You can look at science instruction through two lenses. The first, knowledge as unproblematic. It goes something like this: I give you information, you write it down, you now have the information. No problem. The earth is round. I've told you, you now understand.
Then, there's the second view- knowledge as problematic. Think of it like this: we've been constructing knowledge long before we took our seats in the classroom. We build this knowledge through experiences and observation. Everything about these experiences and observations would lead us to believe the earth is flat. It doesn't feel like we're moving. In fact, if anything seems to be moving, it's the sun. The earth doesn't feel round when we walk. Understanding of scientific concepts comes from facts, yes, but those facts need to be consistent with experience if we're to build conceptual knowledge. You learn the earth is round by observing how a mast comes into view before the ship, or view images from space.
Take this pulley experience. I've gone through life thinking I had a crystal clear understanding of how a pulley system worked. When it came time to explain this concept, I went out to the hardware store picked up a few pulleys, borrowed a rock climbing rope, and we were ready to go. In the video, you can see the first attempt fail. And, I had no idea why. I'm standing there thinking, "I increased the distance, what's the problem?"So we went back inside and pulled up a diagram online. We discussed it, made some observations, and determined that the major problem was that the load wasn't on a pulley. I even copied down a sketch of the diagram to take back outside. Even though I had the information from the screen, I still didn't have a surefire understanding of how it all worked. We went about reconstructing the diagram and only then, after combining the facts and seeing it in action, did I develop an accurate understanding of a block-and-tackle.
As I told the students, I'm new here. Looking back, it was a lot of fun figuring it out alongside them. When I set out to perform the experiment, I was positive I knew how it all worked. At the least, I can say I modeled exactly how knowledge can be mis-constructed, deconstructed, and reconstructed.
Finally, we were able to have the fun I intended to have right off the bat. We pitted a few bigger kids on on the pulley, giving the single student on the other end of the rope the mechanical advantage, and everyone had the opportunity to feel experience how simple machines make work easier.
Later on, after we played around for a bit to give the knowledge a little time to settle in; I began twisting the pulley. Even after five rounds of the same results, I was a bit surprised to hear a few students still predict that, "so-and- so's gonna win." After everyone got their turn, they all seemed to understand that no matter how hard you pull, you're not going to beat the mechanical advantage.
I'll admit to smirking a little bit just before I handed the load end, twisted up, off. I figured that would throw a wrench in this newly minted understanding. When this time, the experiment didn't work as it had previously, they were quick to point out that the rope was twisted. I was impressed at how quickly the drew that conclusion. It makes sense; I'm sure at one point or another they came across a situation like that. Whether it's a dog's leash or the garder hose, we've probably encountered this problem before. 
Thanks to Scott, the next day we played around with the concept of friction a bit more. A student from Mrs. Lewis' class suggested we try this experiment with the class:
The interlocking pages make the books impossible to pull apart. This unit has been a lot of fun to work through with these kids. I'm looking forward to moving on to motion and energy with them next week. Here's one more treat in the form of a study guide. A hard copy print out, the PDF and the PowerPoint can be downloaded at lewis5.org.
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