OK, so, what the heck happened over these 15 days?
1) There's a better way to teach science than powerpoint lectures & cookie-cutter labs.
Granted, my powerpoints tend to be more interesting than a standard teacher's, thanks to my training thru the National Association for Interpretation (https://www.interpnet.com/). I'm not a super great interpreter like some of my former coworkers at the Kalamazoo Nature Center, but I understand the concept -- short, sweet, connected to real life. Doing is always better than listening or note-taking.
2) If you don't say it, you don't understand it.
Whiteboarding (& especially the discussions that follow) are a sneaky way to get kids to teach each other. "Why did you do that?" "Is there another way?" "I think you're saying this, but am I right?" Sure, they're learning how to work together & have arguments about the data, but they're also hammering out how physics actually works. (This is kinda how I learned algebra in high school -- I'd help a friend with homework over the phone. Talk about a challenge!) My warm-up questions almost always have an "& why" portion to them, so making the jump to whiteboard discussions hopefully won't be too hard. (Altho, granted, it will take some practice.) & just for fun: http://skeptics.stackexchange.com/questions/8742/did-einstein-say-if-you-cant-explain-it-simply-you-dont-understand-it-well-en
3) This workshop assumes you have the necessary equipment.
We used tons of Vernier equipment (http://www.vernier.com/) throughout this workshop, & we don't have any at my school. A few times Don or Laura said, "Well, you could do it this other way" but we never did it those other ways. I'll probably use some of my stipend to buy some equipment -- my budget was due when school ended -- & I'm already looking for grants. People said that ISDs sometimes have equipment to loan out ... but Van Buren doesn't. My friend in the chemistry workshop is having the same problem. So we'll see how well I can adjust things.
4) This was very helpful for a tentative physics teacher; doing it again would be super helpful.
So I've got 20 years of field biology experience. My physics is rusty/ minimal but (once I pass my class this summer) I'll have my DI endorsement & my principal will have me teach physics. Which is fine, I was planning on adding the physics endorsement eventually, I just thought I'd have time to take a few classes & brush up on the content. So this class was great -- physics content & modeling instruction. I'd like to take it again in a few years when I've got the content under control & see what I missed pedagogy-wise. https://fnoschese.wordpress.com/2012/05/30/my-tedxnyed-session-learning-science-by-doing-science/
5) I can see a few ways to apply this to biology already.
To be honest, I've got 4 brand-new preps next year (Science 7C, Science 8A, & Physics A & B) so I won't be making any major changes to biology. I'm hoping that a biology modeling workshop is offered next summer -- I can't work it into my schedule this summer & I really shouldn't try, considering how much I have to get ready before September. This is why I signed up for the biology list-serv. (I wondering if the bio focus will be cellular & smaller or organismal & larger.) http://www.gettingpractical.org.uk/documents/SSRBIologyfieldwork_000.pdf
6) Could this be integrated into teacher preparation programs?
I went thru an alternative program for career-changers, the Woodrow Wilson Teaching Fellowship. We talked a lot about concepts similar to modeling (& a couple of our professors had great talk moves) but we never had a modeling class. Why not? Why isn't one offered in the undergrad program? I'm just starting my 2nd year as a teacher so everything is still new to me, but some of the more experienced teachers were like "This changes everything!" This technique is documented to work -- even with "problem" kids -- so why isn't it more widespread? (The program at Western: http://wmich.edu/teaching/academics/secondary/index.html)
7) This was totally worth the 4 weeks.
& I'm glad our workshop wasn't three 5-day weeks -- I really needed the extra time to process. Even if there wasn't a stipend involved, this was totally worth it. I made connections with local (& not-so-local) teachers, I increased my Twitter presence (altho I might not tweet much now that class is over), & I improved my content & pedagogy both. & luckily, I got to carpool most days so the drive wasn't quite so bad. Sadly, tho, this workshop interfered with my regular summer job at the nature center (http://naturecenter.org/), so I missed out on hearing Wood Thrush singing every day at work. Still worth it, don't get me wrong, but the missing out on the Wood Thrush is a real regret.
Monday, July 13, 2015
Unit 8 -- We're Going in Circles!
We had less than a day for this unit, what with invoices & post-tests & whatnot on the final day. (& we didn't even get to momentum & impulse in Unit 9, so it worked out like it does sometimes in Laura's classroom.) So I'm not going to talk about all the paperwork, that's a bit boring & at all germane to modeling -- I'm just going to talk about the circular motion craziness. :-)
& it did start out crazy -- Don has a flying pig!
So, what forces are acting on a flying pig? & how to draw this? (Let me tell you, this strained my artistic ability. :-) ) After we struggled a bit, Don admitted the wings were a red herring & had us consider a rubber stopper going in a circle on a string instead. In both cases, the speed looked constant, but what about velocity? What about acceleration? What did the schema look like? & then what does the force diagram look like?
Now, I know the centripetal force is towards the center, but drawing out the "shadow forces" of the string really showed why. That's something I'll definitely do with Physical Science in the fall, because this is not anything that makes common sense. If you feel pushed back (or down or whatever), the unbalanced force is in the opposite direction ... which is just weird. If you are going in a circle, there has to be an unbalance force inward.
Don had a story for this unit that he swore was really his own. While travelling cross country, his family stopped at a fair & he & his sister rode the Gravitron. (You stand against a wall, the circular room starts spinning, & then the floor drops away.) So while everyone is plastered to the wall, some guy across from Don unpeels himself from the wall, gets up, & starts walking around. Yikes! Now, this is totally a story I could steal. :-)
To show the "inward force", we all went out into the hall & somebody steered a bowling ball around in a circle with a meter stick. To make the ball turn, you had to push it towards the middle. Boom! Unbalanced force pointing towards the middle! So we added a new move to the velocity dance -- If one hand is pointing to the side, you're turning. (The other physics group used rubber mallets -- They posted a straight-line race a while back.) Somebody gave me a bowling ball years ago, but I eventually gave it to Goodwill. Now I think I need to go get some retired balls from a bowling alley.
We did a few problems from worksheet #1 & drew out the force diagrams. I wanted to make the top of the hill do something cool, but I was wrong. (sigh) The dots on the motion map were referred to as moments of circular motion.
Another good example of the Central Force Theory is spinning a cup of water on a tray. The tray Don used was a little triangular piece of whiteboard while the tray I have is a lunchroom-type tray. I can spin an orange around on mine -- it's got a textured surface & there's a little room to roll -- but Don couldn't spin a ball around on his. Therefore, mine is better -- The kids were real impressed by the orange, & I was too, I honestly didn't think it would work. (& this is when I realized that one of my group mates had been at that same workshop at MSTA last year. How funny is that?)
But when you draw the force diagram for the spinning cup at the top of its arc, the only forces on it are pointing down. How does it stay up? Why doesn't it fall off? Well, it is falling ... only it's falling exactly where the tray is moving to. This kind of ties back into Don's demonstration of "throwing" rubber stoppers to a catcher -- The object is trying to move in a straight line, but the tray is moving around in a circle. If you slow, sure, the cup goes flying, but otherwise the tray intercepts the falling cup perfectly ... & the water hardly wobbles. (I actually like my demo better, with a clear plastic cup half-full of water instead of a red Solo cup filled with a bean bag.)
Then we talked about centrifugal vs centripetal, & it all depends on your frame of reference. Don used the example of a kid holding a ball on the merry-go-round. If you're standing outside the merry-go-round, when the kid lets go of the ball, you can see it move in a straight line. However, if you're the kid, when you let the ball go, you see it move in a curved line, away from you. People specifically mentioned the old "Frames of Reference" video, & I found it! https://www.youtube.com/watch?v=aRDOqiqBUQY
Both Don & Laura say there's no good way to experimentally show this concept, or to show the relationship between the speed of the circular motion & the force & the string length. The best they could come up with was having a bunch of rubber stoppers (of varying masses) on strings & let the kids twirl them around & mess with the string length. They'll get the idea kinesthetically & you can build from there.
We had a reading, an overview of modeling instruction that's perfect for sending to administrators, but we never discussed it. (& yes, I did send it along to my principal.)
& that's it. That's as far as we got. We made a lot of jokes about the end of the semester & cramming stuff in. :-)
Equipment List
Flying Pig or Cow, $10
https://www.giftofwings.com/store1/producti/index2.html
Graph-ruled Composition Book, $3
http://www.officedepot.com/a/products/320155/Office-Depot-Brand-Marble-Quad-Composition/
Bowling Ball (new but on sale), $43
http://www.bowlingball.com/
Rubber Mallet (16 oz), $6.50
http://www.amazon.com/General-2259323-Steelgrip-Rubber-Mallet/dp/B003MRPGDE/ref=pd_sim_469_4?ie=UTF8&refRID=1FD66S3HS35RZVA9KG8A
& it did start out crazy -- Don has a flying pig!
So, what forces are acting on a flying pig? & how to draw this? (Let me tell you, this strained my artistic ability. :-) ) After we struggled a bit, Don admitted the wings were a red herring & had us consider a rubber stopper going in a circle on a string instead. In both cases, the speed looked constant, but what about velocity? What about acceleration? What did the schema look like? & then what does the force diagram look like?
Now, I know the centripetal force is towards the center, but drawing out the "shadow forces" of the string really showed why. That's something I'll definitely do with Physical Science in the fall, because this is not anything that makes common sense. If you feel pushed back (or down or whatever), the unbalanced force is in the opposite direction ... which is just weird. If you are going in a circle, there has to be an unbalance force inward.
Don had a story for this unit that he swore was really his own. While travelling cross country, his family stopped at a fair & he & his sister rode the Gravitron. (You stand against a wall, the circular room starts spinning, & then the floor drops away.) So while everyone is plastered to the wall, some guy across from Don unpeels himself from the wall, gets up, & starts walking around. Yikes! Now, this is totally a story I could steal. :-)
To show the "inward force", we all went out into the hall & somebody steered a bowling ball around in a circle with a meter stick. To make the ball turn, you had to push it towards the middle. Boom! Unbalanced force pointing towards the middle! So we added a new move to the velocity dance -- If one hand is pointing to the side, you're turning. (The other physics group used rubber mallets -- They posted a straight-line race a while back.) Somebody gave me a bowling ball years ago, but I eventually gave it to Goodwill. Now I think I need to go get some retired balls from a bowling alley.
We did a few problems from worksheet #1 & drew out the force diagrams. I wanted to make the top of the hill do something cool, but I was wrong. (sigh) The dots on the motion map were referred to as moments of circular motion.
