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! |
 |
| 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
No comments:
Post a Comment