September 04, 2013

The building that melted a Jaguar

Have you heard about the building in London that has been blamed for melting parts of a car by reflecting sunlight off of it?  It made the news today and was all over social media.

Image Credit: Matt Buck
The first thing I noticed was that the building is curved both horizontally and vertically. I thought it would be interesting to try modeling the building as a spherical mirror and see what I could estimate from this model. Is the building a part of a sphere? Probably not.  Is it close enough to use as a model? That's the fun of trying to figure it out.

I found some renderings of the building on its website. I decided to use the 32nd floor to use to estimate the focal length of the horizontally curved part because it looked to be the most curved of all the floor plans in the linked PDF. Here's a screenshot from that file:

You can see the full size image if you click the image. What I liked about the rendering of the floor was that there were dimensions given for the usable office space on the floor. What I didn't like was that there didn't seem to be enough information to directly estimate the radius of a circle defined by the arc of the side of the building. (Maybe I'm wrong about that. It could be an interesting geometry problem. Paging Dan Meyer...)  I also didn't like the part about the floor plans not being to scale. I chose to ignore that part. I did like that units were in meters. Because physics.

My plan is to draw a circle so the side of the building follows the edge of the circle. Then, I'll use the dimension given in the image to figure out the size of circle.  From that I can get the focal length of a spherical mirror of that size.

Here's what the circle looks like when I put it up to the side of the building:

The blue bar is a rectangle the size of the arrow 20.5 m long in the center of the lower part of the drawing. The red section is the fraction of the circle that I could get into this image.  Here's the zoomed out view:

That's a big circle.  Let's figure out how big.  The blue box when I drew it (in Inkscape, if you're curious) was 431 units (whatever a unit is) long. So the scale is 431 units / 20.5 m or roughly 21.0 units / m.

The circle has a diameter of 10640 units.  So the physical diameter of the circle would be 10640 units / 21.0 units / m = 507 m.

The focal length of a spherical mirror is half the radius of the sphere. So the focal length I estimate from this floor is about 127 m.

Looking up the the height of the building gives a value of 180 m, according to Wikipedia and Google, the sources of all knowledge. Figuring out the height of the 32nd floor is not straightforward, but I estimated it to be about 142 meters.

So if the building could somehow reflect the sunlight straight down (which is can't, and doesn't) then according to my rough estimates, the focal length wouldn't be at ground level.  This makes me believe the following could all be true:
  1. The light is reflected off of a lower floor. 
  2. The radius of curvature was underestimated.
  3. The floor height was overestimated.
  4. The ground level of the building is lower than where the car was sitting when it got melted.
  5. I made some other miscalculation.
I'm actually satisfied that I'm on the same order of magnitude for the focal length and the height of the building.  If the lower floors (say the 16th) have a larger radius (less curved) and are obviously closer to the ground, then the focal length could easily be longer than the distance from the windows to the ground. 

I think this is a neat way to apply some physics to an interesting news story. I have more to think about on this one. For now, I'll have to check and see what Rhett has to say about this building.

August 06, 2013

Video feedback to students

Our campus is going to be transitioning to a new Learning Management System (think Blackboard or Moodle) within the next year-ish. I volunteered to be on the LMS Task Force that is part of the process for selecting the new LMS. This summer I sat through four vendor demos showing off the incredible ways that their systems worked and how great they would be for our campus.

The four that we saw all do the same basic things.  There are some faculty on our campus who have specific needs for their courses like grading discussion forums, tying rubrics to certain types of assignments, various uses of calendars and other specific needs. Most of the systems actually seemed (on first glance) to handle most of these needs, although some seemed easier than others to set up and use.

What struck me as something new was that all four of the vendors featured the ability for instructors to provide video feedback to students via the LMS. I mean that it was a prominent part of each of the demos that all of the reps glowed about. I think that all of the video feedback implementations were via screencast, but I think most also weirdly included a recorded webcam session of the instructor talking to the student. I've been assigning students to do screencasts as homework for the past few years now, so I am no stranger to students and instructors communicating via screencast. Depending on the need, I've found it useful to post feedback as a screencast to students, but never my talking head.   

I asked some of the reps if the video feature worked for the students to post to the instructor or rest of the class.  It was clear that some of the LMSs had the ability, but none of them were intending for that use, which I found a bit disappointing.

So why are so many of these companies showcasing this feature? Are faculty using it? Do students like it?  Does it facilitate learning?  I feel that I have a pretty good pulse of the physics teaching community, and I don't see anyone using video communication as faculty-to-single-student transmission only.  Nor do I have a sense that instructors at my school want that either.  But, I could be missing a segment of teachers who find it to be really valuable.  If so, I'd be interested in hearing who is using it.

August 05, 2013

Does Khan Academy listen to content experts?

Christopher Danielson has an Open Letter to Sal Khan which has stirred up some discussion recently.  When I read his piece I was drawn to this part in the middle:
"Mr. Khan, you have a team of teacher advisors. If none of them can identify these gaps for you, you need to ask for help from the larger community (and then to reexamine your hiring practices)."
Out of all the criticisms of the Khan Academy, this is the one that upsets me the most. That KA in general, and Sal Khan personally, cannot find it in themselves to reach out to the education community to improve their offering indicates to me that they must not care about having high quality resources on their site, only that they care about having a high quantity of resources.