Another good example of the Central Force Theory is spinning a cup of water on a tray. The tray Don used was a little triangular piece of whiteboard while the tray I have is a lunchroom-type tray. I can spin an orange around on mine -- it's got a textured surface & there's a little room to roll -- but Don couldn't spin a ball around on his. Therefore, mine is better -- The kids were real impressed by the orange, & I was too, I honestly didn't think it would work. (& this is when I realized that one of my group mates had been at that same workshop at MSTA last year. How funny is that?)
But when you draw the force diagram for the spinning cup at the top of its arc, the only forces on it are pointing down. How does it stay up? Why doesn't it fall off? Well, it is falling ... only it's falling exactly where the tray is moving to. This kind of ties back into Don's demonstration of "throwing" rubber stoppers to a catcher -- The object is trying to move in a straight line, but the tray is moving around in a circle. If you slow, sure, the cup goes flying, but otherwise the tray intercepts the falling cup perfectly ... & the water hardly wobbles. (I actually like my demo better, with a clear plastic cup half-full of water instead of a red Solo cup filled with a bean bag.)
Then we talked about centrifugal vs centripetal, & it all depends on your frame of reference. Don used the example of a kid holding a ball on the merry-go-round. If you're standing outside the merry-go-round, when the kid lets go of the ball, you can see it move in a straight line. However, if you're the kid, when you let the ball go, you see it move in a curved line, away from you. People specifically mentioned the old "Frames of Reference" video, & I found it! https://www.youtube.com/watch?v=aRDOqiqBUQY
Both Don & Laura say there's no good way to experimentally show this concept, or to show the relationship between the speed of the circular motion & the force & the string length. The best they could come up with was having a bunch of rubber stoppers (of varying masses) on strings & let the kids twirl them around & mess with the string length. They'll get the idea kinesthetically & you can build from there.
We had a reading, an overview of modeling instruction that's perfect for sending to administrators, but we never discussed it. (& yes, I did send it along to my principal.)
& that's it. That's as far as we got. We made a lot of jokes about the end of the semester & cramming stuff in. :-)
Equipment List
Flying Pig or Cow, $10
https://www.giftofwings.com/store1/producti/index2.html
Graph-ruled Composition Book, $3
http://www.officedepot.com/a/products/320155/Office-Depot-Brand-Marble-Quad-Composition/
Bowling Ball (new but on sale), $43
http://www.bowlingball.com/
Rubber Mallet (16 oz), $6.50
http://www.amazon.com/General-2259323-Steelgrip-Rubber-Mallet/dp/B003MRPGDE/ref=pd_sim_469_4?ie=UTF8&refRID=1FD66S3HS35RZVA9KG8A
Unit 7 - Energy!
This is another idea-heavy unit that doesn't start out with a paradigm lab. So instead Don started us out with a demo he does on parent night. He had a variety of balls & he asked what would happen if he bounced them off the floor & to the underside of the table. & to make it easy, he gave us multiple choice: A) The ball goes floor-Don. B) The ball goes floor-table-floor-table-floor-floor-floor. (Bonus points if you can name a Dr Seuss book that goes with this!) C) The ball goes floor-Adam (who was in the catcher's position). The thing is, different balls behaved differently, & of course he didn't offer any explanation. :-)
So, we started out listing all the possible answers to "What is energy?" -- heat, electric, ATP, the ability to do work, etc. Then we moved into "What is work?" -- landscaping, using force to move something, power, etc. Then Laura wrote out the 1st Rule of Energy: All energy is stored. It must be stored some place and we can "see" something about it. (The "see" is in quotes because sometimes it's microscopic or smaller, beyond our ability to see with our eyes.) For the energy list, we went back thru & wrote down where the energy was stored -- electric in the movement of electrons, solar in the sun & the particles, be they waves or photons, etc -- & separated out the ones that sounded like definitions -- the ability to do work & ability to move. (We didn't do this for work. Would we have come back to it if we had time? This was near the end of the workshop & I know we skipped some things for time's sake.) The things like "heat" & "potential", we put question marks by for later.
Then Laura came up with the Big Questions: Where is energy stored? Where does it come from? Where does it go? (Cotton-eyed Joe...) What does it do? These are the questions we answered in various ways the rest of the unit. (However, a question I am left with is why didn't I get a picture of this board?)
We talked a lot about how energy is only an idea. There's no energy-ometer, you can't really see it. We used 2 specific analogies: Energy is like money & energy is like information. You can store money/ information in lots of ways, you can transfer money/ information in lots of way, they both flow around, but really, they're not real -- They're just ideas. (Yes, even money is just an idea. Really.)
So we first represented the energy in a tumble buggy using a pie chart. We were careful to define what was in the system: buggy, battery, & surroundings. Then we drew the energy pie at 3 different instances: before the buggy is switched on, at the 2-second mark, at the 2-minute mark, & stopped after 2 minutes. These were just qualitative pie charts, the proportions we thought made sense, no numbers involved yet.
& of course we discussed where the energy was stored, where it went, & what it did. I want to get one of those thermal imagers so I can show kids the ghostly "heat footprints" left behind when they walk across the floor. Anyways. We shortened energy stored in the battery's chemical bonds as Echem. (Yet again, sorry there's not subscript capability.) The energy of motion, or kinetic energy, we shortened to Ek. The energy lost to the surroundings we shortened to Elostsurr or Esurr or Elost. (Apparently they used to say dissipated energy that thanks to all the Viagra commercials, Ed now has a different meaning.) Elost is a bit thorny, tho -- Some kids will be literal & think the energy is just gone & lost forever, not simply transferred out of the system to, say, the air molecules as sound/ light or to the carpet fibers as crushing/ heat.
We also drew the same 4 pie charts but only considering the buggy as the system. The pies were much smaller & when it was turned off, there were no pies. (Some groups used dots to show this but we had pies labeled "empty". We figured that a dot would mean something was there & since we didn't change the chemical energy in the plastic, etc we didn't want to show those.)
So then we watched the PhET demo of the energy skate park (which I used last year in Physical Science; https://phet.colorado.edu/en/simulation/energy-skate-park) because that uses pie charts too. (I was glad to hear I wasn't the only one who had trouble with the PhET simulations. My classroom uses Chromebooks & only the HTML5 versions of the simulations work ... & not all simulations have that option. It's annoying because they all work on my home computer -- & my school computer! -- so if I'm not paying attention, I'll choose things my students can't access. Hmph. Anyways.
Don introduced a track with a rubber band strung up at one end & asked us to draw the energy diagram just before release & at a point further down the track. We shortened the energy of the elastic stretch to Eel or (my favorite) Eboing. Then the track was placed on a slant. At the second point, where the cart stops & starts back down, I called that "Sarah's energy", because it went down the hill. But actually we called that gravitational energy (not energy of position, that's too vague) or Eg. & Don did a demo with a popper dropper -- Does the distance it bounces back up change depending what height you drop it from? (& no, it doesn't. They always bounced up to about eye height. Well, eye height on Don.) The energy for the bounce is stored in the shape, not in the falling/ kinetic energy. That'll be fun to do with my kids.
At this point we stopped, did worksheet #1, & practiced facilitating discussions. I'm pretty sure when we get back together in October, what we'll mostly talk about is whiteboarding & discussions. My physics class doesn't start until 2nd tri, so after Thanksgiving, but luckily I'll have Physical Science in the fall. Really, facilitating discussions needs practice, yes, but it'll be so much easier when I'm the person who designed the lesson so I know exactly what I want to the students to discover.
Lab time! We investigated the distance of the stretch length & the pull force -- Each group had a different spring & each group got a different slope. That slope is the spring "konstant", which means we found Hooke's Law: F=kx. But then we looked for energy on the graph -- It wasn't either axis or the line itself (or the slope), it was the area between the line & the horizontal axis. So with a bit of algebraic substitution, we came up with E=(1/2)kx^2.
We also talked about the fundamental units -- meters, kilograms, & seconds -- & derived units -- newtons & joules. A newton is really kg-m/s/s & a joule is really N-m. We also had an aside about Newton & Hooke & their ideas about gravity. I hadn't realized Newton was such a jerk! Which means, of course, now I need to find anecdotes about 180 scientists, one for every school day. :-/
Before we moved on to energy bar graphs, Don did a demo about the different ways we can see energy. He smashed 2 large steelies together & singed a hole in a piece of paper. Does kinetic energy get transformed into heat energy? You bet! It even works with 1" steelies, just not as well.
So, worksheet #3a had LOL charts to fill out. The first L was the initial energy bar graph, the O was the energy flow diagram (what's in the system & what's not), & the last L was the final energy bar graph. Before Don set us loose on this worksheet, he told us a story about Richard Feynman giving 4 blocks to his nephew, & even when the kid lost the blocks, there were still 4 blocks (you just had to find them). So these graphs aren't quantified either, we only used 4 blocks. (This is totally a story I can steal -- I've got nephews...) The tricky part was, if energy was lost to the surroundings -- not one of the 3 choices on the pre-made graph -- we had to draw those blocks with an arrow out in the surroundings. If it's not in the system, it's not on the bar graph.
& then we had our final labs. We investigated the relationship between the energy of the rubber band & the velocity of the cart, between the energy of the rubber band & the vertical height the cart obtained (on a tilted track, obviously), & between the energy of the rubber band & the slide distance (using a friction block). They were trying to stuff things in for our penultimate day -- Normally, for kids, these labs would each be a day or 2.
So, for energy & velocity... Plotting our data on both Excel & Logger Pro, the formulas came up different. Excel: y=1.44x^0.62 & Logger Pro: y=1.35x^0.55. All of the data were the same, so why the difference? Don wrote the equation out as v = __ E^2, did some algebraic rearrangement, & came up with Ek = (1/coefficient^2) v^2, & asked to google "kinetic energy velocity" -- The official formula is Ek = (1/2) m v^2.
For energy & height, during the lab discussion, we drew the 4-block LOL charts. The elastic energy of the rubber band entirely transfers over to the gravitational field energy of the cart of the top of its trip (assuming no friction, of course). We also know that the force of the gravitational field on the cart is F=mg, the mass of the cart times the field strength. My notes are not as clear here but we went from h=__Espring to h=__Egrav to Egrav = h/ coefficient to Egrav = mgh. I'm pretty sure we didn't do a lot of math there, it was using the force (which is mg) vs distance (or h) graph -- Energy is the area between the line & the axis. & google totally verified this.
The discussion of our final lab results had more algebra & less googling. We drew out the LOL charts & showed that all the energy went to the surroundings (thanks, friction!). So we said friction equaled mu times the perpendicular force (or mg). Then we went from d=__Eel to d=__Esurr to Esurr = (1/coefficient) d. We made a force vs distance graph & found the area & came up with Esurr=fd (energy lost to surroundings equals frictional force times distance). Another way to say that is Esurr = (mu) m g d, the work done by friction. We defined work as energy transferred by force with very little discussion & the day was over & we all went home.
