Saturday, January 21, 2006

Life, and Simple Machines

I felt like I was on my principal's "sh!t list" for the last week or so - the deep freeze - really, ever since that comment about me being "condescending and insulting." As a result of that and other little things, I wasn't feeling too comfortable in my own skin at work. Ironically, despite all the distracting political junk, I think I'm doing some of my best teaching ever with the sixth graders, and it feels so easy.

And then yesterday, things seemed normal again with my principal. And it was 50-degrees and sunny, which is a little creepy in January, but I'm not exactly complaining... and I went to the most amazing yoga class, ever, challenging and joyful and absurdly fast-paced... and I couldn't stop smiling all evening, which is something that hasn't happened since... I can't honestly remember.

Anyway, I've been meaning to write a little about my unit on Simple Machines, which is so much fun and feels like I actually know what I'm doing in the classroom, and might be useful for someone out there trying to teach this stuff.

We segued from reading about work and power and practicing our non-fiction reading skills into simple machines. They were completely confused about the idea that machines don't make less work, they just make work easier by changing the force, distance, and/or direction. I gave some examples and then asked them to trust me, that we'd see it in action over the next few days, and to ask again if they were still confused after doing some exploration. They decided to trust. This makes me think of my headstand: some skills emerge from a bunch of playful explorations and a little explicit teaching.

For inclined planes, I set up three stations. I have six groups in my classes, so we had two of each station. It took two days to introduce each station and rotate through all three, about 25 minutes at each station. Then we took another period and just discussed what we learned. I had them read the textbook section on inclined planes for homework, and use their reading skills to "take useful notes." Most took pretty good-looking notes, though I only had time to glance at them.

The first station had them pull a block up a cardboard ramp to the seat of a chair. They pulled straight up, up a steep ramp, and up a gradual ramp, and they used a spring scale to measure the force needed, and a meter stick to measure the distance. The experiment was wildly imprecise but it consistently showed that the longer the ramp, the less force required.

The second station had them investigate screws. I put a bunch of screws in a tray, and asked them to trace the threads with a finger and draw the shape of the threads - a spiral. Then they took triangular shaped pieces of paper and wrapped them around pencils, to see that the threads are formed by an inclined plane being wrapped around a cylinder. I had two different triangles for them to compare, to see what kinds of threads are formed by a "steep" triangle and a "gradual" triangle. Then I asked them to predict which type of screw would require more force to screw into a board, and which would need to be turned a longer distance. If I do this station again, I will have them actually test their prediction with a screwdriver...

The third station made me very nervous, though the kids handled it extremely well. I had them look at wedges - doorstops and kitchen knives. They examined the shapes of these objects to see that they are inclined planes. Then they cut carrots and pushed the doorstop under the door, observing the direction of the input and output forces, to see that wedges take a force in one direction and turn it into a force in another direction. We use knives every day, but how often do you think that you are applying a downward force, and the knife is applying a horizontal force on the object you are cutting? I let the kids use pretty sharp knives - after all, they all have these things in their kitchens - but I kept close watch and set very clear expectations of how the knives would be handled. I think plastic knives and clay would work, though it would be a little harder to see the wedge-shape of the knife and to see the change in direction of the force.

Inclined planes are unique in allowing the middle school teacher to say "wedge" and "screw" about a hundred times a day and all in the same unit!

This week, post-test, we moved on to levers.

The first day, I introduced vocabulary: load, effort, fulcrum, and the three classes of levers. We looked a first-class lever by placing a marker under a meterstick as a fulcrum and a dictionary at one end as a load, and then pressing down on the other end to try to lift the dictionary. I had them start with the fulcrum very close to the load and move it closer and closer to the effort. They discovered that the farther you move the fulcrum from the load, the more force is needed. Then I put a beaker under the meter stick instead of the marker, to make it easier to see, and showed them that when the fulcrum is close to the load, you apply your effort force over a longer distance, and when the fulcrum is farther from the load, you only push down a short distance. The greater the distance, the less force you have to use. Note to teachers trying this in their classrooms: If you try to use the whole length of the meterstick, it bends a lot and doesn't really work. Put the meterstick on the table so that 0-55 cm are on the table, the rest off. Put the dictionary from 0-10 cm. Start with the fulcrum at 20 cm, then 30 cm, then 40 cm. Apply the effort at 50 cm.

The second day, I set up three stations. The first had to do with second class levers. I marked three points on the door A, B, and C. A was close to the hinges, B in the center of the door, C close to the doorknob. I had the kids try opening the door by pressing only at each point. It is pretty much impossible to open the door by pressing at point A, very difficult at B, and easy at C. They got a kick out of this because it was so dramatic, even though we open and close doors every day. Then I had them place chart paper under the door and hold a marker pointing downwards at each point. They traced the path of the door at that point, to see that at point A, the door moves only a really short distance, while at point C, it moves a much longer distance. Again, they explored the relationship betwen force and distance. I asked them to identify the effort, load, and fulcrum of the door, and to explain why doorknobs are located towards the outer edge of the door. One group asked me if lifting the cover of their binder was like using a 2nd class lever, with the rings the fulcrum, the effort applied to the edge of the binder, and the load being the binder cover itself.

The second two stations had to do with third class levers. One just asked them to try sweeping with one hand on the top of the broom and the other near the bottom of the broom, and then with the effort hand closer to the middle, and finally with the effort hand close to the fulcrum hand. For the second station, I had tied up a bundle of textbooks and hung them from one end of a meterstick. They were to hold the other end of the meterstick in place with their left hand, then use their right hand in the middle of the meterstick to try to lift the books. I had them investigate placing their effort hand closer to the load and closer to the fulcrum. Again, dramatic results: it is pretty much impossible to lift the books unless your effort hand is really close to the load.

Next week, we'll discuss levers a bit more, process what we learned, and make "foldables" (brochures) about the three classes of levers, then on to pulleys and wheels & axles.


I am loving Kelly Hogan's take on the Magnetic Fields' "Papa Was a Rodeo."


Anonymous Anonymous said...

Is my browser gone wonky or did you do a redesign? Regardless, I like the white background -- much easier to read!

5:49 PM  
Anonymous un-lurker said...

Good description of the stations and how you set them up. I'm stealing all of this. Downside - it sounds like a lot of stuff I'd have to buy with my own cash.

8:20 PM  
Blogger ms. frizzle said...

You probably have a lot of random stuff around to use - I found all the screws in my kitchen and toolkit, for example. String is inexpensive. Metersticks and spring scales are the most expensive part of this, and you will use them so many times, it might be worth the investment.

8:30 PM  
Blogger ms. frizzle said...

And email me (address in sidebar) if you want me to send you the materials I typed up for the kids.

8:30 PM  

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