Oh no you didn’t!

So I was relaxing, watching tv, and basically minding my own business.  Then it happened!  I saw the most offensive commercial I’ve ever seen.  I’m not going to give the company the time of day (I’m well aware the power my blog carries in the world) by naming them.  Needless to say, it was a company trying to entice people to receive help from IRS past taxes.

Here’s the kicker, a few seconds into the commercial, the spokesman (a cartoon of a classic nerd as the host) begins to explain how their company will lower your tax payments to the IRS.  Here’s what he writes on the whiteboard for someone that owes $20,000:

then:

followed by:

which magically makes the $20,000 become $1600!

I’m not sure which is worse, the fact that this company thinks that a “nerd” would write the above gibberish or that people will think this “magical” equations are the way for them to fix their problems.  I’m hoping Dan Meyer’s head is erupting right now!  (I say that knowing he probably won’t read this, and may, with his Jedi mind for math, just sense this atrocity of mathematics!)

Sorry to vent, thanks for making it this far, just had to get that off my chest.

The Atlantic-Pacific Rule

In preparation for this weeks Global Physics Department meeting, Andy has set up a online corkboard for people to begin sharing how they teach error propagation/analysis.  After briefly posting how I teach it, I thought it might be worthwhile to share in greater detail.

As an engineering major, I had my fair share of error anaylsis.  I think many of us High School teachers would agree that to get our students proficient in proper error analysis and propagation is not likely.  Although I feel the engineering way is a better method (ie: $4.2 \pm 0.3\, cm$), from my experience, HS students get lost in the numbers and miss the point.  Getting them to then use something like this is basically impossible:

$\large \sigma_f = \sqrt{\left(\frac{\delta f}{\delta a}\sigma_a)\right)^2+\left(\frac{\delta f}{\delta b}\sigma_b)\right)^2}$

Moreover, I don’t think a HS physics student needs that level of sophistication for their error analysis.  A practicing engineer, with lives in his or her hands, absolutely, but a student just being introduced to the idea, I don’t think so. 
 
So instead, I build off what my school’s chemistry teachers do.  One of their fundamental aspects is the beginnings of error analysis and propagation: writing the measured value with the correct significant figures (SigFigs), and knowing how to determine the number written by others. For this, instead of the traditional rules for reporting numbers with SigFigs, they use the Atlantic-Pacific Rules, which goes something like this:

Imagine the measured number is written such that the outline of the United States is surrounding the number:

You then ask yourself a series of questions:
1. Is the decimal point Present or Absent?
     – If the decimal point is Present, start from the Pacific side; if it is Absent start from the Atlantic side.
2. Once you have identified from what “side” of the number you start,
     – begin by counting the first non-zero number.  Count that number and every number that follows it.
3. The right-most SigFig is the uncertain digit that was estimated.

For the number above, since the decimal is Present, start from the Pacific side and count left to right.  The first non-zero number is “1” and if you follow through, there are 4 significant digits with the 0 (to the right of the 7) as the estimated digit.

For the number “$549,030,000” the Atlantic-Pacific Rule would tell you that there are 5 SigFigs with the 3 being the uncertain digit (decimal point absent, so you begin from the Atlantic Ocean side and count from right to left).

From my experience, this Rule gives all the same results of the typical rules found in most texts.  However, I find that students can remember this much easier, many liking the visual aspect of the rule.  If you’ve never seen this before, maybe give this a try.

Parent Letter – First Draft

After talking with some in my admin, we decided it might be a good idea to send a letter the parents of my new students to prepare them for a guided inquiry based class.  My hope is to not make it full of teacher talk, but a quick, concise preview to prevent the complaint, “He doesn’t teach anything.”  Any feedback would be greatly appreciated:

Dear Parents and Guardians,
    I would like to take this opportunity to welcome your son or daughter to my physics class. Physics is a challenging subject, that unfortunately, brings negative perceptions for many people. I wish this was not the case, as physics is a fascinating class and the foundation for all of science and engineering. Over the last several years, I have continually asked myself, “How can I better teach this course?” Luckily, many other Physics teachers have asked this very same question, and they have actively researched the answer. What the research is showing is that physics teachers need to stop talking about  physics, and start helping their students do physics.

One quirky way I’ve seen this transition described is the teacher needs to change from being a “Sage on the Stage” to a “Guide on the Side.” What I mean by that, is research shows students need to be actively engaged in deductive reasoning to determine the laws of physics from experiment rather than passively listening to a teacher describe those laws. In the process of helping students do physics, those students learn better problem solving skills, critical thinking skills, and communication skills. Unfortunately, most students haven’t been exposed to learning through guided inquiry, so many students feel uncomfortable early on. For most students, this discomfort eases part way through the first quarter. If your son or daughter feels lost at any point, please have them come and see me, and I will be happy to do what I can to help them.

In the end, my hope is to create an interesting and enjoyable way for your son or daughter to learn physics. I continue to try to find better ways to try to do that. Along the way, I hope your child will learn skills essential for college and their future job, even if he or she has no interest directly in the subject of physics. Who knows, maybe your son or daughter will decide that pursuing a career in physics is for them too!