We only had 1 reading for this unit, "Making Work Work" (which is the best title ever). Even tho this article was only 12 pages long, it was a harder read than the 44 pages of the 5 Practices book the night before. (sigh) But the whole article boiled down to "work is a technical term & we're misusing it both in speaking & in equations". I really liked his gravitational field & gravitational energy example & the curvature of space-time ... but I needed a graphic for that, not just words. One of my group members suggested How to Teach Relativity to Your Dog (http://www.amazon.com/How-Teach-Relativity-Your-Dog/dp/0465023312), so I have that on order. :-)
Here's another "summation" thing we discussed: When you analyze a graph, what do you look for? 1) slope 2) equation 3) trends in the data 4) values of the data 5) area
Equipment List
Dropper Popper, $3
http://www.teachersource.com/product/dropper-popper/energy
C-Clamps (3 sizes), $11
http://www.amazon.com/TEKTON-91809-Heavy-Duty-C-Clamp-3-Piece/dp/B00BRL59HK/ref=lp_553158_1_3?s=power-hand-tools&ie=UTF8&qid=1436852033&sr=1-3
Big Rubber Bands (24 pack), $3.50
http://www.staples.ca/en/Staples-Economy-Big-Rubber-Bands-Size-117B/product_383318_2-CA_1_20001
Shower Board (4 ft x 8 ft), $13.50
http://www.lowes.com/pd_16605-46498-300_0__?productId=3015239
Expo Markers, assorted colors (12 pack), $16.50
http://www.amazon.com/Expo-Low-Odor-Markers-Chisel-12-Pack/dp/B00006JNK2
Pasco Friction Block, $22
http://www.pasco.com/prodCatalog/ME/ME-9807_friction-block-ids/
Assorted Springs (200), $5
http://www.harborfreight.com/200-piece-assorted-spring-set-67562.html
So, we started out listing all the possible answers to "What is energy?" -- heat, electric, ATP, the ability to do work, etc. Then we moved into "What is work?" -- landscaping, using force to move something, power, etc. Then Laura wrote out the 1st Rule of Energy: All energy is stored. It must be stored some place and we can "see" something about it. (The "see" is in quotes because sometimes it's microscopic or smaller, beyond our ability to see with our eyes.) For the energy list, we went back thru & wrote down where the energy was stored -- electric in the movement of electrons, solar in the sun & the particles, be they waves or photons, etc -- & separated out the ones that sounded like definitions -- the ability to do work & ability to move. (We didn't do this for work. Would we have come back to it if we had time? This was near the end of the workshop & I know we skipped some things for time's sake.) The things like "heat" & "potential", we put question marks by for later.
Then Laura came up with the Big Questions: Where is energy stored? Where does it come from? Where does it go? (Cotton-eyed Joe...) What does it do? These are the questions we answered in various ways the rest of the unit. (However, a question I am left with is why didn't I get a picture of this board?)
We talked a lot about how energy is only an idea. There's no energy-ometer, you can't really see it. We used 2 specific analogies: Energy is like money & energy is like information. You can store money/ information in lots of ways, you can transfer money/ information in lots of way, they both flow around, but really, they're not real -- They're just ideas. (Yes, even money is just an idea. Really.)
So we first represented the energy in a tumble buggy using a pie chart. We were careful to define what was in the system: buggy, battery, & surroundings. Then we drew the energy pie at 3 different instances: before the buggy is switched on, at the 2-second mark, at the 2-minute mark, & stopped after 2 minutes. These were just qualitative pie charts, the proportions we thought made sense, no numbers involved yet.
& of course we discussed where the energy was stored, where it went, & what it did. I want to get one of those thermal imagers so I can show kids the ghostly "heat footprints" left behind when they walk across the floor. Anyways. We shortened energy stored in the battery's chemical bonds as Echem. (Yet again, sorry there's not subscript capability.) The energy of motion, or kinetic energy, we shortened to Ek. The energy lost to the surroundings we shortened to Elostsurr or Esurr or Elost. (Apparently they used to say dissipated energy that thanks to all the Viagra commercials, Ed now has a different meaning.) Elost is a bit thorny, tho -- Some kids will be literal & think the energy is just gone & lost forever, not simply transferred out of the system to, say, the air molecules as sound/ light or to the carpet fibers as crushing/ heat.
We also drew the same 4 pie charts but only considering the buggy as the system. The pies were much smaller & when it was turned off, there were no pies. (Some groups used dots to show this but we had pies labeled "empty". We figured that a dot would mean something was there & since we didn't change the chemical energy in the plastic, etc we didn't want to show those.)
So then we watched the PhET demo of the energy skate park (which I used last year in Physical Science; https://phet.colorado.edu/en/simulation/energy-skate-park) because that uses pie charts too. (I was glad to hear I wasn't the only one who had trouble with the PhET simulations. My classroom uses Chromebooks & only the HTML5 versions of the simulations work ... & not all simulations have that option. It's annoying because they all work on my home computer -- & my school computer! -- so if I'm not paying attention, I'll choose things my students can't access. Hmph. Anyways.
Don introduced a track with a rubber band strung up at one end & asked us to draw the energy diagram just before release & at a point further down the track. We shortened the energy of the elastic stretch to Eel or (my favorite) Eboing. Then the track was placed on a slant. At the second point, where the cart stops & starts back down, I called that "Sarah's energy", because it went down the hill. But actually we called that gravitational energy (not energy of position, that's too vague) or Eg. & Don did a demo with a popper dropper -- Does the distance it bounces back up change depending what height you drop it from? (& no, it doesn't. They always bounced up to about eye height. Well, eye height on Don.) The energy for the bounce is stored in the shape, not in the falling/ kinetic energy. That'll be fun to do with my kids.
At this point we stopped, did worksheet #1, & practiced facilitating discussions. I'm pretty sure when we get back together in October, what we'll mostly talk about is whiteboarding & discussions. My physics class doesn't start until 2nd tri, so after Thanksgiving, but luckily I'll have Physical Science in the fall. Really, facilitating discussions needs practice, yes, but it'll be so much easier when I'm the person who designed the lesson so I know exactly what I want to the students to discover.
Lab time! We investigated the distance of the stretch length & the pull force -- Each group had a different spring & each group got a different slope. That slope is the spring "konstant", which means we found Hooke's Law: F=kx. But then we looked for energy on the graph -- It wasn't either axis or the line itself (or the slope), it was the area between the line & the horizontal axis. So with a bit of algebraic substitution, we came up with E=(1/2)kx^2.
We also talked about the fundamental units -- meters, kilograms, & seconds -- & derived units -- newtons & joules. A newton is really kg-m/s/s & a joule is really N-m. We also had an aside about Newton & Hooke & their ideas about gravity. I hadn't realized Newton was such a jerk! Which means, of course, now I need to find anecdotes about 180 scientists, one for every school day. :-/
Before we moved on to energy bar graphs, Don did a demo about the different ways we can see energy. He smashed 2 large steelies together & singed a hole in a piece of paper. Does kinetic energy get transformed into heat energy? You bet! It even works with 1" steelies, just not as well.
So, worksheet #3a had LOL charts to fill out. The first L was the initial energy bar graph, the O was the energy flow diagram (what's in the system & what's not), & the last L was the final energy bar graph. Before Don set us loose on this worksheet, he told us a story about Richard Feynman giving 4 blocks to his nephew, & even when the kid lost the blocks, there were still 4 blocks (you just had to find them). So these graphs aren't quantified either, we only used 4 blocks. (This is totally a story I can steal -- I've got nephews...) The tricky part was, if energy was lost to the surroundings -- not one of the 3 choices on the pre-made graph -- we had to draw those blocks with an arrow out in the surroundings. If it's not in the system, it's not on the bar graph.
& then we had our final labs. We investigated the relationship between the energy of the rubber band & the velocity of the cart, between the energy of the rubber band & the vertical height the cart obtained (on a tilted track, obviously), & between the energy of the rubber band & the slide distance (using a friction block). They were trying to stuff things in for our penultimate day -- Normally, for kids, these labs would each be a day or 2.
So, for energy & velocity... Plotting our data on both Excel & Logger Pro, the formulas came up different. Excel: y=1.44x^0.62 & Logger Pro: y=1.35x^0.55. All of the data were the same, so why the difference? Don wrote the equation out as v = __ E^2, did some algebraic rearrangement, & came up with Ek = (1/coefficient^2) v^2, & asked to google "kinetic energy velocity" -- The official formula is Ek = (1/2) m v^2.
For energy & height, during the lab discussion, we drew the 4-block LOL charts. The elastic energy of the rubber band entirely transfers over to the gravitational field energy of the cart of the top of its trip (assuming no friction, of course). We also know that the force of the gravitational field on the cart is F=mg, the mass of the cart times the field strength. My notes are not as clear here but we went from h=__Espring to h=__Egrav to Egrav = h/ coefficient to Egrav = mgh. I'm pretty sure we didn't do a lot of math there, it was using the force (which is mg) vs distance (or h) graph -- Energy is the area between the line & the axis. & google totally verified this.
The discussion of our final lab results had more algebra & less googling. We drew out the LOL charts & showed that all the energy went to the surroundings (thanks, friction!). So we said friction equaled mu times the perpendicular force (or mg). Then we went from d=__Eel to d=__Esurr to Esurr = (1/coefficient) d. We made a force vs distance graph & found the area & came up with Esurr=fd (energy lost to surroundings equals frictional force times distance). Another way to say that is Esurr = (mu) m g d, the work done by friction. We defined work as energy transferred by force with very little discussion & the day was over & we all went home.
