Here's an example of a lab we just completed.
First, I told the students that we were going to do an experiment--and that my question was "Will this ball bounce higher on the tile floor or the carpet floor?" The students rolled their eyes as if to let me know that this was SOOOOO ridiculously easy. I told them that I was glad they all had a hypothesis, and that I was going to conduct a very brief experiment and I needed them to observe. I assigned a student to take notes. I informed that that I would bounce the ball on each surface three times and we would observe.
Round one--dropped the ball from waist height to the tile floor. Bounced the ball full force on the carpet (like "took out a ceiling tile" full force!) CARPET WINS! Gasps escaped...complaints of "But you can't . . . "
I hushed the critics.
Round two--dropped the ball from above my head to the tile floor. Let it trickle out of my hand knee-height on the carpet. TILE WINS! Now the scientist were getting downright unruly! "That's not FAIR!" and other grumbles filled the air.
I held up my hand to stop them.
Round three--dropped the ball on the tile with a nicely timed spinning motion. Threw it underhand WAY up high before dropping it onto the carpet. CARPET WINS!
So . . . I announce loudly, " My conclusion is . . .balls will bounce higher on carpet than on tile!"
Pandemonium. I settled them down, and asked them innocently, "What's the matter?" Boy, did I get an earful. It was obvious that they understood that this was NOT a fair test.
Seemed like a good time to teach the following:
We discussed the concept of constants and variables, and I explained that I had another experiment to try. I wanted to know what would happen if I put a drop of food coloring in a jar of water . . . a lab we had already done to practice observations. (Pretty fun, by the way). I told them we were going to shake it up a little by trying to keep everything CONSTANT except one thing--water temperature.
We worked to make a list of all the other things we would need to keep constant.
Once we had it figured out, we decided on our plan, made our hypotheses, and tried it!
The students were SO excited. I sent them back to their desks to record their observations and write in their own words what "constant" and "variable" mean. Was it rocket science? Not really--but I think the point was made clear. We'll really reinforce the concept as we work through the rest of the unit.
(By the way--the point of this lab will come out later when we talk about particles in motion . . .)
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