Over a year ago, I posted my critique of the stellar parallax videos.  In my critique I pointed out several (at least four) things that I thought were really good about the explanations of parallax.  But, I also pointed out some huge problems with the videos, including the incorrect depiction of the night sky showing East and West directions reversed (starting at about the 8:40 mark in my video). Apparently, Sal Khan does not know which way East and West go. None of the videos on parallax have been changed in the past year.

I realize that I'm just one guy, and maybe KA has no reason to listen to me. (Sal has yet to take me up on my offer to have him talk with us at the Global Physics department or an AAPT conference.) I have taught intro astronomy at least 20 times and we usually spend an hour or two of class time on parallax not including review time or out of class discussions that I have with students.  I have invested at least as much time prepping for teaching these classes, so I have at least 40 hours of experience in teaching this topic alone. I know there are teachers out there with even more experience than that, and I am constantly looking to learn from them. When I learn a better way to teach a topic, I alter my approach. Why isn't the same true for KA? 

I pointed out above that in my critique of the parallax videos I thought there were some pretty good things about them, including at least one part of the explanation that was unique (and accurate) and I hadn't seen anywhere else.  I'm pointing this out again in part because I'm not interested in rehashing any of the tired arguments that supporters of KA bring up over and over again.

Let's talk about how KA can engage with great educators at all levels so that we can all get better at what we are trying to do. Some of the KA staff do engage with others in discussions, but they sometimes miss the point.  In the Hacker News discussion that I linked to above Ben from KA says this:
"It's difficult for us to work through all of the submitted issues because most of them are from students who don't understand the problem or have made a mistake in their work, not real issues with the content. We always keep an eye on the number of issues per exercise, and we're lucky to have volunteers who read through the issues and surface the real issues."
To be fair, Ben is talking about responding to issues related to homework-like problems on KA.  But, his statement reveals the heart of the problem with what KA is trying to do: engaging learners in a meaningful way using algorithmic methods doesn't always (often?) work. I would argue this must be especially true for conceptual learning, which is the root of deep understanding in most topics. 

August 01, 2013

New tag in Evernote: Show-to-students

I have a new tag in Evernote  I called it Show-to-students. I have tagged everything clipped recently from the web that I want my students in the Fall (and semesters after) to read. These are articles, essays and blog posts which highlight ideas I think are important for the learning process. I'm sure I found all of these via my twitter stream, so I want to thank you all for posting them to twitter, whoever you were.

So far, I have five items to share with my classes.

The most recent one that I found is the excellent post on ConvergeDiverge about the teaching philosophy that Maxwell had. I think Heather has a great insight that we as instructors have a struggle with some (or many) of our students between how deeply they want to think about the topics we would like them to think about. As my comment (and Heather's reply) indicate, I think it could be helpful to address this issue at the start of the class as a part of setting the tone and expectations for the class early.

Another article that I'd like to share with my class is the article from Slate on the inability of students to effectively multitask. The article includes this nugget:
During the first meeting of his courses, Rosen makes a practice of calling on a student who is busy with his phone. “I ask him, ‘What was on the slide I just showed to the class?’ The student always pulls a blank,” Rosen reports. “Young people have a wildly inflated idea of how many things they can attend to at once, and this demonstration helps drive the point home: If you’re paying attention to your phone, you’re not paying attention to what’s going on in class.” 
I don't know if I could execute that move in class unless I've told the class to read this article in advance. I'd also consider using Patrick Len's excellent approach to cell phone / social media use in class: poll the class and use the class discussion to set the cell phone / social media policy.  But really, I just want students to be thinking about how much they can actually learn while they are trying to multitask.

When I looked at my tagged articles, there was a surprising pattern I had not expected: three of the five articles were about the role of failure in learning. I must have been channeling a certain skateboarding physicist when I was tagging these articles. "Failures, Mistakes and Other Learning Tools" was a blog post that sat in one of my browser tabs for MONTHS last year. I was really inspired by how this teacher handled his student's confrontation with failure for the first time. The blog post on Scientific American which told the story of Feynman's attitude toward being wrong in science should be mandatory reading for all future scientists. Then there is this incredibly honest piece on Slate by a math teacher on what it was like for him to have been "bad at math" and how that experience ultimately made him a better teacher. I'd like to connect that idea to the growth mindset that Dweck writes about in her book.

I saw a question on Quora that also connected failure with learning.  It was good, but I'm not sure if I'm going to add it to the list. I might just leave my students with Adam Savage's catch phrase: Failure is always an option.

July 31, 2013

Toothpick / matchstick lab idea

Since I am going to use the "Measure the value of pi" lab for introducing graphing, equation editors and potentially writing a lab report, I want to have a lab where the goals and the experimental procedure is developed by the students in the class from top to bottom as much as possible.  Here's my idea:

I plan to give students a taped box of matches or toothpicks with a random number of matchsticks or toothpicks in them. Alternatively, I could have a single full box that students could have with the ability to put as many or as few matchsticks or toothpicks in as they choose.  Hmmm….going to have to think about that one.

There will be only one rule: students cannot open any box until the lab is done and the report is written.