We only had 1 reading for this unit, "Making Work Work" (which is the best title ever). Even tho this article was only 12 pages long, it was a harder read than the 44 pages of the 5 Practices book the night before. (sigh) But the whole article boiled down to "work is a technical term & we're misusing it both in speaking & in equations". I really liked his gravitational field & gravitational energy example & the curvature of space-time ... but I needed a graphic for that, not just words. One of my group members suggested How to Teach Relativity to Your Dog (http://www.amazon.com/How-Teach-Relativity-Your-Dog/dp/0465023312), so I have that on order. :-)
Here's another "summation" thing we discussed: When you analyze a graph, what do you look for? 1) slope 2) equation 3) trends in the data 4) values of the data 5) area
Equipment List
Dropper Popper, $3
http://www.teachersource.com/product/dropper-popper/energy
C-Clamps (3 sizes), $11
http://www.amazon.com/TEKTON-91809-Heavy-Duty-C-Clamp-3-Piece/dp/B00BRL59HK/ref=lp_553158_1_3?s=power-hand-tools&ie=UTF8&qid=1436852033&sr=1-3
Big Rubber Bands (24 pack), $3.50
http://www.staples.ca/en/Staples-Economy-Big-Rubber-Bands-Size-117B/product_383318_2-CA_1_20001
Shower Board (4 ft x 8 ft), $13.50
http://www.lowes.com/pd_16605-46498-300_0__?productId=3015239
Expo Markers, assorted colors (12 pack), $16.50
http://www.amazon.com/Expo-Low-Odor-Markers-Chisel-12-Pack/dp/B00006JNK2
Pasco Friction Block, $22
http://www.pasco.com/prodCatalog/ME/ME-9807_friction-block-ids/
Assorted Springs (200), $5
http://www.harborfreight.com/200-piece-assorted-spring-set-67562.html
Unit 6 -- Projectile Motion! (It's like patting your head & rubbing your tummy, while falling thru the air)
This unit took just over a day to cover. Zoom! It started with a teaser -- Don had his standard stick figure dropping a ball off a tall building & asked how far the ball travels at every second. We created a T-chart showing the distance for 0 to 4 seconds, then compared those numbers (from using the delta-y = (1/2) a t^2 formula) to the results of shading in the area "under the curve" -- Go figure, exactly the same! :-) & the distance traveled increases by another 10 meters each second, so thank you free fall acceleration. The he drew 2 stick figures -- one just standing & one on a skateboard -- & asked which would hit the ground first. & then it was time to go for the night. O the suspense!
So when we got back, we actually had a "side demo" first. He talked a bit about air resistance, then dropped coffee filters & asked which would hit first, the single one or the double one. (It was the double.) Could we figure out this relationship? This is the process of science! 1) Ask a question. 2) Collect data. 3) Organize & analyze data. 4) Draw conclusion. 5) Make a mental model -- with predictive power! 6) Use the model, & adjust when needed. So that's a nice little wrap up, before the workshop is over.
But then we got back to those poor stick people jumping (or skateboarding) off the building. Don did a demo in the hallway (that'll take me a long time to get right) where he dropped one golf ball straight down & threw the other out to the side. We listened & heard them hit at the same time, even when he barely gave the sideways ball any oomph. Then he asked what happens if you angle the sideways ball up (it hits later) or down (it hits earlier). You could do this demo with ping pong balls if you were worried about breaking stuff -- It'll just take practice. So that's a great demo of what would happen to the stick people & a good way to introduce the dissociation of sideways movement from downways movement.
Then he had us watch a video of a ball being thrown across the screen (http://gpschools.schoolwires.net/Page/1780, at the very top). He had a volunteer put a sticky note at every location of the ball when it was slowed down to single frames. Who's our friend? Symmetry! & the horizontal spacing looked pretty equal so the sideways velocity had to be constant. What shape is it? A parabola! All projectiles fly in parabolas (except that my notes say "all projectiles fly in projectiles", sheesh). So we wrote out that the horizontal motion had constant velocity & the appropriate formula & that the vertical motion has constant acceleration (free fall, remember?) & the formula for that, & then we were set loose on worksheet #1. (This was the math-iest thing we've done so far.)
Also, Perfect Pic is an app that will slow down any video to 20 frames per second -- I'm not sure if this is what Don't video used but a person in my next group had it for her iPad & it was pretty useful. We'll see if it's available for Android devices (& if it's free). I can't find it right now so I might have to do more digging...
Then we had to draw a motion map by second & to scale of somebody dropping a ball from 40 meters off the ground. The key here is that the velocity & acceleration arrows don't have to be proportional to the distances.
Then we worked on worksheet #2 for a while & then we moved directly into the challenge -- trying to bounce a steelie off of a cup on the floor. We had to use a ramp down to the track. My groupmates did most of the work & they didn't put it on a whiteboard. (They were really into the challenge.)
We had a second challenge, where people could choose either group -- either shoot a ball so that it knocked a cup over on a table (at the same height it was launched from) or shoot a ball & knock over a cup on the floor. I wouldn't use those launchers anywhere near glass but they were fun. I was in the symmetrical group & we got close but no cigar.
We did have a reading for this unit -- 5 Practices for Orchestrating Productive Task-based Discussions in Science (http://www.nsta.org/store/product_detail.aspx?id=10.2505/9780873537452). (The math version, http://www.amazon.com/Practices-Orchestrating-Productive-Mathematics-Discussions/dp/0873536770, came first. I'm going to recommend my Woodrow Wilson advisor get these books as appropriate for next year's monthly seminars, since we're all math & science.) The first 2 chapters of this book really stressed that good discussions depend on the teacher's preparation -- choosing good things to discussion, moving the discussion along (with the talk moves), having questions prepared, & especially knowing where the lesson is going. A wandering discussion doesn't teach anyone anything, except that you can get off-track & never recover.
Our homework for our readings is to tweet about them. This proved to be somewhat dangerous, as Don retweeted what somebody said (it was about students showing what they know via whiteboards & the teacher being prepared with linking ideas & probing questions) & then a random modeler took issue with the statement, saying the students should ask the questions & link ideas. Well yes, that's the whole goal of modeling, but you have to be prepared to invisibly lead the discussions to where they need to go. This outside person didn't realize the original post was from a student in regards to a reading assignment. Anyways, the whole situation got a bit weird. Needless to say, "I strongly disagree" & "Mind your own business" have entered our group's in-jokes. :-)
Don also talked about stands-based grading some more (& in fact did a lunchtime Prezi on it a few days later). Here are the standards he uses for his Physics classes: http://gpschools.schoolwires.net/Page/12329 You'll note these aren't the state standards or the Next Gen standards -- Instead, he's combined them & condensed them down. (& in fact he's got performance standards too, like drop an egg off the building without breaking it, which aren't listed.) Students can see what exactly they need to work on instead of just "study harder". So I might try this in Physics next year, with a class of 15 rather than 25 or 30 (which I figure my other classes will be). The Physics kids are more likely to be willing to take a risk & the messing about with grades will be easier (Don averages stuff out with Excel first before he puts it in whatever online grade book). But I better see if my principal is on board with that first...
Equipment List
Shoot the Monkey Demonstration Kit, $68
http://www.flinnsci.com/store/Scripts/prodView.asp?idproduct=16289&noList=1
Long-range Projectile Launcher, $389
http://www.pasco.com/prodCatalog/ME/ME-6801_projectile-launcher-long-range/
So when we got back, we actually had a "side demo" first. He talked a bit about air resistance, then dropped coffee filters & asked which would hit first, the single one or the double one. (It was the double.) Could we figure out this relationship? This is the process of science! 1) Ask a question. 2) Collect data. 3) Organize & analyze data. 4) Draw conclusion. 5) Make a mental model -- with predictive power! 6) Use the model, & adjust when needed. So that's a nice little wrap up, before the workshop is over.
But then we got back to those poor stick people jumping (or skateboarding) off the building. Don did a demo in the hallway (that'll take me a long time to get right) where he dropped one golf ball straight down & threw the other out to the side. We listened & heard them hit at the same time, even when he barely gave the sideways ball any oomph. Then he asked what happens if you angle the sideways ball up (it hits later) or down (it hits earlier). You could do this demo with ping pong balls if you were worried about breaking stuff -- It'll just take practice. So that's a great demo of what would happen to the stick people & a good way to introduce the dissociation of sideways movement from downways movement.
Then he had us watch a video of a ball being thrown across the screen (http://gpschools.schoolwires.net/Page/1780, at the very top). He had a volunteer put a sticky note at every location of the ball when it was slowed down to single frames. Who's our friend? Symmetry! & the horizontal spacing looked pretty equal so the sideways velocity had to be constant. What shape is it? A parabola! All projectiles fly in parabolas (except that my notes say "all projectiles fly in projectiles", sheesh). So we wrote out that the horizontal motion had constant velocity & the appropriate formula & that the vertical motion has constant acceleration (free fall, remember?) & the formula for that, & then we were set loose on worksheet #1. (This was the math-iest thing we've done so far.)
Also, Perfect Pic is an app that will slow down any video to 20 frames per second -- I'm not sure if this is what Don't video used but a person in my next group had it for her iPad & it was pretty useful. We'll see if it's available for Android devices (& if it's free). I can't find it right now so I might have to do more digging...
Then we had to draw a motion map by second & to scale of somebody dropping a ball from 40 meters off the ground. The key here is that the velocity & acceleration arrows don't have to be proportional to the distances.
Then we worked on worksheet #2 for a while & then we moved directly into the challenge -- trying to bounce a steelie off of a cup on the floor. We had to use a ramp down to the track. My groupmates did most of the work & they didn't put it on a whiteboard. (They were really into the challenge.)
We had a second challenge, where people could choose either group -- either shoot a ball so that it knocked a cup over on a table (at the same height it was launched from) or shoot a ball & knock over a cup on the floor. I wouldn't use those launchers anywhere near glass but they were fun. I was in the symmetrical group & we got close but no cigar.
We did have a reading for this unit -- 5 Practices for Orchestrating Productive Task-based Discussions in Science (http://www.nsta.org/store/product_detail.aspx?id=10.2505/9780873537452). (The math version, http://www.amazon.com/Practices-Orchestrating-Productive-Mathematics-Discussions/dp/0873536770, came first. I'm going to recommend my Woodrow Wilson advisor get these books as appropriate for next year's monthly seminars, since we're all math & science.) The first 2 chapters of this book really stressed that good discussions depend on the teacher's preparation -- choosing good things to discussion, moving the discussion along (with the talk moves), having questions prepared, & especially knowing where the lesson is going. A wandering discussion doesn't teach anyone anything, except that you can get off-track & never recover.
Our homework for our readings is to tweet about them. This proved to be somewhat dangerous, as Don retweeted what somebody said (it was about students showing what they know via whiteboards & the teacher being prepared with linking ideas & probing questions) & then a random modeler took issue with the statement, saying the students should ask the questions & link ideas. Well yes, that's the whole goal of modeling, but you have to be prepared to invisibly lead the discussions to where they need to go. This outside person didn't realize the original post was from a student in regards to a reading assignment. Anyways, the whole situation got a bit weird. Needless to say, "I strongly disagree" & "Mind your own business" have entered our group's in-jokes. :-)
Don also talked about stands-based grading some more (& in fact did a lunchtime Prezi on it a few days later). Here are the standards he uses for his Physics classes: http://gpschools.schoolwires.net/Page/12329 You'll note these aren't the state standards or the Next Gen standards -- Instead, he's combined them & condensed them down. (& in fact he's got performance standards too, like drop an egg off the building without breaking it, which aren't listed.) Students can see what exactly they need to work on instead of just "study harder". So I might try this in Physics next year, with a class of 15 rather than 25 or 30 (which I figure my other classes will be). The Physics kids are more likely to be willing to take a risk & the messing about with grades will be easier (Don averages stuff out with Excel first before he puts it in whatever online grade book). But I better see if my principal is on board with that first...
