All charged up

I've spent about 3 hours today thinking about the electric field created by two like charges.  I didn't spend all that time thinking about it because it's a particularly interesting topic, nor is it terribly hard for me to envision.

I spent the time thinking about it because I want a good image of the field that is a.) useful for my students and b.) available for me to use without bending any copyright laws.  I've been mostly generating my own artwork for classes (with the side goal of creating a CreativeCommons licensed library for people to make use of) but creating an electric field diagram isn't something that can easily be whipped up in a drawing program.

After quite a bit of searching for images labeled for reuse, I happened to find a python program that can be used to create vector field plots of various electromagnetic configurations. Awesome, right?  I even found an example code of the field that is generated by one positive and one negative charge.

What I wanted was the field around a set of like charges, but I can read source code and figure out how to change a negative sign, right?  Wrong.  I need to spare myself the embarrassment of posting my attempts to correctly plot the field, but know that it went from bad to worse.

Not willing to give up, I went back to wikimedia and found every uploaded image which had been made using this program. Fortunately, this included the charge configuration I was looking for:

Unfortunately, I wasn't too thrilled with the horizontally oriented field line right in between the two charges.  The electric field is zero at a point equidistant from the two (identical) charges. And while, the arrows are pointing in opposite directions along this line, I'm not sure if it is obvious to my students that the electric field at that point is zero.

(Side note: I'm starting to see why Randy Knight uses vector field plots, instead of electric field lines. We're not using the Knight textbook, and these drawings are my attempt to bridge the gap between the two representations and hopefully make things more understandable.)

What I'm going to do, unless I come up with something I like better, is use this image instead:

Gone is the electric field line in the middle and added are more vectors.  It's not perfect, but I'm not sure I can spend more time finding the perfect representation anymore.

Cubicle Warfare: 101 Office Traps and Pranks by John Austin

My rating: 3 of 5 stars

Like most books that are a list of pranks and practical jokes, this is a really quick read. While it had a few offensive (and possibly illegal?) suggested practical jokes, most of them were good natured and harmless office stunts. I got a few good laughs from some of the suggested pranks. It is a better book than some of the other similar books on pranks, but overall I was a bit disappointed with it.

What I learned about teaching this quarter

Another quarter has come and gone already. At the end of each term, I like to look back at what I've tried to do in the class and figure out what worked, what didn't work, and what I can do to improve for the next quarter.

What worked:

"Reading Quizzes" due at 8:00 am every day of class.  Okay, I'm still not convinced that the students are actually reading the text as much as I want them to, nor do I necessarily like calling them "Reading Quizzes" but I do get great information about what is generally the most confusing aspects of the material that we are going to cover.

I'm going to try to improve these by off-loading some of the clicker questions onto the "Reading Quizzes" in an attempt to make students confront their misconceptions and gaps in understanding.

What didn't work so well:

The Interactive Lecture Demonstrations were not as effective as I had hoped.  They took too much time and the payoff wasn't what I was hoping for.  I may try a few more, but I'm also thinking that I need to attend one of their workshops to see how to do them better in class.

What I learned:

I had a rough Fall quarter.  At the end of that quarter I felt that I knew less about teaching than I did at the start of the quarter. Part of the reason I reflect on what I've learned about teaching each quarter is an attempt to get better at teaching.  Before last Fall, every single term I had taught I felt like I was carrying forward lessons which I had learned and was therefore becoming a better teacher.  But my Fall quarter was pretty much the opposite of everything I had ever before experienced.  Strategies which worked well in the past crashed and burned. Students were frustrating and became closed to trying new ways of learning.  I tried adapting, I really did, but in the end I felt like the students and I were just surviving the class and each other.

This past quarter was a much better experience. True, the classes were smaller, probably in part due to the students wanting to get as far away from a bad teacher as possible. The students who remained were more willing to engage in the material and I feel that the class got deeper into the material this quarter than last.

I hadn't changed much in the way of what I was doing in class.  There were a few minor tweaks here and there, but overall the class was largely the same experience.  As this Winter quarter was drawing to an end I was trying to figure out what I had learned about teaching that would carry forward to next quarter. It was then that I realized the main difference between the two quarters was that somehow I had connected with the students in the Winter in a way that I had not in the Fall.

I'm still not sure what the difference was in HOW I connected with these students.  The point is that, when there was no connection, the class was disengaged and uninterested in learning. The more connected I felt to the class, the more willing to engage with the material they seemed to be.

It seems so obvious now that it is almost silly that I had to learn this lesson for myself.  I know in previous environments I've been in it has been easier to connect with students.  I don't know why it was harder last Fall, and in a sense it doesn't really matter.  I just need to remember to be cognizant of how the class is getting along with me so that we can't concentrate on learning.