I'm going to ask students: What do you want to know about the box?  I want them to write their questions down before they say anything. Then I'll have them discuss in small groups with whiteboards.  Then we'll have a short all-class discussion of the questions they are interested in.

I am hoping that the groups will come up with at least "How many matchsticks (or toothpicks) are in my box?" But I would also be thrilled if they came up with questions like "What is the mass of a single matchstick (or toothpick)?" and "What is the mass of the box (and tape)?"  These are my goals for the lab, it will be interesting to see what the class comes up with. If needed, we can have a discussion which leads us to these goals.

I will have prepared ahead of time several identical boxes each with a unique number of matchsticks or toothpicks in them and marked on the box itself. I will try to use the same amount of tape on each box, so each box is as identical as possible.

This is the first lab where I will encourage the students determine the process by which they will meet the goals of the lab. I don't know if it's the best way to encourage this process, but it should be a good follow up to the pi lab.  I don't think there are many ways to find the mass of a single matchstick or toothpick, the mass of the box and the unknown number in the initial box, other than using a linear fit model, but I'll leave the students to figure that out.

I want to have students make predictions or guesses for the quantities they want to measure before doing the lab. I think it will be interesting to see how these guesses compare to the experimental data. We can have some discussions about orders of magnitude if there are wildly varying guesses.

Then we'll do the lab. I tried this myself and it went really quickly.  There's not much to do other than mass the boxes and record the data.

I want to make sure every student has a graph of the data and has used equation editor to express their best fit line equation.  If time permits, I want to have them start to write the lab report.

My worry with this lab is again that it is too easy.  I hope that by emphasizing the students' control of the goals and procedure it will hold their attention to the end of the lab.  Plus, if we finish early, I have an idea for the next lab to do.  :-)

July 30, 2013

First lab of the year - crawling before walking before running

There was a day last semester in the algebra based physics class (mechanics and thermo) towards the end of the semester when one of my students through up his hands and complained: "How am I supposed to know how to make a graph in Excel when you never taught us how?!"

On the one hand, my thoughts were that they had been writing and turning in lab reports all semester which were supposed to have had graphs on them, plus this being a college class I figured that either they would 1.) know how make a graph or 2.) ask me for help without getting frustrated.

On the other hand, my thought was the student had a point: I had not done anything with making graphs.  

Another shortcoming that many of the students I see have is never having used the equation editor in Word (or even having heard of TeX).

This Fall, I'm going to go back to one of my old favorite first labs and make it a learn to graph / introduction to equation editor / introduction to linear fits and the practice of writing a lab report exercise. 

The lab is a "Measurement of Pi" lab where students are given a bunch of circular objects and asked to experimentally determine pi. The past few times I've run this lab, I've used it more to introduce the idea that students should be able to design their own experimental techniques in lab to meet whatever goal I choose (or ideally, whatever goals the students choose.)  While I think this is an important lesson for intro physics (for engineers or not), I think I can de-emphasize the design part a bit if we use the lab to introduce some important techniques to be used throughout the lab.

So, here's my vision:
  1. Get students into groups. Each group gets a single circle but all circles will be of different size.
  2. Ask students to think of what quantities they could measure with the circles.  Have them whiteboard these ideas, then share with the rest of class.
  3. If no group comes up with value of pi for answer, ask if there is a quantity which is fundamental to all the circles, regardless of size.
  4. Ask groups to come up with a way of measuring pi. Have them whiteboard it and share with rest of class. 
  5. Have a discussion of the difference between experimental uncertainty and error as well as taking an average vs. creating a graph with linear fit.
  6. Each student makes a graph of the class data. We include error bars and a linear fit.
One of the advantages that I have at our college is using a "studio physics" approach where I have a minimum of 2-hour class meetings. (MWF are 2 hours each, TTh classes are 3 hours each: both a blessing and a curse.) Since I have long meeting times, I can piggyback lessons on top of each other. Plus, I get to walk around and help groups or individuals as needed.  Depending on how quickly we get through this activity, I would like students to start working on their lab report, too. Within the lab report, they should include the equation of best fit for the data by using the equation editor.

So there's a lot for students to digest here: graphs, best fit, uncertainty, equation editor, lab report writing.

How much class time can we devote to this?  I'm not going to spend more than a 2-hour block on this, especially since I want to do a lab where the students are more in charge of the design of the experimental procedure and analysis. (More on that idea soon!)

My fear is that we as a class will not manage the time appropriately on the first day.  I want to do FCI on the first day as well as breezing through the syllabus.  Then, if I hit them with this lab, well, it might be a lot.  On the other hand….the concept at it's core is really simple: we're going to make a graph of circumference vs diameter. So, maybe it won't be too bad.  As a backup, I will have the followup labs ready to go in case the class finishes really early.

July 03, 2013

Back in the (scientific) python business!

The above five lines of python represent the accomplishment of a (small) summer goal of mine: to have one cohesive python install with all of my favorite python packages for writing code for physics classes and research.

I don't know what happened earlier this year, but I had b0rked up my python install on my school laptop. I have a Macbook Pro, and was running into all sorts of problems: 32 bit vs. 64 bit, which install of python to use and whether or not I could use matplotlib and vpython at the same time.

What I ended up with was two installs of python: one that could use vpython and one that could use matplotlib, but never the two at the same time.

