I was operating in a state of exhaustion this week, and didn't even write out a lesson plan. Fortunately Newton's second law is pretty straightforward, so it was pretty easy to wing it.
I started by defining force, mass, and acceleration, writing each word on the board and then discussing. For "force" I pushed on various things (the wall, one of the kids, etc.). Easy and obvious. For "mass" I explained that it was little more complicated, but it has to do with how big and heavy something is BUT it isn't exactly that -- it's more along the lines of how much STUFF (matter) something has. I had a styrofoam cooler and a black ice pack -- the black ice pack was smaller in dimension, but weighed more while we're standing here on Earth. I chose those objects, by the way, because they I saw them in my house while I was pondering how to explain the concept. For "acceleration" I talked about the accelerator on a car and the acceleration lane on a highway. I also explained that scientists have much more precise definitions of these things that take direction into consideration, but we weren't going to worry about that now since we're just after a broad picture.
Next, some hands-on examples of the concept of Newton's 2nd law. We talked about how easy it was for H to zip that Barbie car across the floor in last week's class, and tried to picture how tough it would be for her to push MY car across the parking lot. That's an example of a greater mass needing more force to move it and attain the same acceleration. Then I whipped out a slingshot and pulled it back just a little to send a pingpong ball going a short distance; next pulled it back more so the pingpong ball bounced off the opposite wall and halfway back across the room (this was wildly popular) for another example of varying force, but this time holding mass constant so acceleration became greater. Finally, to demonstrate 2 different masses reacting to gravity, we did the ever-popular impact-crater demonstration, which oddly enough not one of the kids said they'd ever seen -- I put flour in a cake pan, covered it with a layer of cocoa, set the entire thing on a drop cloth on the flour, then dropped a pingpong ball and a golf ball in it at the same time. I explained to the kids that I hadn't tried it at home, but my hypothesis was that the golf ball would hit harder and make a bigger crater (again, this was wildly popular in that I admitted that I hadn't tried it out ahead of time -- plus the way the flour poofed all over our shoes -- I let one of the kids try it a second time, then fielded about a zillion questions about whether we could bake a cake in class sometime).
Next, I wrote out a simplified version of the law on the board and had them copy it onto a piece of paper for their booklet of Newton's Laws: The acceleration of an object depends upon its mass and the applied force. The kids who were stunned and horrified by the copying-off-the-board concept last week seemed less so this week.
After everyone had finished copying, I erased the board and wrote F=MA, which I explained, emphasizing that it was an incredibly important math equation, and that their parents would probably recognize it if they went home tonight and said they had studied it today.
Some of the kids were asking if they were going to draw something on their papers again this week (last week I had them draw or write about one of the demonstrations we did). I said they could use the space to design their next project it they wanted. Because we were going to apply our knowledge of force, mass and acceleration to CATAPULTS. I used AmiMental's blog post for my inspiration, although I tweaked it a bit (homeschoolers tweak everything, it seems), using slightly different supplies.
Really, I should've added "measuring tape" to the list of supplies -- as kids finished their catapults they lined up and shot them off. We laid popsicle sticks on the floor to show where the various cotton balls hit.
I pretty much joined them in the building this time, helping kids who were drawing a blank on how to go about this to brainstorm ("hey, how about if we do THIS", or "do you think it would help if you added something here?"). Some of the boys built slingshots, claiming that they were a type of catapult. Um, not really. But I also said we'd probably be doing more with catapults later on when we get to machines, so I just sort of rolled my eyes and moved on.
Many of the kids handed in their creations at the end of the class period. I wrote their names on them, and plan to save them for our Open House display later in the fall.