Sign of Spring in Chicago

Back in my day we had to DRAW the Chladni patterns

Adopting the "growth" mindset

I just finished reading Mindset: The New Psychology of Success by Carol Dweck.  It has changed a lot about how I think about learning and personal growth in my life (both professionally and otherwise). I'm trying to implement the idea of having a "growth" mindset in all I do for my classes and my research.  It's hard work, but I guess that's part of the point.

If there was only one thing I could implement in my classes from the book, it would be the following passage from chapter 3:

How teachers put a growth mindset into practice is the topic of a later chapter, but here's a preview of how Marva Collins, the renowned teacher, did it. On the first day of class, she approached Freddie, a left-back second grader, who wanted no part of school. "Come on, peach," she said to him, cupping his face in her hands, "we have work to do. You can't just sit in a street and grown smart....I promise, you are going to do, and you are going to produce. I am not going to let you fail."

Robert Talbert recently asked about the responsibilities of students and instructors in college. I don't know if I have a set answer to his question, but I do believe that if students are willing to put in the effort to do the work that I ask them to do in my class, then it is my responsibility to provide whatever assistance they need to be successful in learning the content in my class.

You've seen the videos that Vi Hart has been producing featuring what she calls doodle games related to various topics in math, right?  They made the rounds of the science and physics blogs towards the end of last year and beginning of this year.

Here's one of the most popular videos, in case you haven't seen it:



I don't want to sound too critical of what this woman has produced.  In fact, I really like her series of videos. (Plus, she makes homemade musical instruments. How cool is that?)

But, here's what you might not know about Vi Hart: her father is George Hart, a former professor at Stony Brook University, a sculptor, and the first director of the soon-to-open Museum of Mathematics.

What that means to me is that Vi grew up in an environment where curiosity about mathematics was nurtured and developed. It also indicates to me that she has been working for a long time to develop her talents. Those last two points are not criticisms, they are merely observations. 

I do take issue with her underlying commentary on the state of math education (and really, school in general) which is that classes are boring and taught by incompetent teachers, and that students would get more out of class by not paying attention and just playing some doodle games. I'm not even sure I disagree with her (completely) on those points, either. What I disagree with is the notion that anyone learns anything from watching her videos. She talks too fast for most people to be able to maintain comprehension all the way through the video and there are many terms which are unfamiliar to non-mathematicians which fly by as the video is playing.

I wanted to better understand what the doodle games were all about, so the first thing I did was I tried creating some doodles on my own.  (If her only goal in these videos is to get people to try out the doodles, then maybe they are working better than I give her credit for.) I was able to follow the first two doodle games in the above video, but I wasn't able to get the shading right on the third doodle game. More frustrating to me was that I couldn't really understand the importance of the doodles. In the video she mentioned knot theory and weaving but I could never quite catch what it was she was actually saying about all of that.

I went looking for a transcript of the video, but I couldn't find one. So, I sat down at my computer and banged out a transcript myself. I learned a few things by doing that. One, I learned that one of the figures she mentioned in the video is called a Ouroboros. I had no idea what she was talking about when I had watched the video, but by piecing together the transcript I was able to get the correct spelling and look it up online.

After I had the transcript complete, I started looking into all the topics she mentioned in the video. My digging eventually turned into this post at metafilter which was well received by the community over there. In finding the links which went into the post, I was able to dig a little into topics like knot theory and topology which I had previously known next to nothing about. I definitely appreciate that the video brought these ideas to my attention so that I would be inspired to learn more about them.

The thing is, though, it took a lot of my time to read up on those topics. I was constructing the metafilter post for over 2 weeks, working an hour or two every night in my free time. I learned a lot because I put in the effort to do so. I'm willing to bet that Vi Hart has put in thousands of hours of study to cultivate her passion and talent for math. It seems a little disingenuous to me, then, that she puts together videos with the attitude of "classes are boring" and "students don't need to pay attention". For a lot of students, classes are their only chance to engage with topics such as math or science. Most people aren't fortunate enough to have a parent who is a professional scientist or mathematician. It might not appeal to adults who feel they suffered through boring classes in their school years, but how many more kids could she encourage to engage more in their classes if her videos said something like: "Hey, ask your teacher in class about this. If you show interest in it, your teachers will likely respond to that interest!"

But, more importantly, it would be great to remind students that learning takes work. You don't become an expert on graph theory just because you've watched a four minute video on doodles. This is something I know, but I have to constantly remind myself of anyway. If I really wanted to make the third doodle game work, I could do it, but I would have to put in the effort and time to be able to do it. Vi Hart's videos not only miss the opportunity to encourage students to think that way, they might be inadvertently sending students the exact opposite message.

