Day 122: Hit Me With Your Best Shot

Wednesday, 26 February 2014

One lab group getting the horizontal velocity of their projectile.

One lab group getting the horizontal velocity of their projectile.

One of my four classes started their projectile motion lab today. The lab is called Hit Your Teacher in the Face, but I think I’ll change it next year to Hit Me With Your Best Shot. They’re trying to hit me right on the nose:

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I give them a ramp (actually, right angle moulding), a steel ball bearing, and a meter stick. I ask them to decide what info to measure and how to do it. They’re not allowed to send the ball bearing off the table before calling me over. Here’s one group doing the testing:

My colleague uses carbon paper to get a better mark of the initial impact location. She’s much smarter than me, who tries to eyeball it.

Day 121: Test Review and Robotz

Tuesday, 25 February 2014

Assembling the practice robot.

Assembling the practice robot.

The day started with official news that next January, I’ll be team teaching Introduction to Engineering with a math colleague and robotics co-coach. The course will be an intensive 3-week event. The course was originally designed to support our robotics program but necessarily needed to grow in scope for better registration appeal. Shaffiq and I are looking to Project Lead the Way for much of our inspiration.

I have kinematics tests coming up over the next two days and the kids need practice beforehand, so I opted to move a lab planned for today to test review instead.

Do everyone’s kids mix up the constant velocity, constant acceleration, and projectile motion problems when they get to test time? I’m seeing kids come to me wanting to apply d=rt to falling objects. (For the record, we don’t use d=rt. It’s been ingrained in them for so long they always want to quote it.)

I tried this year to get the kids to always add a few words on when an equation applies (and when it doesn’t) to their formula sheets. Many aren’t writing this down, though the formulas have been on the board for weeks with that info. For instance, Δx=vΔt should have next to it something like “for constant velocity or average velocity situations only”. I like the concept but need to figure out how to execute on it better.

Meanwhile, at robotics, the team’s goal today was “get the practice bot fully functioning with intake, winch, shooter, and all bits together”. At the end of the night, we were certainly closer but still not holding a functional practice robot. Our drivers desperately need practice and I’m getting nervous — our robot goes onto the trailer in a little over a week for our first competition.

Day 120: Projectiles Redux

Monday, 24 February 2014

Watching the "Bullet Dropped vs Fired" investigation on Mythbusters.

Watching the “Bullet Dropped vs Fired” investigation on Mythbusters.

I admittedly rushed the heck out of projectile motion this year. But I did it intentionally to stay on schedule with finishing the year with forces, energy, and momentum. We solved only problems with objects launched horizontally. A few of my classes got to watch parts of the Mythbusters episode called “Knock Your Socks Off”, which included the Bullet myth. I put together a playlist that includes the relevant parts. If you’re pressed for time, you could watch just parts 1, 4, and 5.

Kids still want to believe that the fired bullet will stay aloft longer. A few told me outright they didn’t believe the results. We drilled into why they felt that way and I learned they’re assuming you fire the gun at least a little above horizontal.

Day 119: Wile E Coyote

Friday, 21 February 2014

We’re having to fly through projectile motion because of time constraints. Today, I introduced the topic and we practiced a few problems to get the general idea. I’m constraining the topic to projectiles launched horizontally. The above Road Runner clip illustrates the independence of horizontal and vertical motion. Wait, what? That’s not how the real world operates? Dangit! We watched the clip, laughed, then introduced real projectile motion.

Here’re two examples of the types of problems my kids will be able to solve:

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Example problems for projectiles launched horizontally.

Day 118: A Little Knowledge

Thursday, 20 February 2014

You ever teach that kid, the one who has read ahead in his big sister’s calculus book, who’s forever watching Discovery channel on modern physics, who’s always asking for more detail than anyone else in class wants? Yeah, him. He’s a student in the classroom next door to mine. Yesterday, he swung by my room because his teacher had gone home for the day.

He brings me this:
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The kid disagreed with his teacher but didn’t understand my colleague’s reasoning.

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At this point, I think I’ve made some headway with the kid. He gets it physically, nothing can travel a finite distance in 0 time. But he’s still stuck on that function on his graph being f(x) = 1/x. So I bust my math teacher moves on him:image

imageI’m convinced that math and physics teachers should talk more than they currently do. The only way I could think to explain this kid’s conceptual mistake (the asymptote is at y=0) was through both physical means (nothing can travel somewhere in 0 time) and correct his mistake was through mathematical means with a function transformation.

Oh, and yes, I really did write out that conversation after he left the room. It was too rewarding for me to forget.

Day 117: Vectors

Wednesday, 19 February 2014

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Medium-level difficulty classwork problem on vectors.