As you can see in the screenshot, I have everything working now with the excellent enthought distribution of python. What I learned today was that ALL  the packages in the vpython dmg file are required to run vpython. I don't remember my original thought process which led me to believe I didn't need the other packages, but I did. Also, I learned today that you can't always (simply) run vpython calls from the python shell, unless you limit the rate of displaying frames by putting rate() inside a loop.  More on that later, maybe.

I know the above packages have significant overlap (scipy extends numpy, pylab has matplotlib, etc.) but I've used each of those in various forms, so I wanted to be able to call any of them without having to THINK about it.  Done.

Okay, so if you made it this far into this post, you deserve a reward. How about 8 tutorials on scientific python programming? My favorites are the SciPy tutorial and the excellent matplotlib tutorial.

June 26, 2013

School year 2012-13 reflections

I had my annual review with my dean yesterday.  It went well, and although I don't have much to say about the review specifically, it was a time to reflect on things that went well and not so well in class this past year.

What I've come up with are things that I'm going to try in order to build on what has been going well and correct things that are not going so well:

  1. I'm going to completely change how I assign what I call "Reading Reviews". This is probably going to be my biggest change next year, and I plan to have a separate post on this topic soon.
  2. Lab report first drafts are going to be due the next class period we meet after the lab has been completed. Part of the point of a science course should be to model good scientific processes. I am terrible at quickly writing up scientific work that I do. But, if I want my students to start forming good habits, then we need them to write up what they do in lab as quickly as possible. That way there is less time for the memory of what was done in lab to fade. I will continue to use the policy of allowing as many rewrites as needed to get full credit on the lab.

    I saw that Joss posted about his concerns about lab report revisions on twitter today:
    That's a concern I have, too, but ultimately the responsibility is on the student to meet the expectations put forth in the syllabus.
  3. I give a lot of short quizzes the first part of the semester, hopefully to encourage preparation for exams. I am planning to grade the quizzes in class as soon as they are done. We use a studio physics classroom, which makes for long class periods (at least 2 hours), and since I see my role as a facilitator of the learning environment rather than a lecturer, I will need to have mostly self-directed tasks for the class to work on for the 20ish minutes it will take to score all the quizzes.  My goal is to have the immediate feedback encourage the students to come to class better prepared for quizzes and exams. Even though I'm not using standards-based grading specifically, I am striving towards keeping the spirit of SBG. (Excellent post by Frank Noschese.)
  4. Based on what I learned at the New Faculty Experience, I will be trying to make more frequent reflections.  I started doing this late in the year using Evernote.  Part of my problem with doing it regularly was that I had a tight schedule last semester. In the Fall I won't have that issue.
If I could identify a few things that went really well this year, I would say that in the Spring term especially, I used a lot of the TIPERs activities with whiteboards fairly effectively.  I do think I need to better introduce how the class needs to share their whiteboard work with each other.  Also, although we were able to do more labs (and more effectively, I think) I have some plans to better introduce some of the skills I expect them to use throughout the term.

I'm really happy with how the last year turned out.  I am looking forward to the Fall, but really happy to have the Summer to prepare for it.

June 24, 2013

Musical Acoustics Research Library online!

If you're interested in the field of musical acoustics you'll definitely want to check out this resource from Stanford: the Musical Acoustics Research Library.

I found out about MARL when I received an email with this press release. The collection is broken up into four parts: a collection of material from the Catgut Acoustical Society, and collections of materials from three well-known acousticians.

Much of the material has been digitized, allowing anyone to peruse the correspondence between colleagues, drafts of articles and the ephemera contained in the collection.

According to this post, the collection is completely digitized, but there seems to be some parts which are not available online.  I'm not sure if that's due to copyright, or if there are plans to post the rest of the collection online in the future. In any case, what is online right now is a great resource for musical acoustics and also a neat look into how scientists collaborated with each other from the 1960s through the late 1980s and 1990s.
the John W. Coltman Collection, the Arthur H. Benade Collection, and the John Backus Collection. - See more at:
the John W. Coltman Collection, the Arthur H. Benade Collection, and the John Backus Collection. - See more at:
the John W. Coltman Collection, the Arthur H. Benade Collection, and the John Backus Collection. - See more at:
the John W. Coltman Collection, the Arthur H. Benade Collection, and the John Backus Collection. - See more at:
the John W. Coltman Collection, the Arthur H. Benade Collection, and the John Backus Collection. - See more at:
the John W. Coltman Collection, the Arthur H. Benade Collection, and the John Backus Collection. - See more at:
the John W. Coltman Collection, the Arthur H. Benade Collection, and the John Backus Collection. - See more at:
the John W. Coltman Collection, the Arthur H. Benade Collection, and the John Backus Collection. - See more at:
the John W. Coltman Collection, the Arthur H. Benade Collection, and the John Backus Collection. - See more at:
the John W. Coltman Collection, the Arthur H. Benade Collection, and the John Backus Collection. - See more at:

June 14, 2013

Github for science: anyone played with these yet?

If you've written any amount of code beyond "Hello, world" you are probably familiar with the idea of version control systems. The idea is simple: you use a piece of software to keep track of changes that you've made to your code. If you are working on a complex project involving multiple people, using a VCS is likely the only way to efficiently manage the project.