Busses stuck

Falling ice messed up afternoon rush traffic in the loop today.

New toys for a nerdy boy

Close-up of tonight's utensils

Renae brought home sushi for dinner tonight

Still lots of foam

I tapped a new keg tonight after cleaning the lines. It's still really foamy, although not as bad as the last keg.

Navigating the roundabout

This sign amused me on the way to the dentist today.

Random links

My browser tabs are over-cluttered with stuff I've been thinking about for awhile.  I need to clear them out so I can focus on other ideas.  Here's what I've been meaning to write about, in no particular order:


Back in October (!) I came across this commentary on the documentary "Waiting for Superman". The meat of the article is in this quote:

Where did you think great teachers come from? That they spring fully formed from the head of Zeus? Just about everybody who’s an accomplished teacher used to be an ineffective teacher, and as the maker of a documentary about first year teachers, I’m totally confused that you don’t seem to understand this. If you want to talk about great teachers, but don’t have anything to say about the conditions under which teachers become great, you are at a different stadium than where the game is happening.
(Hint, by the way: in order to become great, teachers need to make and then learn from their mistakes. What kind of environment fosters making and learning from your mistakes? Fear that you will lose your job over your kids’ test scores? Or maybe transparent, non-defensive collegiality? Okay, good job on that one, now the followup: what kind of education policies are going to create the environment that fosters growth?)

I couldn't agree with that more.  Not because I think I'm a great teacher, but because I think I'm still making and learning from my mistakes. He also linked to another criticism of the film where the main complaint was the confusion on what it means to create an environment where learning happens in a classroom.

Here's a snarky comic strip on what to do to encourage students to read their textbooks. I agree with the premise (that reading the textbook is important) but I'm not sure I completely agree with the message.

Are we teaching students to think like scientists? (Preprint)

Bill Nye talks to Popular Mechanics about teaching evolution in schools, but I was struck by this:

So we want to excite a new generation of kids—every generation—about the passion, beauty and joy—the PB&J—of science.

Passion, beauty and joy are often forgotten in teaching science.  I suppose I'm guilty of it many times, too. Plus, cool acronym!

Here's a guide to what seminar speakers are really saying that was recently posted over at Science. I'm really thrilled that the colloquium speakers we get in our department are usually really good and interesting to listen to.

A well-known astronomy textbook author (and his wife? Not sure.) had a jokey letter to the editor published in the New York Times. Thankfully, it was really brief.

There's an article in last month's American Journal of Physics that explores what was discussed in over 300 conversations students had while doing clicker questions in an intro astronomy class.  I haven't (yet) read that article, but Stephanie Chasteen at The Active Class had a great summary of the article.  Makes me think about what I could be doing better with the clickers.

And the last link for today comes from the president of the National Council of Teachers of Mathematics who wrote an article with the provocative title: "Endless Algebra - the Deadly Pathway from High School Mathematics to College Mathematics".

Cat fight!

Cats gotta get the claws out sometimes. (Okay, every night.)

More snow

I thought this was lake effect snow, but then I got home and it was snowing there, too.

Macro Photography First Attempt

I went back to attempting the macrophotography project I had tried starting last Thursday. I realized the problem I was having was that I had been trying to figure out how to mount my camera on the micrometer stage, when I should be mounting my subject on the stage.

For a first shot, I wanted something simple, with lots of texture and a bit of color. Last night we popped some popcorn to have with a movie, so I grabbed a left-over piece and put it on the stage. Here's a shot of the popcorn that I got when it first came into focus. Notice that the bottom of the kernel is more in focus than the top.

With the stage I can move the kernel by tiny steps and bring it into the focal plane of the camera. The next shot is an image from the middle of the sequence of images that I took. Over all, the focus is better than the first shot, but there are still places on the kernel that aren't quite in focus.

I found a piece of software that I'm trying out which aligns and stacks all the images in a sequence to make the entire subject come into focus. I'm pleased with the result for my first try, but I think I overdid the color correction. Something weird happened with the black background which makes it look more grainy and less black.

Analysis of the "Big Bang Theory"

When I was in grad school, I used to ask my lawyer and doctor friends and relatives what it was like for them to watch shows like "The Practice" and "ER" because I was fairly sure that no one would ever produce a TV show about physicists.

Boy, was I wrong.

What kills me is not so much that the "Big Bang Theory" exists. I've long gotten over that. It's the in-depth analysis that physicists and physics educators go through to defend or detract from the show.

Personally, I just enjoy being wrong about my idea of what could make it on TV. As a physicist, I long ago learned to get used to being wrong.

