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Introduction to inquiry experiments (seventh grade)

One day during class last year, a student raised her hand and asked me, “Ms. Bove, are we going to have a party in here?” It was shortly before winter break and many of the other teachers were planning parties.

I answered, “No, but we're going to do an experiment,” and what I saw on the faces looking back at me was not disappointment, but curiosity.

“An experiment! What is it?” someone asked.

What is it? To answer that, I need to tell you the story of how we got to the exchange above. At the beginning of the year, we started a series of experiments where density and buoyancy* were the science content ideas. We continued these experiments throughout the year, doing one every two weeks or so. In my view, experiments are central to understanding science, and genuine experiments involve asking questions and designing experiments to answer the questions.

For me, the whole series of experiments was an experiment, and my question was, “Can we do experiments that are genuinely student-generated and designed in a public school setting where we have multiple classes of 30 students?”

Below is the list of the experiments we did over the course of the year.

The golf ball in salt water
Ice in alcohol and water
Ice in soda, vinegar, alcohol, water, salt water.
Ice in a one liter graduated cylinder with alcohol layered over water (quad quiz)
Weigh water and alcohol.
Look at viscosity à drop the marble in water and alcohol
Freeze 300 mL water
Freeze 40 mL water
Mix alcohol and water – add ice. Pour in more of one, more of the other
Weigh 44 mL water, alcohol ice
Weigh 44 mL of oil (click to watch video)
Put ice in oil
Freeze 44 mL of oil
Put frozen oil into oil
Pour oil in with water and alcohol in a one liter graduated cylinder
Put vegetables into the graduated cylinder and see where they float: carrot, celery, apple, potato
Find the density of a carrot
Find density of 44 mL of carrots
Find the density of Murphy's Oil Soap by weighing and measuring, then pour into the graduated cylinder to test

It is not really the list that is important, what the experiments are, but rather how we got to these, how we came up with these ideas.

The “Ice in alcohol and water” experiment, the second on the list, is a good introduction to the process that emerged as my classes experimented with density and buoyancy. Here's what happened: At the beginning of class, I rolled out a demo cart with two plastic cups, each filled with clear liquid. There was also a container of ice. We had practiced prediction, hypothesis, observation, and inference on the first experiment, “The golf ball.” I wanted students to experience the enjoyment of being puzzled, then thinking, and trying to figure something out. I didn't want it to be too laborious and boring, so I had them make a quick diagram of the materials before we began, I had them label: clear liquid, ice ( click here to see student journal entries ) and a prediction in their journals, and an explanation of their prediction. (I wanted students to understand that we explain before and after the experiment, but I didn't want them to worry too much about the words hypothesis and inference. I didn't insist too much on the vocabulary. If they were focusing on the science problem, and hearing the words hypothesis and inference when they were in the process of generating hypotheses and inferences, then the vocabulary would gradually sink in.

I held up two pieces of ice and talked about why they were a funny shape, sort of half circles, because my freezer makes ice that shape. I wanted people to see that this is actual ice from someone's freezer – not some special “science” ice. After getting everyone's attention, I dropped in the two pieces of ice, one into each cup. In one cup, the ice floated at the top. In the other, it sank to the bottom.

Silence. In a middle school classroom, silence is something you notice. Then I asked if there were someone brave enough to try to explain. One student offered an idea, then another, and then another. Someone said maybe there is something wrong with the ice. I put more ice in, and we saw the same result. A consensus began to form that there was something “wrong” with one of the glasses of water. It must be something other than water, or something was in the water. Maybe it was soda, someone guessed, or salt water, or warm water.

I asked how we could find out what it is. It was kind of too obvious a question, and it took a while for someone to say that, well, we could try them. So I said, OK, next time we do this, I'll bring those things, and we'll test them. I wrote down a list of all the things they wanted to try. And for the next time, I brought what they said: soda and hot water, salt water and vinegar.

During the course of this series of experiments, one thing I kept doing was to go away and think about how to frame the next experiment. And I had to do that this time.