If you're working on a project with a collaborator, there is no need to be in the same location as each other if you are both able to access the shared space where your files can be indexed by the VCS.  Most VCS make it trivial to work with others via cloud-based services.

One VCS that is popular is called git.  There is a web service called GitHub where coders who use git can check-in their code and collaborate with others. And, although there are people and organizations starting to use GitHub for non-software projects, there are GitHub-like clones popping up for specialized fields.

Two in particular have caught my eye for scientific research projects: SciGit and Banyan. Both of these sites are pretty new, and they both seem to have roughly the same idea: a service for scientists to collaborate on projects with version control without having to learn a lot about git itself.

I'm interested to know if anyone out there has looked at these sites or tried them out.

June 12, 2013

Science Hall, Goshen College - 1947-53

This photo was taken sometime between 1947 and 1953, according to the information on flickr.

How many physics (and/or science) classrooms look the same 60 years later?

At least we don't use the giant built-in power supplies anymore.

Via Flickr:
Caption: April, 1948. Goshen, Indiana. Interior scene in Physics Lab in Science Hall, Goshen College.

Citation: Mennonite Community Photograph Collection, 1947-1953. Goshen College. HM4-134 Box 2 Photo 301-9. Mennonite Church USA Archives - Goshen. Goshen, Indiana.

May 22, 2013

World's silliest arduino-based electronic musical instrument

This is the world's silliest arduino-based electronic musical instrument. It is a mashup of the "Melody" tutorial and the "Button" tutorial.  The code I modified (see below) strips out the part where the tune is actually played and instead plays a single note when each button is pressed.

/* Melody
 * (cleft) 2005 D. Cuartielles for K3
 * This example uses a piezo speaker to play melodies.  It sends
 * a square wave of the appropriate frequency to the piezo, generating
 * the corresponding tone.
 * The calculation of the tones is made following the mathematical
 * operation:
 *       timeHigh = period / 2 = 1 / (2 * toneFrequency)
 * where the different tones are described as in the table:
 * note  frequency  period  timeHigh
 * c          261 Hz          3830  1915  
 * d          294 Hz          3400  1700  
 * e          329 Hz          3038  1519  
 * f          349 Hz          2864  1432  
 * g          392 Hz          2550  1275  
 * a          440 Hz          2272  1136  
 * b          493 Hz          2028 1014 
 * C         523 Hz         1912  956
int speakerPin = 9;
int button1 = 3;
int button2 = 4;
int button3 = 5;

int val1 = 0;
int val2 = 0;
int val3 = 0;

int length = 15; // the number of notes
char notes[] = "ccggaagffeeddc "; // a space represents a rest
int beats[] = { 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 2, 4 };
int tempo = 300;

void playTone(int tone, int duration) {
  for (long i = 0; i < duration * 1000L; i += tone * 2) {
    digitalWrite(speakerPin, HIGH);
    digitalWrite(speakerPin, LOW);

void playNote(char note, int duration) {
  char names[] = { 'c', 'd', 'e', 'f', 'g', 'a', 'b', 'C' };
  int tones[] = { 1915, 1700, 1519, 1432, 1275, 1136, 1014, 956 };
  // play the tone corresponding to the note name
  for (int i = 0; i < 8; i++) {
    if (names[i] == note) {
      playTone(tones[i], duration);

void setup() {
  pinMode(speakerPin, OUTPUT);
  pinMode(button1, INPUT);
  pinMode(button2, INPUT);
  pinMode(button3, INPUT);

void loop() {
  val1 = digitalRead(button1);
  val2 = digitalRead(button2);
  val3 = digitalRead(button3);
    if (val1 == LOW) {
      playNote('c', 1 * tempo);
//    } else {
//      playNote(notes[i], beats[i] * tempo);
if (val2 == LOW) {
      playNote('e', 1 * tempo);
    if (val3 == LOW) {
      playNote('g', 1 * tempo);  


Hoop jumping

INCIDENTAL COMICS: Message to a Graduate
Image credit: Grant Snider, Incidental Comics

By the end of high school, all I could see was the hoop jumping. I was so sick of it: every class was predetermined for me with only my extracurriculars to numb the boredom of the required classes. I looked forward to college knowing that while I would have to take general education classes, at least I would have options to choose from.

By the end of college, I saw that while the hoops were fewer and further between, I still detested them. I put off some general education classes until the last year I was in school.  I looked forward to going to grad school where there would be no hoops to jump through.

By the end of grad school, I realized that I was wrong about the hoops.  They were still there, they were just disguised. I grudgingly jumped through them and looked forward to getting out of grad school so I could be free of the hoops.

By now I've come to understand that the hoops never truly go away.  But what this comic says to me is that I can choose my own goals which are interesting to me.  That makes all the difference in the world.

(Thanks to @rjallain for pointing the comic out to me on twitter.)

May 08, 2013

New rules for screencast assignments

I tend to really hate rules in the classes I teach. I like the formats to be free flowing so that students are empowered to learn in their own way and in their own style.

I like screencasts as assessments, especially when I'm able to get them watched and responded to rapidly as intended. But anyone who makes blanket statements about students today being "digital natives" who grew up online creating and sharing content have not been in the same classrooms I've been in.