Gedanken experiment: Levitate a physics sitcom?
By Steve CorneliussenCould scientists help the cause of science by helping CBS raise its physics situation comedy The Big Bang Theory from the level of Gomer Pyle, USMC to the level of MASH?
Might CBS let physicists help elevate BBT from the level of Seinfeld, a hilarious show about nothing, to the level of All in the Family, a hilarious show about society's profoundest issues?
During the early Vietnam years, CBS's Gomer Pyle portrayed a cheerful country-boy Marine and his irascible sergeant at a peaceful stateside base. The sitcom ignored Vietnam. Slightly later, CBS's MASH engaged war's horrors, but still provoked laughter, by imagining Marx-brothers-like situations at a ragtag mobile US Army surgical hospital near the Korean War battle front.

via Points of View by Physics Today on 1/18/11

Aborted plan

I was going to try some macro photography tonight, but I couldn't get the camera mounted to the stage with the micrometer travel control on it. I'll have to try fixing that soon.

Shy cat

It's pretty sad when this is the best photo I can get of one of the cats.

P.R. campaign for the classroom?

I came across the following post by Robert Talbert:

The inverted classroom and student self-image | Casting Out Nines

It's interesting stuff. I experimented a bit with using videos last year. Actually, I used all videos in Fall 2009 and no lecturing in the intro physics class I taught. I think there was a large chunk that didn't buy into the system. I kept using my system last winter, but I abandoned that approach last Fall. This quarter, I've reintroduced the videos, but I'm using more of a hybrid approach to class: videos posted before class starts and some mini-lectures during class.

What sticks out with me from Robert's post was the following:

"Let’s just say that you had better not use the inverted classroom model if you aren’t prepared to put out a constant P.R. effort to convince students of the positive benefits of the model and constantly to assuage student concerns."

He may be on to something here. Last Winter quarter I posted a video to the class website of Eric Mazur explaining his peer instruction method to other physics instructors. I told the class they should check it out if they would like to know more about why our class works the way it does. Exactly one student watched even a part of the video. This year, I've posted a few links to the website, but I'm not sure how many students have checked it out.

I'm agreeing with Robert on his message about the "P.R. effort" but I'm not sure about the best way to go about it.

"Spot of Color"

As a part of my Mostly365 challenge, I want to periodically complete some of the weekly assignments that some photography/gadget/news websites often have.

This is my entry for the "Spot of Color" assignment from Digital Photography School assignment. I set up some beads on the cabinets in the basement and played with my flash until I got something I liked.

I've been trying to learn to control the focus on my camera so that I can play with the depth of field a bit. I'm not 100% satisfied with how this came out, but I'm getting better. Plus, I used a tripod for the camera, which is something I'm usually too lazy to set up.

It was good while it lasted

Farewell, 2010 Bears. We hardly knew how good you were until you made it into the playoffs.

Floppy!!!

Today's photo is not a photo I took today, or a photo I took at all. Although, it is a photo I've been trying to photoshop a bit to improve the contrast, if at all possible. I'm not sure if there's any hope for that. Maybe if I had the negative of it.

Anyway, the photo is of me and a pair of characters which will be INSTANTLY recognizable to anyone who grew up in Iowa in the 70's and 80's. Duane Ellet and Floppy were icons to kids of all ages in Iowa when I was growing up. Getting to meet Floppy and tell him a joke was absolutely the highlight of a whole year. I got to meet Floppy twice: once at the State Fair and another time at a town festival. This photo is from the town festival. There was another time that I toured the WHO TV studio's for a school field trip, but Floppy was not there when we went on the Floppy Show set.

If you miss Floppy (like all Iowans my age do) you can see some clips which have been posted on YouTube.

Lost hours

Tonight I played a "quick" game of Civilization. Only 3 hours of my life were lost. I think this should hold me for the next few weeks.

Great mail day!

My two subscriptions arrived on the same day. :)

Cat-proofing

This is what our living room has looked like for the past three weeks. Renae put tape on the sides of the couch, ottoman, and all the dining room chairs. She also covered all the couch and ottoman with towels and blankets. So far, the cats have been pretty good about not scratching the exposed parts of the furniture. We're planning to slowly remove the towels and tape over the next few weeks. Since they have plenty of scratching posts we're crossing our fingers that they will leave the furniture alone.

Before and After

My small workshop in the basement has been pretty cluttered ever since we've moved in. It's still pretty cluttered, but today it got a little better.

Top Shelf

I get a new carving every year from my grandfather. Now that we have a house, I've started to display them on the top shelf in my room. I was trying to capture all of them as displayed in one shot, but it wasn't working out. What I did (re)learn about my camera was that turning down the flash power made getting a reasonable exposure easier.

Armitage

Looking eastward

Introduction to Arduino

New electronics workbench at Workshop 88

Steam

This is for a class discussion on latent heat of vaporization.