This next part is partly a confession, partly a carefully thought out teacher move. If you are a teacher, and if you try this yourself, you'll have to decide where you stand on it.

No one said alcohol. So when I brought the liquids, I brought alcohol, and I said that some of these ideas are from our class and some are from the other class.” Which was almost true, except that it was a class from a different year that someone had guessed alcohol.

The reason I did it this way, instead of using strictly what they said, is that I wanted them to experience the feeling of generating ideas, and I also wanted them to experience having one of the guesses actually work. To avoid leaving the experience as one of frustration and defeat. I sometimes nudged things in a direction I thought productive without actually telling or leading. This was a general problem each time, because, at times the classes sometimes generated the same ideas, and at times, different ones. So I would occasionally say, “someone in the other class said…” I felt OK about doing it this way because each thing really was a student idea. The reason my conscience allowed me to do this was that these were all student-generated ideas. And I didn't push beyond the understanding of the majority of the class, or the middle of the class.

What does it feel like when one of the ideas, yours or another student's, actually works? That is what I wanted them to know / experience.

From that jumping off point, where we tried to determine what was “wrong' with that second glass of water, we started to build up an intuitive, experimental definition of density. We thought about why the ice sinks in the alcohol. Someone said maybe it is heavier, and I asked how we could test that? A number of people said “weigh them.” One student remembered the experiment we did in sixth grade about viscosity, and wondered if it had to do with viscosity. (Later on, we tried an experiment to see if there were a direct relationship – and then, much later, when we determined that there was not, we tried an experiment to see if there were an inverse relationship.) All this time we were weighing things and measuring their volume and seeing what would float on top of what – oil on water, water layered under alcohol, ice in oil, carrots and celery and apples in a tube with oil and alcohol and water. Gradually, students built up a sense that when something weighed more, for the same volume, it would sink to the bottom.

We took 40 milliliters of water and froze it, and got 44 milliliters of ice. Then, we compared it to 44 mL of water, of alcohol, and later of oil, and of carrots. As we went along, we tried to explain, and the idea of thickness or solidity kept coming up intuitively as more dense, but then when we weighed and predicted, we got it right.

For me, as the teacher, I kept getting stumped by things that would happen in these student generated experiments. For example, the first time we weighed water, ice, and alcohol, we had students doing it in front of the class, and their numbers came out wrong - we got that ice was less dense than alcohol. I wasn't sure what to do, because I didn't want to say “your numbers are wrong, that's not what you are supposed to get!” What I decided to do was to have people measure in pairs – so we would have a number of runs and we could look at sixteen sets of numbers instead of just one. So the process was one of their generating ideas, and my trying gently to keep us on a productive path as they moved forward in their understanding.

The very last experiment we did in this series was to test the density of Murphy's Oil soap. (It was only last because we didn't have time to do more – I was way behind the other seventh grade science teachers in the lessons of our shared curriculum.) Students kept coming back to the idea of viscosity and density, after the experiment in the sixth grade where we investigated that. Oil was viscous but not dense. So we came up with the idea of testing the most viscous liquid from that other experiment “The Viscosity Experiment,” which happened to be Murphy's Oil Soap, a liquid with a viscosity similar to corn syrup. Click here to see that experiment. We weighed, and collected date, and averaged – then I poured the soap into the one liter graduated cylinder we were using to test the buoyancy of each substance. At this point, everyone knew that the numbers we got predicted a certain result in the floating and sinking experiment: our numbers showed that if the soap were more dense, it should sink to the bottom of the graduated cylinder, the column with the other liquids in it.

Over the year, we made predictions, we saw what happened, we tried to explain, and we thought of new things to try. We weighed, measured, dropped and poured things into the graduated cylinder together. We looked at numbers and compared them to the behavior of substances. As a result, students developed an understanding of the relationship between the numbers we measured and the floating behavior of the substances. It was no longer magic: it was measurable. And they developed an understanding of how to do experiments themselves.

* Seventh grade teachers in California know density and buoyancy are not in the standards, but the experiments are in the Investigation and Experimentation standard. And density and buoyancy lend themselves to experimentation.

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