Since we are calling October “Cartober”, all of our Challenge Friday challenges are related to cars and the simple machine wheel-and-axle. Each challenge during the month of October builds on the challenges from previous weeks. We are also in the middle of a Fairy Tale unit in our language arts classroom, so I wanted to find a way to combine Challenge Friday, Cartober, and fairy tales! The challenge this week: find out what makes cars go faster and build the fastest car possible!
We started by reading the classic story of The Gingerbread Man. We talked about the elements of a fairy tale that the story included, just as we had done for all the other fairy tales that we had read during the unit. The kids noticed something important about the ending of The Gingerbread Man – that it didn’t end with a “happily ever after” for the gingerbread man. They noted that this was unusual for a fairy tale because most of them have happy endings. This led us to the challenge.
I told the kids that we were going to rewrite the ending so that the gingerbread man does end up happy instead of eaten. We called it The Gingerbread Man’s Great Escape. I told them that they would have to make a car like last week for the gingerbread man to make his getaway, but they would have to make the car go as fast as possible, and they would have to think like a scientist to do it.
First we brainstormed ideas for things that could possibly make a car go faster. The kids suggested things like more weight, less weight, bigger wheels, smaller wheels, using Lego pieces with holes so that air could pass through easier, and using wheels that spin easily.
Next I told them that they should try any of those modifications to their car to find out if it really does make the car go faster. I asked them how they would know scientifically that the car was actually going faster. I asked, “Will you just watch and guess whether or not it’s actually faster? Is that what scientists do?” One student suggested that we record something. I asked what exactly we would be recording. Several students shouted out, “Speed!” I asked them how we would do that. “What device do we have that records speed?” They couldn’t think of anything. Another student suggested that we could time the cars as they go down the ramp. Again, I asked what device we would use for that. We ended up using the stopwatch feature on the iPod touches.
The last conversation topic that we had before we started building and racing was about the idea of changing only one variable at a time. I asked them what would happen if they added weight, put on bigger tires, AND used a piece with holes, and the car went faster. How would they know which thing made the car go faster? They realized they wouldn’t be able to tell. So I reminded them to change only one thing at a time and then record the time before trying out another idea. I gave them each a little Lego gingerbread man figure to put on their car to help him escape from the fox!
The kids set to work right away and tested out ideas, recording the times as they went. It was interesting that many of them still had misconceptions about what exactly they were recording. Some would come to me and show me the time on their stopwatch and say, “Look at the speed now!! It’s way faster!” They were equating time with speed. Others needed help understanding what “1.6” means as a number.
Finally we met in a share circle to explain our results and conclusions to the rest of the class. Most kids came to the conclusion that adding more weight made their car go faster. A few came to other conclusions. We talked about the adding more weight and what effect it has on a car. This was an important idea because it has to do with their final challenge of the month. Then they recorded their conclusions on a reflection sheet that they glued into their notebooks.