Thursday, December 15, 2005

All that and an ice storm, too!

Every day is made up of thousands of moments. I guess that's obvious, but today was one of those days that felt like the sum of it's parts, no more, no less.

I started the day cleaning out three dozen beakers which had held hand soap, corn syrup, and canola oil. I'm having the seventh graders measure the mass and volume of different quantities of different liquids, to prove that density is the same for a particular substance no matter how much or how little you have. They didn't finish on Tuesday, and I didn't see them on Wednesday, and I did not get a chance to clean out the beakers until today (my kingdom for a lab assistant!). Soapsuds everywhere. Me on my knees by the artroom sink, which is designed for 3-foot-tall people to wash their hands in. Corn syrup is tenaciously sticky.

Fully half of the seventh graders did not turn in a first draft of their lab reports, which were assigned on Monday. Excuses ranged from "I left my backpack at home" (WTF?) to "my computer has a virus and I did it but I can't get it to school" (your computer has had a virus for months - even I know that - why would you even try to type your project?). I turned into evil-Mussolini-wicked witch-teacher-from-hell. This happens often with this class. I resolve to be more patient with them, to be nicer to them, but then I enter the classroom and it's something new every day, and I end up back in dictator-land. That's the only way we get anything done. The first drafts I've read so far are pretty good, though, so maybe we are starting to make some progress. And they were quite impressed when we poured all three liquids into one beaker and they formed very nice layers by density!

I was supposed to call the homes of all the students who didn't turn in their projects - I assured the kids that I would - but the office where we store contact info was locked by the time I was done with robotics and ready to turn to that project. So now I'm going to look like I am not good for my word, and they will think they can "get over" on me. Urgh. Not like I was looking forward to calling twelve kids' parents, but I needed to do it because I said I would.

Newton's Laws have really brought out the inquisitive side of my sixth graders. It's wonderful - they are asking good questions - but I still have to say, "Okay, that's enough for right now, we must go on, I'd like to teach the lesson I planned but I'll take more questions later." It's great to have kids posing thought experiments about friction-less worlds. One reason I wish I had a mentor is that I am having a hard time explaining or demonstrating to the kids why it is that slowing down is essentially acceleration in the opposite direction of the object's motion. I understand it, but I can't explain it to my mostly-concrete thinkers in a way that makes sense to them.

And here's another puzzle. I introduced the idea of the normal force - when you push against the floor or wall or an object, it pushes back on you - and the kids seem to get it. At least, they know when to draw it in force diagrams and the like. But one class today hit an existential wall: they just don't believe in it. And the truth is, I hate, "You'll just have to believe me on this one," but I don't really have a better answer. Help me out, readers - where does the normal force come from? How do I prove it to my sixth graders? What I tried today, which convinced some but not all, was pointing out that if you were to kick a bowling ball, it would really hurt your foot. Why? Because your foot applies a force to the ball, and the ball applies a force back, which causes you pain. And the harder you kick the ball, the more it hurts, because the ball "kicks back" just as hard. They liked this example, but some kids insisted that the pain in your foot comes from the fact that your foot hit the ball, period. No "normal force" needed to explain that! Similarly, walls don't fall over when you lean against them because they're walls - of course they don't fall over. I guess that's why it's called "normal" - it feels so obvious, we don't notice it. Help!

We focused on Newton's 2nd law today. I talked to them about the relationships between force, mass, and acceleration, and we went over several examples. Then I introduced the formula - F=ma - and a second version of it, a=F/m. I explained that these are two different versions of the same formula, and that they might understand it now but they would definitely understand why when they did algebra in a year or two. Then we did some practice examples, which they found very easy. In two out of three classes, kids raised their hands and asked, "But what if you want to find the mass?" So, I gave them an example problem and asked them to think about what the formula might be to find mass. In both classes, hands shot up and they figured it out! I had them give themselves a hand for having done algebra (I am always trying to de-mystify the "scary" parts of math & science, which are often the most lovely once you try them). I think they were really proud of themselves.

And then I spent ten minutes back in dictator-witch mode, when my last class of the day not only did not follow our school's hallway behavior rules, but then became quite resistant and difficult when I enforced them. It was another of those, "Show them who's boss" moments and very stressful, but at this point, I know how to do it. Luckily, once class started, they settled down, I settled down, and they proved to be the most inquisitive of all the classes. One girl, who is consistently very difficult to deal with, in part because she is very bright, spent the whole period complaining loudly about a headache - a headache which developed coincidentally just after I asked her to follow the same rules that everyone else follows.