Cats near each other

Trying to use natural light. Not great results. But, hey, cats!

Cats - Naperville Jan 8 2011

Chicago River from Brown Line

Fullerton

Inbound Brown Line

Cat sleeps on litterbox box

This cat has multiple soft places to lounge which were purchased specifically for her. She prefers the cardboard the litter box came in.

First day of winter quarter

This desk won't stay clear for long.

First day of winter quarter

This desk won't stay clear for long.

Toy Camera effect

at Caribou for coffee

R wins 364-331

Renae won today. I got all the high value tiles, but she got the only bingo: refront.

R wins 364-331

Renae won today. I got all the high value tiles, but she got the only bingo: refront.

Running track lengths

Yesterday, Rhett at Dot Physics had a comment about last week's puzzler on Car Talk.  He had an alternate solution to the question about how a pair of people could walk side by side for an hour and cover different distances.  His solution was that they were walking on a circular track. (Read his solution for a full explanation.)

At the end of the post he said:

It doesn’t even have to be a circle – it can be just curved at the ends and straight in the middle. Of course in this case, the husband would have to slow down on the straight parts (or the wife would have to speed up) in order for them to stay side by side. But it could be done.

There was something about this that didn't seem right.  I remember the track I used to jog on had one lane that was 8 laps for a mile.  Let's use that as the lane for the husband in our example.

Here's the layout of the track:

Let's use Rhett's values for the inner and outer radii: 4 m and 5 m, respectively. If the outer track is an 1/8th of a mile, then how long are the straight sections?

1/8th of a mile is about 200 m. The circumference of the curved part of the outer track is d = 2×π×5 m = 31.4 m. So the length of each straight section for the outer track is 84.9 m. 

The circumference of the curved part for the inner track is d = 2×π×4 m = 25.1 m. But the length of the straight sections is the same.  So the total length of the inner track is 25.1 m + 2 × 84.9 m = 194.9 m.

The wife has to walk 33 laps to go 4 miles. If the husband and wife are walking side-by-side the whole way, he also walks 33 laps.  His lane was 1/8th of a mile, so he has gone 4 miles, plus an extra 1/8th.

I still like Dot Physics.

Results are in

Over the weekend, I was watching the Mythbusters episode which was testing the idiom "It's like taking candy from a baby."  The phrase is used to imply that something is as easy as, well, taking candy from a baby. But long ago, I realized that phrase makes no sense at all. Anyone who's every been around babies knows that if a baby wants something, then even if you can easily take it from them, what you're really going to have is whatever you took away plus an unhappy baby. If the something you are taking away is candy, then you're likely to get tears from the baby, too. So taking away candy from a baby is just mean.  I think that's a better representation of the idiom.  What said you on the poll?

Clearly, most people went with the traditional meaning.  The three "other" responses all included meanness or cruelty in some way.  Still, most people (3:1 from this non-scientific poll) seem to think it is easy and not that mean or cruel to take candy from a baby. 

What can you do with this?

I just wrote this up over at the home.drewsday blog, but the real reason for taking the photos was to use this in class next quarter. We start with thermodynamics; one of the first topics is thermal expansion and contraction.

I regularly read Dan Meyer's blog. He was (is?) a math teacher, but I'm consistently inspired by his ideas. One of his regular features is something he calls "What can you do with this?" [WCYDWT]. The idea is that he finds an example of something in the world which illustrates a math concept and brings it into the classroom.

When I saw the contraction of the vinyl siding on my house, I knew I could bring it into the class next quarter.  The question is: What can you do with it?

I want to present this to class, so I have to think of the questions that would be appropriate.  Usually, when I start a problem in class I make a list of everything I know and everything I don't know (or want to know).

What I know

• temperature outside today was 12° F. ( T_i )
• nominal length of the siding was 12 feet. ( L₀ )
• change of length (on one side) was 1/8 inch. ( ΔL )

What I don't know (would like to know)

• temperature when the siding was painted ( T_f )
• coefficient of linear expansion for the vinyl siding (α)

Relevant equation

• ΔL = αL₀ΔT

The problem is that I have two unknowns (ΔT and α).

I have no idea what the temperature was when the house was painted. I didn't even know the house existed when it was painted.  I suppose I could come up with a reasonable estimate, but realistically, there is a pretty wide range of temperatures to work with. Conservatively, I would guess that the painting could have been done when the siding was anywhere between 60° F and 90° F. That is a pretty wide range, so I'm not sure I want to try to estimate that and use it to find α.  So let's make the initial temperature something we want to find. 


This means that I need to figure out what the coefficient of linear expansion is for the siding. In class we discuss how the thermal expansion process is approximately linear over a certain range. I have no idea if the expansion of vinyl siding is linear or not.  I'm going to cross my fingers and assume it's linear-ish. 