For next year I have some new rules for submitting screencasts:

1.) I will only accept URLs as screencast submissions.  I don't want a file as an attachment to an email in whatever crazy format came out of the camera. I don't want an audio file with a snapshot of the work done. I don't want a thumbdrive with each screencast file sized over 300 MB. I want a link to your screencast which is on youtube,, vimeo or similar.

2.) All students will be shown this Public Service Announcement on the first day. If I can't see the work done on the page while I'm in full screen mode, then what is the point of getting the visuals? Not that it is much better sometimes when the camera is held close to the page. My head hurts after watching videos where less than half a page of work is shown in video and so the camera is constantly panning back and forth.  The same goes for videos sent to me in landscape orientation but with the page rotated...or upside down.  Students will be told to watch their videos before sending me the link.

3.) All phones must have notifications turned off while recording screencasts.  I'm listening to screencasts when the volume explodes with some random buzzing and I jump out of my skin. It is five freaking minutes that the text messages, facebook updates, tweets, emails, phone calls and instagrams can just be shut down.

Most of the complaints I have are about screencasts done using cell phone cameras.  I don't mind the use of the cell phone camera, it just seems more prone to the problem videos that I get.

March 30, 2013

On gender stereotypes, rocket science and the f-bomb

The above was retweeted by someone I follow this afternoon, and I was interested enough to follow the link to see what the minor uproar was about.

Reading the obituary, I learned a great deal about the contributions to engineering of rocket systems used in satellites and space missions made by an engineer who happened to be a woman. As so often happens when I read obituaries, I was a little sad that I did not know more about Yvonne Brill's accomplishments during her lifetime, but I do feel enriched by having learned something about her life and work.

Of course, the reason that the obituary was pointed out by Ed Yong was because it leads (lede? I'm not a journalist.) off with a stereotype of a women as a cook and mother. I take Yong's outrage to be that because this was first in the article, it must be assumed that we are to think that Brill was foremost a mother and wife and secondarily, therefore lesser, a scientist or engineer.

When people I respect link to other people that I don't follow on twitter, I do want to take them seriously. On the other hand, I have hesitations about engaging with people dropping f-bombs. The chance that the issue raised is too likely to be emotionally charged that I have a hard time judging rationally the actual content of the article.  In this case, I had to reread the article three times so that I felt I could honestly evaluate the problems with this article.

Here's the introduction to the obituary:
She made a mean beef stroganoff, followed her husband from job to job and took eight years off from work to raise three children. “The world’s best mom,” her son Matthew said. 
But Yvonne Brill, who died on Wednesday at 88 in Princeton, N.J., was also a brilliant rocket scientist, who in the early 1970s invented a propulsion system to help keep communications satellites from slipping out of their orbits.
Is there a way that it could have been written to be less offensive?  Let's try this:
She made a mean beef stroganoff, followed her husband from job to job and took eight years off from work to raise three children. “The world’s best mom,” her son Matthew said.   
Yvonne Brill, who died on Wednesday at 88 in Princeton, N.J., was a brilliant rocket scientist, who in the early 1970s invented a propulsion system to help keep communications satellites from slipping out of their orbits. 
That's better.  There's no need to include words like "but" and "also" when we're talking about people's career versus personal life.  The distinction should be obvious to any reader.

Can we make any other improvements?  What if the order of the first two paragraphs were switched?
Yvonne Brill, who died on Wednesday at 88 in Princeton, N.J., was a brilliant rocket scientist, who in the early 1970s invented a propulsion system to help keep communications satellites from slipping out of their orbits 
She made a mean beef stroganoff, followed her husband from job to job and took eight years off from work to raise three children. “The world’s best mom,” her son Matthew said.
I personally feel the argument that starting with the cooking and family life details is implicitly misogynistic to be a little weak. I had to read the article multiple times to make sure I wasn't missing something more than the opening paragraphs. By my count, 16 of the 22 paragraphs were about Brill's work, including being a woman in a male-dominated field. Is she not also entitled to be remembered for what she was like away from the office? By simply reversing the order of the two first paragraphs, the implicit framing of Brill as woman first, scientist second is removed, no doubt.  For me, that's enough to justify a claim that the obituary could have been better written.

But, can we take the outrage down a few notches?  Reading through the conversation following Yong's tweet, it seems that there is a "you're either with us, or you're against us" mentality. No doubt, there are some who just don't get what the outrage is about. Are we trying to raise awareness about how profiles of scientists can be framed in potentially harmful ways, or are we just looking to have outrage for the sake of outrage?

For me, I learned about the life work of a person I had never heard of, and I am grateful I now know a bit about her. But, it was also a reminder why I'm skeptical of emotionally charged tweets. In this case, I clicked through, and was please to learn about Brill. I might have just as easily decided to skip the article because of the language in Yong's tweet.  Frustrated or not with gender stereotypes, I don't believe that the science community is necessarily always better off with outrage as the default reaction.

March 04, 2013

Why I don't like the "Doppler Rocket"

It's time for me to rethink how we look at the Doppler effect in class.

When I'm working with a class on the physics of sound, whether it is a general physics class or a physics of music class, the Doppler effect is always one of the topics in whatever textbook we are using. Time permitting, we will look at the Doppler effect.  I think it's an interesting topic, and it certainly has important and useful applications in other fields of science: astronomy, medicine, weather, etc.