I will post about robotics separately so those following that story can find it easily - but the crowning moment of the day was when I was lining up the robotics kids to go downstairs, and they were just starting to settle down, when a little mouse ran squirmingly along the base of the cabinets just a yard or so from my toes! I am not a shrieker, but I gave a little "Eek!" I gave out the rest of the Hershey's Kisses that I've been using (sparingly) as bribes rewards in afterschool (and at staff meetings) because we wouldn't want the mouse to get them......

So today was a little of this and a little of that.

11 Comments:

Anonymous Bill said...

One possible way to explain normal force--from webnotes from my wife's alma mater, Concordia College in Moorhead, MN (Go Cobbers). Yes their mascot is a corn cob:

Consider a person standing in an elevator that is accelerating upward. The magnitude of the normal force on the person exerted by the floor of the elevator is larger than
the magnitude of the weight force of the person.

Not exactly the best way to explain it because kids are likely to attribute (rightly so) weight force to gravity, and the elevator is moving, but two forces are at work.

This is the best I can do at the moment as I contemplate how I am going to get to the Bronx tomorrow when nobody at my school lives remotely near my home on the outskirts of Bushwick and a $40 cab ride is not an option. To make matters worse, our principal made a PA announcement that everyone needs to get to work on time, no excuses! I might have to call her bluff and call in anyway! I still believe they will delay a walk out like they did last time. Wish everyone luck!

9:24 PM  
Blogger ms. frizzle said...

Oh yeah, I'm calling in if there's a strike tomorrow. If it's still going on Monday, I'll figure something out.

9:26 PM  
Anonymous Chaz said...

Ms. Frizzle;



Another reason to go to the high school....You have a lab technician who sets up and breaks down the lab equipment!!!

10:55 PM  
Blogger asyb said...

The wall remains standing when I (at about 11o pounds) lean on it. If I keep eating the way I like to and become 110 tons, what will happen when I lean on the wall?

11:07 PM  
Blogger M. Gatton said...

What would happen if the floor didn't exert a force? Can they reason that out based on what they know so far about unbalanced forces? Or if the floor were exerting a force greater than their weight?

5:51 AM  
Blogger graycie said...

My idea (as a non-science, concrete thinker) is similar to m. gatton's. What would happen without the normal force? Line up a series of balls: bowling, ping pong, nerf, soccer, baseball, whatever -- and kick them. Without the normal force, would there be a difference? (I don't know enough science to know the answer to this, so I don't know if it's relevant -- I'm now interested, though.)

11:51 AM  
Blogger ms. frizzle said...

Oh believe me, we've done the thought experiments about what would happen without the normal force. In two classes, it made sense (or they were too shy to ask) and in the third, they still did not buy into the necessity for the normal force. Thanks for all the ideas, though!

8:23 PM  
Blogger Lord Zagato said...

i think of the normal force as the resistance of the molecules of the other object to tear apart. since water molecules are farther apart and has less attraction than solid molecules, when i push on the surface of water, i break the surface and the normal force actually comes from all the interface i make with water perpendicularly, this can also be called bouyancy, salty water having ions have a lot more attraction so it pushes back more (so we're more bouyant in salty water). if you overcome the normal force exerted by a wall for example and it has nowhere to go because it's firmly attached, the surface will chip away or crack because you've overcome the molecular attraction. hope i've helped ^_^

6:52 AM  
Blogger M. Gatton said...

I would agree with zagato that the next step would be to look at what's happening on the molecular level - that's what it took to get me to really accept the idea on more than just the "authority" of the professor/text, but I doubt that 6th graders are ready for that level of understanding.

8:10 AM  
Blogger Late Nighter said...

I remember something (sorry this is vague but maybe you can pick up where I am lacking) from 7th grade about force. I know I get the concept but could you somehow show that there is force in a wall if you compare one car driving into a wall at 40mph and two cars driving into eachother at 20mph? (i'm not even sure if that really works out correctly...BUT when i read your blog that was the first thing that popped into my head.) Plus it would be cool to show some crash-test videos :-D

9:39 AM  
Blogger ProfessorDog said...

(This is way late, and I doubt you're even checking comments on here anymore, but) No idea on the normal force ( don't comletely grok it myself), but I have an example that might help concrete-ize (if that's a word) the thing about slowing down being acceleration in the opposite direction: to slow down (and eventually stop) a ship, the crew has to reverse the engines. They even show it in the movie Titanic (although if you don't have a TV/VCR in your room, and you probably don't, it's probably not worth it to get a media cart in just to show five seconds of a ship stopping.)

11:16 PM  

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