With a bit of googling, I learned that vinyl siding is made of unplasticized polyvinyl chloride (uPVC). I also found the coefficient of linear expansion is listed as 50 ×10^-6 °C^-1 for PVC. I couldn't find uPVC thermal coefficient, but every listed coefficient I could find was close to this value. 


Using that thermal expansion coefficient, and solving for the initial temperature, I found that the initial temperature was 23.6° C, which is 74.5° F.  (Right in the middle of my estimated range, hmmm...)


I think that the value for the coefficient is reasonable.  I plan to work this example in class, then extend it by asking the class to calculate what the maximum expansion/contraction range would be for a 12' length of siding in Illinois weather.  I'll be looking for other ways to extend this. 


Side notes:

1. The units specified online for the coefficient of thermal expansion are often given as [L]/[L][T] (e.g. m/mK). Of course, the length units cancel and all that remains is inverse temperature units, which is how our textbook lists the units.
2. Coefficients of linear expansion for common materials varied quite a bit (sorry, not scientifically quantified) from one table to another. Surprisingly, the PVC coefficient seemed to always be within 2% of 50 ×10^-6 °C^-1.

I'm curious, so I'm setting up this poll...

Loudness and sound pressure levels

This morning the blogs and twitter feeds were linking all over the place to a passive amplifier for your iPhone. (See it here: Science & Sons OS v1.0)

The idea behind a passive amplifier is that it requires no electrical power to increase the amplitude of the sound wave which is presented to your ear. Just pop your iphone into the cradle and crank up the tunes. As long as the battery in the iphone is charged, you have amplified sound.

It sounded cool, so I checked it out. This is what caught my eye:

The Phonofone III is an elegantly designed passive amplifier crafted from ceramic and designed explicitly for iPhone. This clever device amplifies the volume emited from an iPhone internal speaker roughly 4x (approx. 60 decibels).

Wait. What? I get a 60 dB gain out of a device with no power?  Let's see if that passes the sanity check. I don't have an iphone, but I have heard the iphone playing audio from its internal speaker. Unamplified, at a moderate level, I would say the sound level observed from an ipod (at an average distance) is about the same as the sound level of a typical conversation.  Let's look at what the approximate sound level would be:

(I found this chart on OSHA's website. I assume the image is public domain, like most government images.)  From the chart you can see that conversation at 1 m is approximately 60 dB(A).  (The "A" means A-weighted, which is a weighting factor used to approximate the frequency response of the human ear.)   Let's be conservative and estimate the iphone unamplified level to be about 55 dB. That means that if I drop the iphone into the passive device the sound level should be 55 dB + 60 dB = 115 dB.  That's louder than the "Discotheque" rating in the chart (when/where was this chart generated?) which is also about 20 dB louder than a jackhammer at 15 meters.  Somehow I really doubt that the single horn + iphone is going to be able to compete with the speakers and amplifier of a dance club.

What about the other claim?  They say the sound will be about 4x louder.  Here's where the claim might hold some water. The basic idea of a horn is to provide better impedance matching  between the driver and the sound field and to control directivity of the sound radiation.  Assuming the horn is pointing at an observer, the sound level at the observers ears should be higher with the horn than without the horn.

What if their claim that using the horn causes a perceived 4x increase in loudness is true?  (Loudness is a perceptual quantity, where sound level - either sound pressure level or sound intensity level - is a measured quantity.)    Then, the only mistake that they made is equating a 4x increase in loudness with a 60 dB gain in sound level.  Here's a graph from a lab we do in my "Sound and Acoustics" class:

In this lab students hear a broadband tone which they assign an arbitrary loudness level rating. In this class, we all agreed to call the reference tone (relative sound level = 0 dB) a loudness level of 100.  Note, there are no units, since it's an arbitrary scale we made up for the lab. Then they hear several other tones where the level has been increased or decreased randomly and they are asked to rate the loudness of the tone with respect to the loudness of the reference tone.  

What I've plotted above is the class average of loudness level vs the actual relative sound level (in dB) for all trials.  Each sample was presented twice (not in sequential order) so the scatter is a sort of approximation to the uncertainty in the measurement.  The solid line represents a model that is what we would expect to see for a larger sample of the population.  For such a small class, the trend is pretty close to the "expected" behavior.

Note that a 4x increase in loudness, from either 25 to 100 or 100 to 400, corresponds to a relative gain in sound level of 20 dB, not 60 dB.

Under ideal testing circumstances, I could believe that a passive amplifier like the horn amp would give a 20 dB gain right in front of the horn.  But someone should have caught the 4x = 60 dB nonsense.