What I can't stand, though, is the terrible quality of the standard acoustic Doppler effect demos. I'm talking about the demonstrations where you take a sound source and tie a string to it, then whirl the string around your head with the sound source making a circle around you. The class is supposed to hear the change in pitch alternating between getting higher (while the source is moving toward them) and going lower (while moving away from them).

Unfortunately, the demo often has two major flaws with it:

1.) The change is pitch is often within the just noticeable difference (jnd) for non-ear trained musicians.


b.) The change in pitches is almost always overwhelmed by the observation of the relative change in AMPLITUDE.  As the source moves away from the class, it seems to be less loud, and louder as it is approaching the class.

The situation is not much better when the demo is using a "Doppler Rocket" or "Doppler Ball" where a sound source is embedded in a soft ball then thrown or slid along a guide string across the room.  While it is usually the case that the frequency change can be more noticeable with these demos, since the speed of the ball can be high enough to make the frequency be outside the average jnd, my experience has been that the change in amplitude is even more dramatic with the Doppler Rockets.

What to do?  For me, it's interesting. I mean, one of the main ideas in science is that we only want to test one thing at a time. But in this experiment, we seemingly have two inextricably linked quantities that are changing.

I don't have a real good answer for what I want to do to get around these conceptual challenges. I've tried an Interactive Lecture Demo style presentation on the Doppler effect without the success I was hoping for.  I may try that approach again, but I'm sort of leaning towards making the Doppler effect a lab activity where students have to confront the two aspects of the experiment (frequency and amplitude) and tease them out separately.  I'm not sure if that will work at the introductory level, but I'm willing to try.

March 02, 2013

Weekend book review: The Radioactive Boy Scout

One of the first magazine articles I ever remember reading on the internet was the story of a teenager who wanted to build a nuclear reactor at his home. This was probably in 1998, during the thick of my time in college majoring in physics.  That time, as I recall, was before it was common to have magazine articles online. But Harpers Magazine was forward thinking, and the article was linked to from several nerdy websites that I read daily back then.

I learned about the concept of a breeder reactor, I learned that smoke detectors often used radioactive sources for their operation, and I learned that I wanted to know more about this story.  I was happy to hear that the author of the book had written a full-length book on the topic.

It took me awhile, but I finally got around to reading the book "The Radioactive Boy Scout" a few years ago.  I was not disappointed in the fleshing out of the story, although I was also not surprised that in parts of the book it felt like it was being padded to fill space.

The book was definitely a quick read, and it was worth going back to after years of first hearing the story. 

The Radioactive Boy Scout: The Frightening True Story of a Whiz Kid and His Homemade Nuclear ReactorThe Radioactive Boy Scout: The Frightening True Story of a Whiz Kid and His Homemade Nuclear Reactor by Ken Silverstein
My rating: 4 of 5 stars

View all my reviews

March 01, 2013

Is Marcus right? (Physics of the Funnies)


Here's another comic that I think could be used to spark discussion in a physics class. Some questions that I would want to elicit from my class:

How long is Marcus watching Jason fall?
What forces are on Jason?
How would we characterize Jason's motion? (constant velocity vs. accelerating)

Then, to go Mythbuster's style on the discussion: is the scenario plausible? Of course, it is a comic strip; it does not have to be plausible.  But, if it is not plausible, what conditions would have to be met to get the motion depicted in the comic?

Finally (for this post, at least): is Marcus right in what he says at the end?  Would using less helium make a difference?

February 28, 2013

Ancient astronomy

The above image is the first slide that I use to introduce the topic of ancient astronomy in my introductory astronomy course. It's something I put together a few years ago, and although I still sort of like it, I have a hard time remembering exactly what all the thumbnails are supposed to be representing.  As best as I can remember, the points I was trying to illustrate when I first put this slide together were:

1.) Many cultures around the world had at least rudimentary knowledge of the night sky, and in many cases had knowledge of astronomical alignments related to the calendar.

2.) We don't have time in class to talk about all of the interesting things that these cultures knew about. There is a LOT of interesting material that we could go into, but in the interest of getting to some modern astronomy topics, we have to pick and choose some ancient astronomy topics and leave the rest mostly untouched.  That's not to say that non-Western cultures did not know about or explore the cosmos.

From left to right in the above image, then:

The pyramid is El Castillo, also known as the Temple of Kukulkan located at Chichen Itza (not Chicken Pizza, as my tour guide told me when I went there a few years ago).  The temple is aligned such that on the equinoxes the sun casts a shadow over the steps of the pyramids which connects to the heads of serpents carved into the base of the steps. It's a pretty neat effect, and shows the Mesoamericans knew when the equinox would arrive and how to align the structure to accomplish the effect.  The Chichen Itza site also has what is thought to be an astronomical observatory on it. The tour I went on did not allow for a very close approach to the building, nor did the guide we have know much about that particular structure.

The middle image is (I THINK) a photo of the ruins of Babylon.  I do not believe that the particular image had any astronomical significance. Rather, I think I was trying to point out that many cultures in the middle east (Babylonians, Sumerians, Assyrians) at least attempted to understand the night sky. Clearly, I am not a historian, anthropologist, or archeology expert. I would like to know more about the ancient astronomical knowledge of the middle east.