Equipment List
Shoot the Monkey Demonstration Kit, $68
http://www.flinnsci.com/store/Scripts/prodView.asp?idproduct=16289&noList=1
Long-range Projectile Launcher, $389
http://www.pasco.com/prodCatalog/ME/ME-6801_projectile-launcher-long-range/
Unit 5 -- Unbalanced Forces? Acceleration Again!
For this unit, we had 2 readings: the Talk Science Primer (discussed in Unit 4) & chapter 3 of Arons. This chapter was all about elementary dynamics & he circled back around to vocabulary & learning thru discussion. Force, mass, & gravity all have technical meanings -- & gravity is just the name, not the effect! -- that most people are not aware of. He shows a way to derive F=ma from experimentation, which is not how we did it in class. This chapter also covers inertia & force pairs, so Newton's other 2 laws, & is pretty keen on multiple force diagrams & descriptions written alongside them. He also goes off on the different uses for "=", which gave me flashbacks to discussions in my math practices class. It's pretty clear he's writing for other PhDs, for professors teaching physics to undergraduates -- He used "gedanken" experiment & didn't define it, when "thought experiment" would have worked just as well. So I guess I'm not surprised that the demonstrations he suggests aren't illustrated, for the most part. (When I tweeted that I needed a coin & feather vacuum tube -- I've shown this bowling ball & feathers video, linked in Unit 4, but it'd be nice to do it in class -- & was followed by a vacuum tube manufacturer. Huh?) Luckily, there's a video for the flea pulling 50 pounds of dry ice: https://www.youtube.com/watch?v=5LcnnEwaXy0
The 2 videos we watched were both about growth mindset. (There are bunches & I can't find the exact ones we saw.) This is Carol Dweck's idea & it's all about praising the effort, not the intelligence. In fact, when you praise a kid for being smart, you set them up for failure -- When they struggle, they feel dumb; when they struggle, they give up; when they struggle, they go back to the easier situation where they were "smart". When you praise the effort, they try harder things. So this is a book (http://www.amazon.com/Mindset-The-New-Psychology-Success/dp/0345472322) that I'll need to read, hopefully before the summer's over.
But the "student mode" unit started with us trying to apply constant force to the hover car. By the end of the 3rd table, we were running!
Then we had a pair of experiments -- what's the relationship between force & acceleration & what's the relationship between mass & acceleration? (We talked about ramp angle but decided that would be confounding so we kept the tracks flat.) So we set up our track with a motion sensor & had one person push the cart along with a spring scale, increasing the force each time. We ended up with a = 0.91F. Next we had that same person push the cart along, increasing the mass each time. We ended up with a = 0.56 (1/m).
Don led a discussion (he was at the front board) where we linked up the formulas from these 2 experiments. He combined the 2 equations into a = __F/m & we plugged data in from our experiments to figure out the missing coefficient. (Our group came up with 0.8 & 0.86, using a 1 kg cart being pushed at 1 N & 1.5 N.) Then he listed the coefficients the groups came up with, which ranged from 0.85 to 1.4. Since nature doesn't use random numbers (& since all the pushers had noted how hard it was to push with a constant force, even for less than 2 meters), we went with a coefficient of 1, which means we came up with this final equation: a = F/m. (It's important to note here that F is the unbalanced force, or Funbal. Curse this blog program for not doing subscripts!) This is Newton's 2nd law, written out with the causes of change on one side & what gets changed on the other. This made a lot more sense to me than how Arons showed it in his chapter.
Pushing with the spring scales reinforces the concept of what a force is -- a push or pull. I really need to get some push-&-pull spring scales. Again, it's a shame that I had to turn in my budget at the end of the school year -- There's definitely stuff I would swap out now. (Altho I am pretty excited about dissecting hearts next year.)
We also discussed units, because they get messy here. Acceleration is measured in m/s/s, force is measured in N, & mass is measured in kg. So a kilogram is a measurement of an object's resistance to motion & a newton is a measurement of the force required to accelerate a 1-kg object to 1 m/s/s. (Don threw in "sticks, bricks, & clicks" as an alternative measuring system, just to rub it in how arbitrary measurements are. I need to find a good history of the metric system...) We were advised to not make a big deal about it, unless students asked. So we'll see how that goes. :-)
To help solidify our understanding, Don drew a picture of 2 people pulling on a skateboarder, one with 100 N of force & the other with 120 N of force. Which way does the skateboarder go? In the direction of the unbalanced force. & then he had us imagine the forces in an elevator & where they were balanced vs unbalanced (& how we felt). The most important thing here is that we don't feel the force of the entire earth pulling us down, only the force of the floor pushing us up. (That's an interesting biology fact.) & then we did worksheet #1.
From this point on, for every worksheet, we divided up into 2 smaller groups & practiced leading discussions. We used the list of talk moves from the Talk Science Primer & the bookmarks from Laura. This apparently is what people say is the biggest lack -- not enough practice leading discussions. (Which is probably why the chem group started leading discussions pretty early on, at least if I'm interpreting their tweets correctly.) So this was good practice -- most people questioned the people who worked on the problem great but didn't necessarily include the rest of the group, which is pretty standard teaching-as-is-done-currently -- but it also ended up being an interesting sociological observation. When the facilitator called on people to lead the discussion, who did they pick & why? When people just volunteered, who was it & why? The class was 50-50 male-to-female but it was mostly the guys who volunteered (or were called on, depending). Were the guys more experienced physics teachers & so more willing to take risks & practice facilitating? Were the guys just more willing to take risks regardless? Did facilitators call on people they spent "after school" time with? So, maybe not what I was supposed to learn but I did get to observe & practice my talk moves too. Here's a link to a math version of the talk moves: http://www.scholastic.com/teachers/top-teaching/2014/01/math-talk-101
At this point we also developed an operation definition for weight. There are 2 choices: the force of the entire earth pulling down on the object or the force of the floor (or whatever support) pushing up on the object. Since a person's apparent weight can change in an elevator (& I totally need to try this, but I think the elevator at school might be too gentle), we went with the gravitational field strength of the planet. I've got "Is weight a property or an experience?" written in my notes but no discussion or conclusion for that particular question.
Next up, friction! Laura had us predict the force it would take to pull a heavy wooden block along a board. Then she did a demo with the force sensor graph displayed on the wall & the graph showed both a spike & a flat bit -- These values were named static or starting friction & kinetic friction. We came up with a list of factors that might affect friction -- Every group did mass of the block (a stand-in for the surface force) & then different groups got speed of the pull, surface roughness, & surface area of the block. For increasing surface force (that is, increasing mass) we found Fstatic = 0.41 Fsurface & Fkinetic = 0.28 Fsurface. All groups found that static force was greater than the kinetic force. The other variables were not as clear: There was no relationship between the force of friction & surface area (shocking!), there was definitely a relationship between the force of friction & the texture of the surface (think ice rink), & the apparent relationship between force of friction & speed might be more due to pulling with more force. The coefficient of friction (the numbers in the 2 equations above) is called mu (the Greek letter that looks like an "m" with a tail) ... & that's for both the static and the kinetic situations. That's not confusing at all! Grr, my proofreader soul is annoyed.
I raised the idea of van der Waal's forces playing a part in friction (https://www.youtube.com/watch?v=gzm7yD-JuyM) because that's something we talked about in one of my chemistry classes & because I'm a bio nerd & I love geckos.
For worksheet #2, I was in Don's group & he specifically talked about why they chose the problems to whiteboard (to cover all the conceptual ideas & skills) & which groups to give them to (match the problems to the capacity of the group). We also specifically called free fall acceleration the result of the force of the gravitational field strength. (This is something I have to remember.)
& then we moved into forces acting on two bodies attached in some way. The first drawing showed 2 carts attached by a spring & we had to figure out the force acting on each cart based on a 2 N pull. Them with a cart attached to a hanging weight (via a pulley), then 2 weights on either side of a pulley (an Atwood machine). We first treated both objects together as a system, then each object separately. The 90-degree turn made me a bit confused later on a worksheet problem, which just reinforced the fact that all models have limitations.
For worksheets 3 & 4, I finally got to facilitate a discussion. I need to not ask just "who has something different" because most students won't be brave enough to say. Corrine did a really cool thing (in the next session) where she asked somebody else to explain the group's board -- I'm totally stealing that. Other notes include adding "I've noticed" & "I'm wondering" as talk moves, using "hmm" to indicate wait time, & having groups who were in hot discussion explain what they were discussing. Dissecting the discussions -- what worked & what didn't -- is really helpful. People are getting better at including the group.
We also discussed if friction always opposes motion (it doesn't, think about something travelling in a pickup truck's bed) & how our model is just a dot representing the center of mass (as opposed to dimensional force models that include the object's structure).
To wind up the unit, our challenge was to land the hanging weight from a modified Atwood machine in the seat of a buggy. One of my group members was much stronger in physics than the other 2 & did most of the work for the challenge, without explaining it a lot. Part of that is the nature of the beast -- Don walks around urging us to go faster every freaking day, & explaining takes time -- but part of it is group learning vs individual learning. We're all great individual learners, we've been trained that way for 12+ years, & it takes attentiveness to break yourself out of that. I know I've been learning a lot from my partners...
Equipment List
Coin & Feather Vacuum Tube (because I can't take kids to the moon), $55
http://www.onlinesciencemall.com/coin-feather-free-fall-tube.html
Vacuum Pump (manual, vacuum thru 2 atmospheres), $35
http://www.enasco.com/product/SA08839M
Vernier USB-linked Motion Sensor (to hook to Chromebooks), $109
http://www.vernier.com/products/sensors/motion-detectors/go-mot/
Pulley (set of 5), $11.50
http://www.amazon.com/ETA-hand2mind-Single-Pulley-16150/dp/B008AK65J2
Mass Set (hanging), $16.50
http://www.carolina.com/mechanics-accessories/slotted-mass-set-with-weight-hanger/751442.pr
Mass Set (not hanging), $84
http://www.carolina.com/mechanics-accessories/slotted-mass-set-500-x-10-g/751447.pr;jsessionid=083B3E4597CBE358F73D7A8E9C875317.stageworker5?question=
Mini Dynamics Cart (pair), $22
https://store.schoolspecialty.com/OA_HTML/ibeCCtpItmDspRte.jsp?minisite=10029&item=2588904
The 2 videos we watched were both about growth mindset. (There are bunches & I can't find the exact ones we saw.) This is Carol Dweck's idea & it's all about praising the effort, not the intelligence. In fact, when you praise a kid for being smart, you set them up for failure -- When they struggle, they feel dumb; when they struggle, they give up; when they struggle, they go back to the easier situation where they were "smart". When you praise the effort, they try harder things. So this is a book (http://www.amazon.com/Mindset-The-New-Psychology-Success/dp/0345472322) that I'll need to read, hopefully before the summer's over.