A side project...

Moving into our first house that we own, I thought it would be fun to try to document all the home-improvement (and maintenance) projects that we undertake.

Obviously, that means I must blog.

I'm announcing today the home.drewsday blog.  This is where I am documenting everything that we do in the new house.  Hope you like it!

Do what I do, not what I say

One of the things that I decided to do based on recent classes I've taught is to try to reinforce the importance of students reading the material before coming to class.  To that end, I decided to implement reading quizzes due every morning that class meets.  But I also want to have walked in my students shoes as much as possible, so I have decided to read every section that I've assigned to them and take notes like I want them to be doing.

It may seem obvious to do this for every class, and certainly when I've taught the upper level courses I read and re-read (and sometimes re-re-read) all the sections we cover.  But for introductory classes I find that to prepare I generally need only skim over the chapter to see what topics are being presented and in what order.  Then, I have enough to worry about with prepping demonstrations, clicker questions, homework problems, in-class tutorials and anything else I can think of to help cover the topic in an active-learning classroom to have a lot of time to actually read the whole chapter.  Starting early, though I hope to get far enough ahead that I can finish all the reading assignments before the end of the quarter.

The reading quizzes are going to have two questions which will be the same each time, and then one or two additional questions which will be unique for each quiz.  The questions which repeat are: "What are two important concepts that you learned from the reading?" and "What are two concepts from the reading which you struggled to understand?"

I plan to use these questions to guide my note-taking as I read the book.

School is starting soon

Yesterday, a bunch of colleges and schools started up for the year.  Our campus is on the quarter system, so I still have a few weeks left to prepare.  My browser has become cluttered up with education-related articles that I've been saving up to comment on, but I think I'll just dump them out here.

A conversation with Sean Carroll - in this NY Times interview from April, I was a little disappointed to read this response from Sean:

Whenever you say you’re a physicist, there’s a certain fraction of people who immediately go, “Oh, I hated physics in high school.” That’s because of the terrible influence of high school physics. Because of it, most people think physics is all about inclined planes and force-vector diagrams. One of the tragedies of our educational system is that we’ve taken this incredibly interesting subject — how the universe works — and made it boring.

I get what he's saying.  But I'm disappointed that he would paint all high school physics teachers with such a broad brush.  I believe that at some level, ALL physics teachers got into teaching physics because they found the subject to be terribly interesting.  What about giving them the tools and motivation to make their classes interesting?  What about structuring schools so that biology teachers are not teaching physics?  These are complex questions that the interview does not get into.

His response to the follow-up question which was about what he would do to improve physics education was a little better in spirit, but I think it's a little unrealistic to think that starting with the Big Bang and particle physics is something that will lead to better scientific literacy.

No grading, more learning - This was an article from "Inside Higher Ed" that I found via Metafilter. A professor at Duke dispensed completely with the traditional method of grading (where the professor assigns grades for work turned in) and chose to "crowdsource" the grading.   The class as a whole (I guess) assessed whether or not student work met the standards for the course.  The discussion on Metafilter rightly pointed out that many classes have cliques of students which professors may or may not be aware of.  I am impressed with how this professor was able to turn the focus of the class away from the grades and onto the learning.  I am, however, not deaf to the concerns raised by many of the commenters talking about this method.  I don't think this would work for my courses where almost everything we do is a "right-or-wrong" type of assignment.  Still, it was interesting and inspiring to see faculty get their students to focus on learning.

Does Professor Quality Matter? -  You should read this article (from the Journal of Political Economy) to get the whole story, but I'm just going to skip to the end and quote from the conclusion:

Our findings show that introductory calculus professors significantly affect student achievement in both the contemporaneous course being taught and the follow‐on related curriculum. However, these methodologies yield very different conclusions regarding which professors are measured as high quality, depending on the outcome of interest used. We find that less experienced and less qualified professors produce students who perform significantly better in the contemporaneous course being taught, whereas more experienced and highly qualified professors produce students who perform better in the follow‐on related curriculum.

I'm not sure how much to read into this as it relates to teaching physics, but it was a somewhat interesting article.

Cory Doctorow: What I do - Not education related, but if you're a nerd who follows Cory Doctorow, now you can do what he does.

You say up, I say yesterday - This is a great profile of a cognitive psychologist who has studied a fascinating topic of how language relates to thinking.  I was really blown away by these ideas. (Cog psy is ALMOST as cool as physics...)

Plan B: skip college - This NY Times piece doesn't say anything that hasn't already been said about whether or not college is the best economic choice for all people.  But, it is a good reminder that we (as a society) should constantly be questioning how ALL people can best be served by education at all levels.

What if College Tenure Dies? - A series of essays in the NY Times opinion section.  Really good, thought-provoking stuff here.