On the right is a photo of a an armillary sphere at the Purple Mountain Observatory in China. This type of sphere was used by ancient astronomers to measure the position of stars in the night sky. What is not clear from the article that I linked to is whether or not the pictured instrument is an original or a replica.  I seem to recall that the armillary sphere at the Purple Mountain Observatory is actually a replica of the ancient instrument. I think that the replica is itself relatively old, but again, it's not clear from the page I linked to.

Maybe in the future I can dig up the original references I was using to piece together this slide.  For now, I'm happy with what I have.

February 27, 2013

Browser clutter - February 2013 edition

This is where I dump some links that I've had in my browser tabs for awhile.  I don't want to forget them, but I don't have a better place to put them.

Music inspired by astronomy - from the Astronomy Education Review.  I wish the pieces in the article had better links.

Inertia games - We have some REALLY OLD computers at school that we keep mostly to do this for algebra based physics courses.  If I could find a port of this to some new platform it might free up some space and time in the labs. (Alternative link)

Love2D - an open framework for making games.  Maybe could write an Inertia Games clone in this.

Over the winter break I was able to go to the national AAPT meeting and give a talk on the history of modal analysis.  I titled the talk something like "From Chladni to the present, a history of modal analysis".  In preparing for the talk, I was surprised to learn about a bunch of pseudoscience that has taken from the work done by legitimate scientists and applied to all sorts of nonsense.  At the risk of increasing traffic to their sites, I will point out some of the more laughable crap that I came across:

Harmonic Resonance Theory - weird.

Cymatics history - history of, uh, cymatics (whatever that is) "research".

"How the leopard gets its spots" - In 1988 Scientific American published this article, which may or may not be good science. All I know is that the inference that the modal analysis of a metal plate cut in the rough shape of a animal skin is related to how the patterns of spots appear in the animal's fur is just bizarre to me.  (Google search)


Making cloud chambers - I've tried this a number of times, and they never quite work for me.  :(

More links later!

February 26, 2013

What can you tell about this scene?

I'm going back into the archives for this comic strip. This is a "Rose is Rose" strip from January 22nd, 2007.  I like this strip not because there is anything wrong with the astronomy (as far as I can tell), but because I can use this comic strip to ask the following questions:

What time does the couple go out for a walk?

What direction are they walking?

More generally, depending on when I use this strip in class, I could ask: What can you tell about this scene?  Then, the class can discuss things like the time of day and/or the direction the characters are facing.

February 25, 2013

What, if anything, is wrong with this comic?

Image Credit: Creators Syndicate, originally published 5-30-2005
This is the first few panels from a Sunday "Wizard of Id" comic from several years ago.  I would like to use it as a "What, if anything, is wrong with this picture?" challenge for my astronomy students.

So: what, if anything, do you think is wrong with this comic?

February 23, 2013

A few blogs you're probably not reading, but should be

A few weeks ago, Brian Frank posted a link on twitter to a blog about PER that he thought many physics teachers might not know about. I wanted to point out some people that I really like reading that I suspect many people don't know about, either.

Patrick Len posts a lot of questions from his physics and astronomy classes and quizzes over on his blog. Some of the questions are peer-instruction style questions for use in class, but recently he's been posting questions related to current events in astronomy. He also posts a lot of useful materials for activities and demos that can be done in class.

Matthew Francis is a physicist now working as a science writer. I came across his blog, Galileo's Pendulum, when I was tracking down some information about a local science landmark. He writes about a wide swath of science topics, many of which aren't covered by other writers.

Dr. Drang is fairly well known in certain nerd circles. He remains anonymous online because his day job is engineering consulting for lawyers working on cases that may end up in court. He feels that keeping his online presence separate from his day job is the best choice for him. Nevertheless, he often posts really great stuff related to math, engineering and physics.

February 06, 2013

Python learning opportunity

I have an honors student this semester who is working on vpython simulations of general physics systems.  She knew no programming as of two weeks ago, but tonight was really close to having a projectile motion simulation done.

In trying to put velocity vector components on the projectile's position every 10 time steps, she was running into a problem: using the modulus operator only worked on the first two vectors, then did not.

Here was her code:

 while ball.y >= -2.75 and int_velo > 0:  
   t = t + dt   
   ball.pos= ball.pos + ball_velocity*dt  
   ball_velocity.y = ball_velocity.y - 9.81*dt  
   if (t*100)%10 == 0: #doesn't work!!!   
     vel_xvec = arrow(pos=(ball.pos.x,ball.pos.y,0), axis=(int_xvelo,0,0), shaftwidth=0.5)    
     vel_yvec = arrow(pos=(ball.pos.x,ball.pos.y,0), axis=(0,ball_velocity.y,0), shaftwidth=0.5)  

The comment tells the story. I guess I should know more about the modulus operator in python. It seems simple to use, but I couldn't really figure out what the problem was initially.

The short version of this story is that my student gets to learn about computer round-off errors and how to debug code by sticking a print command in the code so that she can figure out these problems without too much intervention on my part.

Here's my debug line I ended up using, followed by the fixed if statement:

   print t, t*100, (round(t*100)%10.0)  
   if (round(t*100)%10) == 0: #works now!!!   

I'm looking forward to a fun semester of python projects!