Classwork today was way too difficult for the kids and that one thing threw the entire lesson off.

Background:

  • the students are freshmen, enrolled in a geometry class
  • earlier this semester, they learned vectors in math class
  • earlier this year, they learned trig ratios, special right triangles, and laws of sines and cosines
  • I have not emphasized unit conversions this year

So, after a quick refresher on some vocabulary, especially component and resultant, I handed out a classwork problem set for them to practice with. Right away, I could see the wheels coming off my lesson. Kids struggled with finding the distance traveled by a constant velocity object given a velocity in km/h and a time traveled in seconds. Then they struggled to extend their knowledge into finding resultant displacements for the sums of two vectors.

Where did this assignment go wrong?

  • it didn’t scaffold appropriately: there weren’t any easy problems to build confidence on and the problems got way too hard way too fast
  • there was unnecessarily difficult language and situations (most of these problems came from a problem workbook from the Holt Physics text)
  • the refresher lesson didn’t adequately prepare students for vector triangles that represented anything but displacements
  • too many unit conversions!

So, in a teacher move I ripped off a Dan Meyer post a few years back, I put a few notes on the Word doc so I’d know how to modify the assignment next year:

"Stickie" note reminder to myself before I reuse this next year.

“Stickie” note reminder to myself before I reuse this next year.

I’ve always beat myself up over not stretching the top students in my class and have to compliment myself on doing so with this assignment. At the expense of everyone else. Now, how do I maximize the stretch for some and minimize the stress for the others? Problem choice is one method I’ve considered.

Day 115: Your Consequence

Monday, 17 February 2014

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A former colleague of mine has this sign in her classroom: “Your consequence for not doing the assignment is doing the assignment.” This post is about that sign’s message.

About a third of my students blew off their snow day assignment from last week. Only one had a really good excuse — his power was out for the entire 48 hours we were out of school. So, after consulting with my department chair, I “invited” them all to spend office hours with me Monday and Tuesday to make up for the time they didn’t give me over the snow days. Here’s the email I sent:

Because you didn’t complete your snow day assignment, I need you to attend office hours after school on Monday and Tuesday to make up both the time and the assignment. You owe me a total of 60 minutes missed class time plus a completed assignment. Even if you complete the assignment before Monday, please report to my room.

I appreciate my department chair’s idea because it respects the kids who did their work and doesn’t get me into a blame game with those who didn’t. Most kids didn’t have a valid excuse, so this is kind of like a detention for them. 

Days 112-3: Reading Python

Wednesday, 12 February and Thursday, 13 February 2014

assignment

I haven’t taught my kids the first thing about coding. If they know something from previous learning, I’d be surprised. So, before winter storm Pax bore down on Atlanta, I had the kids install python and visual. Late Tuesday night, I sent them a remind101 text message to check on the assignment on our Moodle site.

The kids had to watch the video and answer the questions I asked:

  1. When writing computer programs (“code”), what is the purpose of a comment? 
  2. What symbol marks the beginning of a python comment?
  3. According to the script around line 70, W = -ball.m*g. Using values from earlier in the script, what is the weight of the ball we’re modeling?
  4. Also according to the script around line 70, Fd = -b*ball.vel. How would you expect the drag force to change as the ball’s velocity increases? (What is this kind of mathematical relationship called?)
  5. Something special is happening around line 73: ball.vel = ball.vel + g*deltat. It might look like bad math to you. So it’s a good thing it’s not math but code! This line means take the old ball velocity, add g*deltat to it and store it in the new ball velocity. In code, that equal sign is called an assignment operator. Which kinematics equation does this most closely represent?
  6. Around line 77, this: t = t + deltat. Based on what you just learned above about assignment operators (=), what’s happening here?
  7. Line 66 is the beginning of a loop. It says “as long as the time is less than 0.5s, keep repeating this section until the indented code ends. Look inside the loop (the indented stuff) and tell me what you see happening there.
  8. Given that deltat is 0.001s and the while loop says “while t<0.5”, how many loop repeats do you think will occur?

The toughest question proved to be 7, probably because I asked them to actually think on this one. Here’s my favorite response:

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In question 4, I asked how the drag force varies with a ball’s velocity. The code says Fd = -b*ball.vel. Most kids had the right idea, along the lines of this one: “as the ball’s velocity increases, the drag force would also increase, this is a positive correlation.”

The last question asked how many times the while loop would be repeated. The code said “while t<0.5, with increments of 0.001 from an initial value of 0”. So the correct answer is 500 (or 0.5/0.001). Probably 90% of the kids got this one right! Remember, they’ve never seen code before.

This assignment is phase one of my computational modeling work I’m doing with the help of the Georgia Tech PER Group.