But the "student mode" unit started with us trying to apply constant force to the hover car. By the end of the 3rd table, we were running!
Then we had a pair of experiments -- what's the relationship between force & acceleration & what's the relationship between mass & acceleration? (We talked about ramp angle but decided that would be confounding so we kept the tracks flat.) So we set up our track with a motion sensor & had one person push the cart along with a spring scale, increasing the force each time. We ended up with a = 0.91F. Next we had that same person push the cart along, increasing the mass each time. We ended up with a = 0.56 (1/m).
Don led a discussion (he was at the front board) where we linked up the formulas from these 2 experiments. He combined the 2 equations into a = __F/m & we plugged data in from our experiments to figure out the missing coefficient. (Our group came up with 0.8 & 0.86, using a 1 kg cart being pushed at 1 N & 1.5 N.) Then he listed the coefficients the groups came up with, which ranged from 0.85 to 1.4. Since nature doesn't use random numbers (& since all the pushers had noted how hard it was to push with a constant force, even for less than 2 meters), we went with a coefficient of 1, which means we came up with this final equation: a = F/m. (It's important to note here that F is the unbalanced force, or Funbal. Curse this blog program for not doing subscripts!) This is Newton's 2nd law, written out with the causes of change on one side & what gets changed on the other. This made a lot more sense to me than how Arons showed it in his chapter.
Pushing with the spring scales reinforces the concept of what a force is -- a push or pull. I really need to get some push-&-pull spring scales. Again, it's a shame that I had to turn in my budget at the end of the school year -- There's definitely stuff I would swap out now. (Altho I am pretty excited about dissecting hearts next year.)
We also discussed units, because they get messy here. Acceleration is measured in m/s/s, force is measured in N, & mass is measured in kg. So a kilogram is a measurement of an object's resistance to motion & a newton is a measurement of the force required to accelerate a 1-kg object to 1 m/s/s. (Don threw in "sticks, bricks, & clicks" as an alternative measuring system, just to rub it in how arbitrary measurements are. I need to find a good history of the metric system...) We were advised to not make a big deal about it, unless students asked. So we'll see how that goes. :-)
To help solidify our understanding, Don drew a picture of 2 people pulling on a skateboarder, one with 100 N of force & the other with 120 N of force. Which way does the skateboarder go? In the direction of the unbalanced force. & then he had us imagine the forces in an elevator & where they were balanced vs unbalanced (& how we felt). The most important thing here is that we don't feel the force of the entire earth pulling us down, only the force of the floor pushing us up. (That's an interesting biology fact.) & then we did worksheet #1.
From this point on, for every worksheet, we divided up into 2 smaller groups & practiced leading discussions. We used the list of talk moves from the Talk Science Primer & the bookmarks from Laura. This apparently is what people say is the biggest lack -- not enough practice leading discussions. (Which is probably why the chem group started leading discussions pretty early on, at least if I'm interpreting their tweets correctly.) So this was good practice -- most people questioned the people who worked on the problem great but didn't necessarily include the rest of the group, which is pretty standard teaching-as-is-done-currently -- but it also ended up being an interesting sociological observation. When the facilitator called on people to lead the discussion, who did they pick & why? When people just volunteered, who was it & why? The class was 50-50 male-to-female but it was mostly the guys who volunteered (or were called on, depending). Were the guys more experienced physics teachers & so more willing to take risks & practice facilitating? Were the guys just more willing to take risks regardless? Did facilitators call on people they spent "after school" time with? So, maybe not what I was supposed to learn but I did get to observe & practice my talk moves too. Here's a link to a math version of the talk moves: http://www.scholastic.com/teachers/top-teaching/2014/01/math-talk-101
At this point we also developed an operation definition for weight. There are 2 choices: the force of the entire earth pulling down on the object or the force of the floor (or whatever support) pushing up on the object. Since a person's apparent weight can change in an elevator (& I totally need to try this, but I think the elevator at school might be too gentle), we went with the gravitational field strength of the planet. I've got "Is weight a property or an experience?" written in my notes but no discussion or conclusion for that particular question.
Next up, friction! Laura had us predict the force it would take to pull a heavy wooden block along a board. Then she did a demo with the force sensor graph displayed on the wall & the graph showed both a spike & a flat bit -- These values were named static or starting friction & kinetic friction. We came up with a list of factors that might affect friction -- Every group did mass of the block (a stand-in for the surface force) & then different groups got speed of the pull, surface roughness, & surface area of the block. For increasing surface force (that is, increasing mass) we found Fstatic = 0.41 Fsurface & Fkinetic = 0.28 Fsurface. All groups found that static force was greater than the kinetic force. The other variables were not as clear: There was no relationship between the force of friction & surface area (shocking!), there was definitely a relationship between the force of friction & the texture of the surface (think ice rink), & the apparent relationship between force of friction & speed might be more due to pulling with more force. The coefficient of friction (the numbers in the 2 equations above) is called mu (the Greek letter that looks like an "m" with a tail) ... & that's for both the static and the kinetic situations. That's not confusing at all! Grr, my proofreader soul is annoyed.
I raised the idea of van der Waal's forces playing a part in friction (https://www.youtube.com/watch?v=gzm7yD-JuyM) because that's something we talked about in one of my chemistry classes & because I'm a bio nerd & I love geckos.
For worksheet #2, I was in Don's group & he specifically talked about why they chose the problems to whiteboard (to cover all the conceptual ideas & skills) & which groups to give them to (match the problems to the capacity of the group). We also specifically called free fall acceleration the result of the force of the gravitational field strength. (This is something I have to remember.)
 |
| This problem was solved 2 different ways! |
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| A 2-cart system. (Really, there is a string between them.) |
 |
| Sorry, I can't make it flip. :-( |
This is how you introduce an Atwood machine. :-)
For worksheets 3 & 4, I finally got to facilitate a discussion. I need to not ask just "who has something different" because most students won't be brave enough to say. Corrine did a really cool thing (in the next session) where she asked somebody else to explain the group's board -- I'm totally stealing that. Other notes include adding "I've noticed" & "I'm wondering" as talk moves, using "hmm" to indicate wait time, & having groups who were in hot discussion explain what they were discussing. Dissecting the discussions -- what worked & what didn't -- is really helpful. People are getting better at including the group.
We also discussed if friction always opposes motion (it doesn't, think about something travelling in a pickup truck's bed) & how our model is just a dot representing the center of mass (as opposed to dimensional force models that include the object's structure).
To wind up the unit, our challenge was to land the hanging weight from a modified Atwood machine in the seat of a buggy. One of my group members was much stronger in physics than the other 2 & did most of the work for the challenge, without explaining it a lot. Part of that is the nature of the beast -- Don walks around urging us to go faster every freaking day, & explaining takes time -- but part of it is group learning vs individual learning. We're all great individual learners, we've been trained that way for 12+ years, & it takes attentiveness to break yourself out of that. I know I've been learning a lot from my partners...
Equipment List
Coin & Feather Vacuum Tube (because I can't take kids to the moon), $55
http://www.onlinesciencemall.com/coin-feather-free-fall-tube.html
Vacuum Pump (manual, vacuum thru 2 atmospheres), $35
http://www.enasco.com/product/SA08839M
Vernier USB-linked Motion Sensor (to hook to Chromebooks), $109
http://www.vernier.com/products/sensors/motion-detectors/go-mot/
Pulley (set of 5), $11.50
http://www.amazon.com/ETA-hand2mind-Single-Pulley-16150/dp/B008AK65J2
Mass Set (hanging), $16.50
http://www.carolina.com/mechanics-accessories/slotted-mass-set-with-weight-hanger/751442.pr
Mass Set (not hanging), $84
http://www.carolina.com/mechanics-accessories/slotted-mass-set-500-x-10-g/751447.pr;jsessionid=083B3E4597CBE358F73D7A8E9C875317.stageworker5?question=
Mini Dynamics Cart (pair), $22
https://store.schoolspecialty.com/OA_HTML/ibeCCtpItmDspRte.jsp?minisite=10029&item=2588904
Sunday, July 5, 2015
Unit 4 -- Balanced Forces Are Balanced (& Diagrammed)
We started out with a video & discussion on class discussion & its goals. The hardest part, really, is for the teacher to let go the reins & trust students to have ideas. & of course the kids have to know how to discuss things, rather than arguing or letting other people do all the talking. Building that into the classroom culture will also be a bit of a challenge, at least the first few times. (My notes say "code switching", which I know Laura talked about, so that'll be another place to introduce that.) Classroom discussion can be broken into 3 main parts: giving students time to think, asking them to expand on their initial (& probably unformed) ideas, & having the other students repeat (& build on) ideas. A reading in Unit 5 (sorry, I'm jumping the gun), the Talk Science Primer, reinforced these ideas & introduced a variety of "talk moves". (Both the video & the reading came from this organization: http://inquiryproject.terc.edu/, altho I don't know who TERC is.) I've seen these talk moves in action during this workshop & in some of my grad classes (but not in my undergrad classes) & I've tried them -- rather ineffectually, I'm afraid -- last year. So, like Laura suggested, I'll have a copy of the talk moves on my clipboard & will give all of my students the bookmark version that was passed around in class. (One of the other modeling workshops is using the bookmarks too, at least according to a picture on Twitter.) Improving my classroom discussion skills is actually something that was in my end-of-year evaluation so it'll be nice to say "Hey look, not only did I improve my content knowledge, I improved my discussion leading knowledge." Now hopefully it works in real life!
Closely tied with classroom discussion are student misconceptions, better called preconceptions. Again, we had a couple of readings & videos -- Minstrell in particular seems to be an early proponent of uncovering & changing student preconceptions with classroom discussion. Lots of these "common sense ideas" were held by folks like Aristotle, way back before Newton figured stuff out -- These are not dumb ideas. Don also regaled us with first-person stories that he blatantly stole from other sources (he admitted it, & we had one of the stories in our readings). I'm not such a good storyteller but maybe I've got the increasing popularity of sci fi on my side -- Will students still believe gravity is caused by air pressure? Will anyone say that astronauts on the moon had no gravity but didn't float off because they wore heavy boots? I'm probably luckier than some of my workshop classmates -- I've only got a single physics class next year & it's, like, 15 kids. (The class list isn't posted yet so I'm not 100% sure of the numbers.) I also get to try stuff out in Physical Science in the fall before I've got Physics in the winter & spring.
