish this time?
Both S1 and S2 (7th grader) – I mean the effect of gravity has vanished.
I – Then what made the effect of gravity disappear?
S1 – I don’t know.
S2 (7th grader) – Something should pull the water up to cancel the effect of gravity,
but I don’t know what it is.
I - What’s the difference between the first one and this one?
S2 – Only the aluminum foil is the difference.
I – Can you tell me how the foil keep water inside of the glass?
S2 – The water is so stuck to the foil that air outside can’t go into the glass
to push the water out of the glass.
I – What makes the foil stuck to the water? Do you think water is that sticky?
S2 – I don’t think water is that sticky, but I can’t explain why both the foil and the water
don’t fall down this time.
I – Then, how about the outside of the glass? What is surrounding the glass?
Both S1 and S2 – Air! But there was air in both cases.
S2 – Air always pushes downward like the gravity, but the glass is protecting the water
from the air pressure. However, there is still the gravity that pulls the water down.
I can’t make sense of this.
I – Don’t worry. This question was very difficult. But we will be back to this problem
at the end of this interview. From now we are going to talk about the gas that is air surrounding us.
The demonstration I introduced was a kind of discrepant event that gave my interviewee the need to know about the gas. However, they just focused on the inside of the glass and the foil, not the outside of the glass, that they didn’t realize the root cause was the atmospheric pressure of the gas. Actually, this event is tricky enough to be used for even college level students to probe their understanding of air pressure, but the point I’m making is that the children were not conscious about the existence of air and their actions in normal situation like this event. Only when I told them to think about the surrounding air, they started to consider the presence and effect of air. From my teaching experience, I have learned that because air (as a gas) is invisible and very light (almost treated as weightless), young students have difficulty understanding the behavior of air. The other thing to notice is that the 7th grader mentioned the balanced force to cancel the effect of gravity, but he didn’t understand that surrounding air pushing the foil upward was the opposite force. In his mind, air pressure means the weight of air mass that exerts a force only downward like the gravity. It is common misconception that I have found from my students. To understand the phenomenon of atmospheric pressure, Kinetic Molecular Theory of Gases should be understood in advance. This activity let me know that my children don’t have a concept of gas pressure.
For the second activity in which I investigated the concept of pressure of a gas, I employed a Ziplock bag and an imagery balloon. I had prepared a rubber balloon, but my boys played with it and blew it off. Thus, I began the second section of the interview with demanding them to explain how and why they thought the balloon had blown off.
S1 (4th grader) – Brother(S2) tried to make it (the balloon) bigger by letting air go inside of
the balloon. But there was too much air going into the balloon, and it exploded.
I – Why did too much air cause the explosion?
Both S1 and S2 – There was not much space in the balloon. You know if air goes into a balloon, it exerts a force to make it bigger. So, too much air, too big balloon. That’s it.
I – How does air act a force on the balloon? Can you elaborate on that? You can draw a picture for me.
Figure 2. 4th grader’s drawing Figure 3. 7th grader’s drawing
Both S1 and S2 – (Showing their picture in which the air pushed the wall in every direction like figure 2 and 3.) Since a balloon is composed of particles, if it is getting bigger and bigger with the more air coming, the distance between the particles is also getting bigger and bigger. Therefore, eventually there is a leak in the wall of balloon, and air comes out through the leak.
I – Good! You are telling me that the more air going into the balloon causes a force, the push against the wall of the balloon. But I don’t see how air pushes the wall. Let’s do another activity with this plastic bag. (I opened a Ziplock bag and enclosed a small amount of air to make it a bit inflated.) What’s inside of the bag?
Both S1 and S2 – Air.
I – How do you know there is air inside?
Both S1 and S2 – We can see it bigger than before.
I – Do you believe there is air surrounding us? How?
Both S1 and S2 – I can’t feel it right now, but whenever I am breathing deeply and making a wind like this (moving his palm toward his face), I can feel it.
I – OK. Then to feel the air in the bag, let’s push the bag. What’s happening?
Both S1 and S2 – It is changing its shape.
I – How about the volume?
Both S1 and S2 – Its volume doesn’t seem to be changed with push.
I – If you push it harder than before, what will happen? Why?