Tenure, RIP -  Closer to my heart (and life), though, was this article in the Chronicle of Higher Ed. about how the percent of tenure-track positions available across the country has shrunk dramatically in the past few decades.  I don't have the time to go fully into what I really think about this situation, but from a personal level, I would just be THRILLED if I could get offered some version of a permanent job.

This press release talking about a research project connecting a poem by Walt Whitman with a meteor shower caught my eye.  The research was cool, but I LOVED the interview with the student research assistant:

...get involved and be as active and connected with whatever department and professors they have. That's been the most beneficial thing to me. Once you start talking to your professors and meeting with your professors and they realize that you're a real human with a brain and you're interested and excited they'll do anything for you, and you'll do anything for them. With that, find someone -- it doesn't matter who it is or what department they're in -- find a professor and make a connection...Also, fear can get you down. That's why I didn't want to be a physics major [initially], because I was afraid I couldn't do it. Don't be afraid of boys, don't be afraid of professors -- once you get over that you can do anything.

The part about "Don't be afraid of boys" was because the question was about advice to give to other female physics majors.  But, I just found her overall attitude throughout the whole interview to be great. She has everything that every faculty member is looking for.

Hanny and the Mystery of the Voorweep - New graphic novel about the discovery of a weird astronomical object.

The Hot Young Teacher they Hired Instead - Along with the Tenure, RIP article, this sort of struck a personal nerve, simply by being about the hiring process in education and the pain that a teacher goes through.

Hot for the Wrong Teachers - This article from Slate is about 2 years old, but it was new to me.  This gets into some of the reforms that have been implemented at one school in NYC.  There is also a discussion of proposed ideas and what is and is not working currently.

Whew!  I had more stocked up than I had realized.

The usefullness of solution sets

I'm teaching a intensive introductory physics course this month. We cover a quarter of intro physics (algebra based) over a 3 week span. I have been handing out problem sets every day, which students work on every other day in recitation-style sessions.  None of the problems are graded, although the students are strongly encouraged to complete all the problems as part of studying for quizzes and exams.

I was a little surprised to learn that the instructor for the previous course (I'm teaching the middle course) provided complete solution sets to the students. It's not something I had planned to do. So on the first day of class, I was asked if there would be solutions provided.  I agreed to try posting solutions to the course Blackboard page.  Of course, this meant writing out solutions in addition to preparing for the next day. Since I had only written down the answers to the first set and needed to prepare the second set, I posted the answers to the first set and the solutions to half of the second set. By today, I was ready to post a full solution set to third set of problems.

I thought I was being generous.

Generally, I would not provide a solution set to a class.  I believe that students develop a false sense of security by relying on having solutions for all their problems.  Because, eventually I will give them an exam. And there will be no solutions for them. It's a bit like someone learning to ride a bike using training wheels.  You don't go from always using training wheels one day to entering a bike race the next day.

But a few of my students gave some clear reasons why they wanted full solutions.  The reasons ranged from "sometimes I don't know how to start the problem" to "if I'm getting the wrong answer, I can use them to check my work" and everything in between.  So, I'm going to try to post as many solutions as possible.  We'll see how it goes.

Popcorn soup!

Popcorn soup!

End of term clean-up.

Today I'm in my office to clean up and get ready for the summer term course I'll be teaching in July. I've got a stack of papers to go through, clear off my desk and dump in the shred bin. But, I've also got a collection of science news stories which have been cluttering up my browser. In the spirit of clean-up, here's a small link dump:

• PhD student in Canada is studying the psychology of earworms. (What's an earworm?)
• Another Canadian psychologist has examined how Rembrandt draws viewers into his paintings.
• An engineering student in England has adapted a bike to pump water in Guatemala.
• NASA's Mars Reconnaissance Orbiter flew over the Phoenix lander and may have imaged the damage to the lander, explaining why it never woke up after the Martian winter. 
• Infrared image of nebula from the WISE telescope looks like a pair of hearts situated next to each other in space.
• Want to go to Neptune and come back in 5 years?  It will only cost you $4 trillion. (More links at bottom of that page.)
• Possibly the most adorably unfortunate misspelling of hadron ever.  Let's hope this kid never loses his interest in science. 
• Something hit Jupiter last year, and amateur astronomers saw it first.
• In May, The Big Picture featured a round-up of really great images of Saturn and its moons.

I think that is all the links I've been saving up. You can always see my shared google reader links, even if you aren't following me.

Back to clearing the desk.

A tourist in our own town...

These are some ideas for places to visit in and around Chicago this summer when we have visitors and/or free time to go exploring.

If you are coming to visit us, or if you have any opinions on these places, let me know what you think of them.