This unit, unlike the others, didn't start out with an experiment -- It started out with a statement. The 1st rule of forces is that all forces must be applied by a real physical object made of matter. After a brief discussion where we listed all sorts of potential forces on the board (& yes, the Jedi mind trick was one of them), we whittled down the list of forces to a push or pull. (We're going to come back to gravity, magnetism, & electricity -- You can't hit people with these things or buy "a magnetism" in the store so...) This is the start of our model so far -- We added statements over the course of the unit (& added a bonus one in Unit 5).
Laura introduced us to schema, a tool for figuring out which forces are acting on whatever our object is. (It looks a lot like a concept map, with words in circles connected by either solid or dotted lines.) So for a book in her hand, the items on the schema might be book, hand, air, & entire earth. We had a big discussion about if the air was exerting a force on the book & if so, in what direction. We calculated that the air pressure on the surface of a standard book (about the same size as standard paper) was as much as an elephant standing on it ... only Laura picked up that elephant with ease. So we decided that air pressure had to be coming from all sides equally & so cancelled itself out. (The exceptions would be really strong winds, like when you have your hand out a car window, or suction cups, where there's no air underneath.) This left us with the force of the hand on the book, a solid line, & the force of the entire earth on the book, a dotted line. If there are 2 lines in the schema, there are 2 lines in the force diagram. So from the dot in the middle of the book, there's one line up, representing the force of the hand, & one line down, representing the force of the entire earth. We did not use the word gravity here. In fact, we didn't really use gravity the whole entire unit. ADD TO MODEL: System schema are a good tool for force diagrams
Our next schemas involved a bowling ball on the table, then a tennis ball on the table. The big question here was how did the table know how much force to push up with. A brave volunteer from the audience went up & Laura put items into his outstretched hands -- He wobbled a lot more with the heavy book than with the buggy, & he wobbled a lot less 2nd & 3rd times the book was put in his hands. People can learn but inanimate objects can't, so Laura continued the demonstration with a bed spring & a big sponge -- They all adjusted to the equilibrium. She also had the floating magnets, which was really neat because the space between the bottom magnets got smaller & smaller as more magnets were added. So we talked about how the molecules in the table compress & rebound, like the spring or the sponge. ADD TO MODEL: at velocity = 0, forces are balanced
We also had a huge discussion over ground vs entire earth. We'll see if that comes up in my class.
Our next schema introduced the force sensor, in this case a spring scale calibrated in Newtons. Newtons were introduced as the unit of force with no definition provided, in keeping with the "vague enough to get started" theme. So on the block, there was the downward force of the entire earth & the upward force of the string. But it's the next example, the "hover car", that threw a monkey wrench in the works -- When it's sitting still, it's being acted on by the air pushing up & the entire earth pulling down, but what about when it's moving? Not when it's being pushed & set in motion, but when it's floating serenely across the table at a constant velocity? Surprise, it's still just the upwards air & the downwards earth. The video of the person on a horse dropping a cannonball (& the cannonball continuing forward if the horse was galloping along) goes here, but I can't find a link. ADD TO MODEL: when change in velocity = 0, forces are balanced (in vertical or horizontal directions)
Our next schema was pushing a book across a table. Now the schema has 2 lines between the book & the table -- 1 for the upwards force & 1 for the sideways force. (Just like we aren't saying gravity, we aren't saying normal force or friction. Laura says we can use nicknames once we know the forces better. That's a really good way to say that.) She had us put 2 dry-erase erasers together & watch how the fibers stuck together & made it hard to slide the erasers. She also had 2 hair brushes to show the same effect. Since we don't have electron-microscope eyes, this is our analogy. When to include the anti-sliding force of the table? That depends on how the object is moving. ADD TO MODEL: acceleration is in the direction of the unbalanced force
We're building the idea of inertia here. The hover cars are really good for this, actually. We goofed around a little (Don started it) & tried to get the hover car to go all the way from the lunch area to the glass wall separating the offices, down the longest hallway in the building. We never managed to get it thru the door but it certainly went the whole way with very little loss of speed.
After solidifying our ideas with worksheet #1 (symmetry is our friend & angled forces can be broken into "shadow forces"), we finally got to do a hands-on activity! (This has been a much more "ideas only" sort of unit.) In our inquiry lab, we found the mass of a bunch of objects then used the Vernier force sensor to find the downward force of the entire planet. My group was a little rushed in finishing the whiteboard -- I got the slope upside down -- but it turns out that for every kilogram of mass, the entire earth exerts a downward pull of 10 newtons. Hmm... But we're still not calling it gravity. Instead, we're saying it's the strength of the gravitational field of the Earth. Specific is terrific. ADD TO MODEL: forces at an angle have horizontal & vertical components (the "shadow parts") ADD TO MODEL: 10 N/kg -- gravitational field strength
We also had a lot of discussion about the middle string, so Don put together a static demo during lunch.
So now the entire class tired to come up with an operational definition for "mass", without using the terms "matter" & "stuff". Which was really hard. Some groups used google but the definitions they found didn't help much. (My favorite was "how much an object weighs when there's no gravity", which Don didn't like at all.) Don had a demo with rolly carts, one with a heavy book & one without, & the one with more mass was harder to start and harder to stop ... but that was left to simmer. Instead, we did this: ADD TO MODEL: an object in motion stays in motion in a straight line at a constant velocity if the forces are balanced; an object at rest stays at rest if forces are balanced (Newton's 1st law)
"We're not done" is the nature of science & we'll be coming back to the issue of mass & weight. (The other noncontact forces -- magnetism, electrostatic, & strong -- are not in this workshop.) We've actually circled back to the "force field" idea of gravity -- the gravitational field of the planet -- which is pretty neat.
Before we tried worksheets 2 & 3, Laura wrote out the 5 steps for solving problems, of which "Follow the schema" is the most important. There were a lot more diagonal forces & I'm definitely stealing Laura's "shadow forces" demo. I haven't done enough math lately so I wrote SOH CAH TOA for pretty much every problem. What math will my Physical Science kids have compared to my Physics kids?
1) Write out the schema
2) Draw the force diagram
3) Figure out the "shadow components" of a diagonal force
4) Figure out where (or if) the forces are unbalanced, vertically & horizontally
5) Solve!
Talking over the problems on the whiteboards is pretty helpful. Choosing the right problems is also a skill I need to learn, or at least sharpen.
Then Don had a force demo & we got to do some hands-on stuff again. When I do this with my students, I'm sure I'll get complaints that suddenly the class is much more "notes"-y. Anyways, Don had somebody come up & hop on a force plate, which essentially acted just like a bathroom scale only read things in newtons & was connected to the computer. Then they did push ups. We talked a little about how the force line changed, & when. Then Don had 2 people, one big & one little, come up & do battle! Actually, they just banged the force plates together & pushed each other around. No matter what they did, the forces recorded by the force plates were the same. (There's a really cool video about equal forces but unequal effects, the cars with the band saw blades on them, but again I can't find the link.) So then each group tested this out, colliding carts equipped with force sensors in various ways. It didn't matter if we collided the carts head-on, while they were at different velocities, when they had different masses, on an incline ... Whatever we tried, the force on each car was exactly the same. ADD TO MODEL: all forces come in pairs that are equal in strength, opposite in direction, & act on the other object (Newton's 3rd law)
No matter what these guys did, the forces registering on their plates were always equal.
The discussion about force pairs was kind of interesting. Don put a block on a table & draw the force diagram. Then he asked if the diagram showed a force pair. Half the class moved to the yes side, half to the no side. I said yes, because the forces were equal & opposite. However, I wasn't thinking about the definition (they affect different objects) & the force diagram (which are the forces on a single object). The schema shows a single line between the block & the table & that represents a force pair but you'd have to draw 2 different force diagrams to show the same thing. This is something I'll try in class -- The whole "convince the other side to join you" was really useful. I'll have to be very careful about saying "action reaction" when I really mean "force pair".
At this point we've got 3 possibilities for what "weight" is: the force of the entire earth on the object, the force the the object on the surface, or the force of the surface on the object. We're leaving this until later -- O the suspense! :-)
We did a problem from worksheet #4 & measured out the forces & angles with a ruler & protractor. We came pretty close to the correct trig answer & I learned a new term -- fatty marker error. It will be helpful to know the "special" triangles when I assign students problems. Don had us set up an angled track with a cart on a string & measure the force on the string. As the angle gets closer to vertical, the force on the string gets closer to the "weight" of the cart. What goes from 0 at 0 degrees & reaches its maximum at 90 degrees (& then goes down again)? Sine! So the force on the string is represented by a sine function, which is pretty cool. (Again, what math level am I dealing with in my students?)
"But wait," you say, "what about Newton's 2nd law? That's totally missing!" Watch this spot! Acceleration coming soon!
Equipment List
Vernier Force Plate, for measuring the force of humans rather than little carts, $245
http://www.vernier.com/products/sensors/force-sensors/fp-bta/
Vernier Force Sensor, for measuring the force of the carts & small hanging things, $109
http://www.vernier.com/products/sensors/force-sensors/dfs-bta/
Double-ended Spring Scale, to measure both pushes & pulls, $10
http://www.teachersource.com/product/pushpull-spring-scales/lab-equipment
Big-faced Spring Scale, for classroom demos (we only have small ones), $45
https://www.enasco.com/product/SB21390M
Triple-beam Balance (we don't seem to have one, just electronic scales), $80
http://www.teachersource.com/product/adam-triple-beam/lab-equipment-balances
Big Protractor, for use by students (more accurate than clinometer apps?), $16
http://www.amazon.com/Westcott-School-Chalkboard-Protractor-Handles/dp/B001AZ65F8
Air Zooka, to hit kids with air, $20
http://www.teachersource.com/product/air-zooka/air-pressure
Hoover Car (OK, Hoover Soccer Disk), for balanced-forces-while-moving demo,
http://www.teachersource.com/product/air-soccer-disk-2014/air-pressure-general
Suction Cup Demo (it's just air pressure!), set of 3, $10
http://www.teachersource.com/product/lilsuctioner-package-of-3/air-pressure-general
Newton's Apple (it weighs a newton), $7 (or $30 for 6)
http://www.teachersource.com/product/newtons-apple/physics
"Force Pear", or at least the pear, $3
http://www.amazon.com/Pear-Artificial-Fruit-Kitchen-Decoration/dp/B000J56HLW
Helicopter Toys for Don's painful demo, $2 for 12
http://www.amazon.com/Fettipop-Plastic-Dragonfly-Assortement-Yellow/dp/B0035RRPJE/ref=sr_1_7?s=toys-and-games&ie=UTF8&qid=1436108776&sr=1-7&keywords=whirligig
Closely tied with classroom discussion are student misconceptions, better called preconceptions. Again, we had a couple of readings & videos -- Minstrell in particular seems to be an early proponent of uncovering & changing student preconceptions with classroom discussion. Lots of these "common sense ideas" were held by folks like Aristotle, way back before Newton figured stuff out -- These are not dumb ideas. Don also regaled us with first-person stories that he blatantly stole from other sources (he admitted it, & we had one of the stories in our readings). I'm not such a good storyteller but maybe I've got the increasing popularity of sci fi on my side -- Will students still believe gravity is caused by air pressure? Will anyone say that astronauts on the moon had no gravity but didn't float off because they wore heavy boots? I'm probably luckier than some of my workshop classmates -- I've only got a single physics class next year & it's, like, 15 kids. (The class list isn't posted yet so I'm not 100% sure of the numbers.) I also get to try stuff out in Physical Science in the fall before I've got Physics in the winter & spring.