Both S1 and S2 – It will burst air off through the mouth. Like the balloon, this bag has the air molecules occupy the space. When you push softly a corner of the bag, it moves to other places, so the shape is changed, but the volume is the same as before. However, if you push it hard, there is no place to go, so it comes out, opening the mouth. That is how the air inside exert a force, I mean the pressure, toward outside.
I – You mean air is flowing like water when you push?
S1 – Right. Air particles don’t move by themselves.
S2 – Similar. But Air molecules can fly from a place to another place.
I – Will you describe the state of air particles inside of the bag or a balloon?
S1 (4th grader) – As I told you, they are in touch with each other, taking up the whole space. When there is no vacant space between their body and the wall of a balloon, they push its wall.
S2 (7th grader) – The air molecules are in motion and there is space among particles.
These moving particles create the pressure against the wall by collision.
This second activity was very informative about the children’s idea of gas. First, they knew the existence of air not only by its action or movement but also by its taking up space, the volume. When they were asked to prove its evidence, they spoke of the size of the bag’s volume. However, their concepts of volume vary with the age or the level of education. The 4th grader thought of volume as the sum of each particle’s volume. The 7th grader saw the volume as the space taken up by the gas particles including the vacant space in which they fly.
Second, although both of them knew air consists of particles that take up space and create a volume of gas, their concept of motion of particles was very different. The 4th grader confounded a gaseous state with a liquid state that had no vacant space among particles and its particles didn’t move by themselves. For him, air in motion meant not flying (translation) but flowing. He thought that air couldn’t be compressed because there was no distance between particles. In contrast, the 7th grader had a concept of gas by which gas was composed of particles in motion, and there was much space between particles. Nevertheless, his concept seems to be week that it is in the stage of conceptual capture, for he didn’t know that when an external force acts on a gas in a constant temperature, its volume decreases by reducing the distance between particles.
Last, when it comes to the pressure, the 4th grader did know the term ‘pressure’ but didn’t seems to understand its meaning. He confused pressure with force. Therefore, it is natural for him that the pressure of gas is created by only external force like injecting more gas into a container or pushing a closed container. On the other hand, the 7th grader seemed have a weak concept of pressure. He understood moving air particles create the pressure against the container by collisions, but he didn’t understand the relationship between volume and pressure of gas.
The last section of the interview was the investigation of the relationship between volume and temperature of gas. I used the same bag I had used in the second section.
I – Interesting! Then, let’s move on to the last project. I’m going to put this bag into the boiling water. Let’s watch it. (The bag was getting bigger.) Can you explain this phenomenon?
S1 – Air molecules start to fly away from each other because of the hotness.
S2 - Air molecules fly faster away from each other because of the hotness.
I – You (S1) said before air molecules don’t move by themselves?
S1 – Right! But when the temperature is getting higher, they begin to move by themselves.
I – How do you know that?
Both S1 and S2 – I read the book you had bought for us. It told me like that.
I – Wow. Before we wrap up this interview, would you explain why the glass covered with a foil didn’t let the water fall down?
Both S1 and S2 – I still don’t know. Maybe it’s because of air. But I don’t know how.
This time their explain was very simple and knowledgeable. Both of them saw the temperature as the cause of expansion. Surprisingly, both of them told me that the expansion of volume was due to the air particles moving away from each other because their motion was getting faster. They didn’t mention the change in the amount of air. This shows they understood the conservation of mass of gas. However, the 4th grader imagined that air molecules at a room temperature didn’t move, and only when they were heated they started to move. Also, both of them learned it from a book without any evidence.
In sum, this clinical interview provided me with an opportunity to get useful information about my children’s idea of gaseous state. I found out that more efforts are needed to differentiate the concept of gas from the concept of liquid and to refine the concept of gas about the pressure. This requires the concepts of particulate nature of matter, their movements, its relation with the pressure of gas, and the temperature as molecular kinetic energy. This information will help me to adjust my teaching to my students’ preconceptions. Besides, this interview informed me that the students at different grades have different level of conceptions. However, maturation alone does not seem to be sufficient to cause the difference. It seems to be important to help it by appropriate teaching (Driver, Guesne, Tibergheien, 1985).
Reference
Driver, R., Guesne, E., & Tiberghien, A. (1985). Children’s ideas in science. Milton Keyes:
Posner, G. J. and Gertzog, W. A. (1982). The Clinical Interview and the Measurement of Conceptual Change. Science Education, v66 n2 p195-209