I introduced force to the sixth graders today. I gave them two pages of the textbook to read last night, with questions, to prepare them. They seem to have understood that material pretty well, and I went over it in the course of my mini-lesson. We listed all the different forces we could think of (pushing something, pulling it, magnetism, gravity, friction). One thing that confuses many people is the idea that if you throw a ball, once you let go of the ball, you are no longer exerting a force on it. So, we touched on that, and we decided that it is inertia that keeps the ball moving forward, and gravity that pulls it downwards. I introduced the Newton - basically just that it is a unit used to measure force - and how to use a spring scale.
Then I handed out the lab. I had prepared bundles of one, two, and three textbooks, tied with twine. The students pulled the books across the table using the spring scales and recording how much force was required to move the books. They did three trials for each quantity of books. I had never done this lab before, and I wasn't sure how well it would go, but it actually worked pretty well. Their answers aren't very precise, because the spring scales tend to wobble as you pull the books, but they still found a clear increase in the amount of force necessary to move the books, as more books were added.
Follow-up questions to the lab included predicting the force needed to move four textbooks (and explaining your reasoning), how could you increase/decrease the amount of force needed to move a given number of books, and the usual sources of error & new questions. They are not doing a lab report on this one, just filling out a lab handout. I've got 'em trained, though, because five or six kids asked me questions about how to write the lab report. They looked a little shocked when I said they weren't doing one for another week or two.
Brilliant moment: two different kids independently pointed out that how fast you pulled the books might make a difference. One raised his hand during the lab and said that he wasn't sure their results were right because they didn't use constant speed. Whoa. This is a kid who fools around constantly, someone who's been kind of a pain in the neck lately. It was a nice reminder that he is more than the sum of his behavior (I know that should be obvious, but after the fiftieth time you ask someone to pay attention, it's easy to start to see only the misbehavior). The other was a girl who suggested decreasing the speed as a way to decrease the force. Anyway, it will be easy to segue to F=ma given that they've seen that there is some connection between a change in speed and force.
Another good thing about the lab was that while it seemed really ambitious to me, it actually fit neatly into one period, with a small amount of time left over for discussion. This is good, because I'm being formally observed tomorrow, and I warned my principal that the lesson was a lot of material for one period. She understands that sometimes you need to be ambitious and then take a little more time to finish something if you need to, so it wouldn't have been a problem, but won't she be impressed when the lesson actually fits in one period, including a "share" --!
In other news, the kids are STILL typing their momentum lab reports. I cut them off from class time - we had to move on - but as a result, I have a dozen kids in my room at lunch every day, and it is going to take them forever to finish because they really only get about 15 minutes by the time they eat and come back upstairs.... *sigh* Sometimes, you just have to type something in school, to teach them how to make their work professional and to provide computer opportunities to those students without computers at home, but they are such slow typists!