This unit, unlike the others, didn't start out with an experiment -- It started out with a statement. The 1st rule of forces is that all forces must be applied by a real physical object made of matter. After a brief discussion where we listed all sorts of potential forces on the board (& yes, the Jedi mind trick was one of them), we whittled down the list of forces to a push or pull. (We're going to come back to gravity, magnetism, & electricity -- You can't hit people with these things or buy "a magnetism" in the store so...) This is the start of our model so far -- We added statements over the course of the unit (& added a bonus one in Unit 5).
 |
| The completed Model So Far |
 |
| sample of a schema from worksheet 1 |
We also had a huge discussion over ground vs entire earth. We'll see if that comes up in my class.
Our next schema introduced the force sensor, in this case a spring scale calibrated in Newtons. Newtons were introduced as the unit of force with no definition provided, in keeping with the "vague enough to get started" theme. So on the block, there was the downward force of the entire earth & the upward force of the string. But it's the next example, the "hover car", that threw a monkey wrench in the works -- When it's sitting still, it's being acted on by the air pushing up & the entire earth pulling down, but what about when it's moving? Not when it's being pushed & set in motion, but when it's floating serenely across the table at a constant velocity? Surprise, it's still just the upwards air & the downwards earth. The video of the person on a horse dropping a cannonball (& the cannonball continuing forward if the horse was galloping along) goes here, but I can't find a link. ADD TO MODEL: when change in velocity = 0, forces are balanced (in vertical or horizontal directions)
Our next schema was pushing a book across a table. Now the schema has 2 lines between the book & the table -- 1 for the upwards force & 1 for the sideways force. (Just like we aren't saying gravity, we aren't saying normal force or friction. Laura says we can use nicknames once we know the forces better. That's a really good way to say that.) She had us put 2 dry-erase erasers together & watch how the fibers stuck together & made it hard to slide the erasers. She also had 2 hair brushes to show the same effect. Since we don't have electron-microscope eyes, this is our analogy. When to include the anti-sliding force of the table? That depends on how the object is moving. ADD TO MODEL: acceleration is in the direction of the unbalanced force
 |
| This problem has both the anti-sliding force (note the 2 lines between desk & floor in the schema) & an angled force. |
After solidifying our ideas with worksheet #1 (symmetry is our friend & angled forces can be broken into "shadow forces"), we finally got to do a hands-on activity! (This has been a much more "ideas only" sort of unit.) In our inquiry lab, we found the mass of a bunch of objects then used the Vernier force sensor to find the downward force of the entire planet. My group was a little rushed in finishing the whiteboard -- I got the slope upside down -- but it turns out that for every kilogram of mass, the entire earth exerts a downward pull of 10 newtons. Hmm... But we're still not calling it gravity. Instead, we're saying it's the strength of the gravitational field of the Earth. Specific is terrific. ADD TO MODEL: forces at an angle have horizontal & vertical components (the "shadow parts") ADD TO MODEL: 10 N/kg -- gravitational field strength
We also had a lot of discussion about the middle string, so Don put together a static demo during lunch.
 |
| Here is the static demonstration. |
 |
| Here is the whiteboard with the problem. |
"We're not done" is the nature of science & we'll be coming back to the issue of mass & weight. (The other noncontact forces -- magnetism, electrostatic, & strong -- are not in this workshop.) We've actually circled back to the "force field" idea of gravity -- the gravitational field of the planet -- which is pretty neat.
Before we tried worksheets 2 & 3, Laura wrote out the 5 steps for solving problems, of which "Follow the schema" is the most important. There were a lot more diagonal forces & I'm definitely stealing Laura's "shadow forces" demo. I haven't done enough math lately so I wrote SOH CAH TOA for pretty much every problem. What math will my Physical Science kids have compared to my Physics kids?
 |
| This group used a property of a 30-60-90 triangle instead. |
1) Write out the schema
2) Draw the force diagram
3) Figure out the "shadow components" of a diagonal force
4) Figure out where (or if) the forces are unbalanced, vertically & horizontally
5) Solve!
Talking over the problems on the whiteboards is pretty helpful. Choosing the right problems is also a skill I need to learn, or at least sharpen.
 |
| This sets the stage for force pairs! |
No matter what these guys did, the forces registering on their plates were always equal.
The discussion about force pairs was kind of interesting. Don put a block on a table & draw the force diagram. Then he asked if the diagram showed a force pair. Half the class moved to the yes side, half to the no side. I said yes, because the forces were equal & opposite. However, I wasn't thinking about the definition (they affect different objects) & the force diagram (which are the forces on a single object). The schema shows a single line between the block & the table & that represents a force pair but you'd have to draw 2 different force diagrams to show the same thing. This is something I'll try in class -- The whole "convince the other side to join you" was really useful. I'll have to be very careful about saying "action reaction" when I really mean "force pair".
At this point we've got 3 possibilities for what "weight" is: the force of the entire earth on the object, the force the the object on the surface, or the force of the surface on the object. We're leaving this until later -- O the suspense! :-)
We did a problem from worksheet #4 & measured out the forces & angles with a ruler & protractor. We came pretty close to the correct trig answer & I learned a new term -- fatty marker error. It will be helpful to know the "special" triangles when I assign students problems. Don had us set up an angled track with a cart on a string & measure the force on the string. As the angle gets closer to vertical, the force on the string gets closer to the "weight" of the cart. What goes from 0 at 0 degrees & reaches its maximum at 90 degrees (& then goes down again)? Sine! So the force on the string is represented by a sine function, which is pretty cool. (Again, what math level am I dealing with in my students?)
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| Don's demo of the set up |
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| Force vs angle, 0-90* |
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| Our results |
Don also reinforced that the upward force of a surface, like the track, is perpendicular to that surface no matter what angle the surface is at. So if the track is angled, the upward force is also angled, at least with reference to the ground & downwards force of the entire earth. Heck, even walls have a perpendicular force. Sometimes it's better to have the surface be the "horizontal" & break the downwards force of the entire earth into its components.
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| This was also the "measured" & "fat marker error" whiteboard. |
The other videos we saw during the unit were more about how people learn. The effectiveness of science videos (https://www.youtube.com/watch?v=eVtCO84MDj8) was called into question (especially considering that Khan Academy is now the official provider of SAT prep videos) -- Unless the video starts with misconceptions, students don't listen because they think they already know. I've shown this video (bowling ball & feathers falling in a vacuum, https://www.youtube.com/watch?v=E43-CfukEgs) to my Physical Science kids; next time maybe I'll have before & after discussion to see how their ideas change. (Don only shows videos for engagement, & that might be the way to go.)
The format of school was considered in a video by a guy with a PhD about skateboarding & how he struggled for years to master a particular trick (https://www.youtube.com/watch?v=lHfo17ikSpY). (For some reason, I had never put "skateboarder" & "PhD" together in my head.) This ties right in with Laura's motto "There's no comfort in the learning zone & no learning in your comfort zone", only with bruises, cussing, & no real way to issue grades.
& then the format of math class, in particular math questions (& you could just as easily say physics questions), was examined (https://www.youtube.com/watch?v=NWUFjb8w9Ps). Most questions are way artificial & contain exactly what you need to know, rather than being grounded in real life & having not enough info & unnecessary details. The take-away from that video was "Be less helpful", which really is the theme of this whole workshop. I can certainly be less helpful but will it be in a way that helps people learn? Time will tell. :-)
"But wait," you say, "what about Newton's 2nd law? That's totally missing!" Watch this spot! Acceleration coming soon!
Equipment List
Vernier Force Plate, for measuring the force of humans rather than little carts, $245
http://www.vernier.com/products/sensors/force-sensors/fp-bta/
Vernier Force Sensor, for measuring the force of the carts & small hanging things, $109
http://www.vernier.com/products/sensors/force-sensors/dfs-bta/
Double-ended Spring Scale, to measure both pushes & pulls, $10
http://www.teachersource.com/product/pushpull-spring-scales/lab-equipment
Big-faced Spring Scale, for classroom demos (we only have small ones), $45
https://www.enasco.com/product/SB21390M
Triple-beam Balance (we don't seem to have one, just electronic scales), $80
http://www.teachersource.com/product/adam-triple-beam/lab-equipment-balances
Big Protractor, for use by students (more accurate than clinometer apps?), $16
http://www.amazon.com/Westcott-School-Chalkboard-Protractor-Handles/dp/B001AZ65F8
Air Zooka, to hit kids with air, $20
http://www.teachersource.com/product/air-zooka/air-pressure
Hoover Car (OK, Hoover Soccer Disk), for balanced-forces-while-moving demo,
http://www.teachersource.com/product/air-soccer-disk-2014/air-pressure-general
Suction Cup Demo (it's just air pressure!), set of 3, $10
http://www.teachersource.com/product/lilsuctioner-package-of-3/air-pressure-general
Newton's Apple (it weighs a newton), $7 (or $30 for 6)
http://www.teachersource.com/product/newtons-apple/physics
"Force Pear", or at least the pear, $3
http://www.amazon.com/Pear-Artificial-Fruit-Kitchen-Decoration/dp/B000J56HLW
Helicopter Toys for Don's painful demo, $2 for 12
http://www.amazon.com/Fettipop-Plastic-Dragonfly-Assortement-Yellow/dp/B0035RRPJE/ref=sr_1_7?s=toys-and-games&ie=UTF8&qid=1436108776&sr=1-7&keywords=whirligig
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