December 05, 2012

Some of my favorite astronomy images

Today was the last day of the semester in astronomy.  I showed three of my favorite images of all time as a part of our discussion of cosmology in class.  Presented with minimal comment, here they are:

This is the WMAP all-sky image of the cosmic microwave background. The difference in temperature across the entire sky as shown in the above map is less than 400 microKelvin!

The above image is the Hubble Deep Field.  This was taken in December 1995 after the Hubble images a patch of the sky that had apparently nothing in it. After 100 hours of exposure time, the assembled photo showed about 3000 distant galaxies. This image has reshaped how we view the universe.

This is an image taken by the Voyager 1 probe. The spot in the photo is what Carl Sagan refers to as the "Pale Blue Dot". It's what the rest of us call Earth.

I've shared this video that a student made for astronomy class before, but it's worth posting here again:

August 22, 2012

Is there value in self-promotion?

I'm trying a small non-scientific experiment tonight that you're a part of.

I've been struggling with the question of the value of linking to my blog posts on twitter.  It feels narcissistic to me to post every link on twitter.  Isn't anyone who cares about what I've written going to find my stuff in their RSS reader of choice or come back to the blog periodically anyway?  If my posts are good, they will get shared on twitter and/or facebook naturally, so I shouldn't have to link to them myself, right?

My primary audience is myself, so I shouldn't have to link to anything.  But, I do hope that somethings I say are useful, or else I would not bother to put them online. Plus, I know many people don't use RSS readers, and in lieu of the feed readers prefer to use twitter to discover blog posts.

So, I'm looking for thoughts from my loyal (also smart and attractive; did I mention I don't mind kissing up?) audience.  How do you prefer to find out about my blog posts?

Since this is a non-scientific experiment I am conducting, I will do the most non-scientific thing I can think of: state my hypothesis that I am testing.  ;)  My hypothesis is that my audience is too small (and smart, attractive and polite; there is no adulation I will not give out to you; I have no shame here, only on twitter) to give me any meaningful results of this experiment.

If I'm wrong, though, please feel free to leave me feedback via your preferred channel.


Think Like a Physicist - Introduction

The first time I ever taught an introductory physics course from top to bottom was as a last-minute summer replacement hire at small liberal arts college.  The schedule was intense: four hours a day every morning and two hours of lab 2-3 afternoons a week. I know I wasn’t the best classroom instructor, but we had a pretty decent lab and the students who took the class and worked hard did make it through, and most importantly they did learn some physics.

One issue that came up, though, about ⅔ of the way through the summer was that the students confessed that they hated the quizzes and exams I gave them, not because they were terribly hard, but because they felt like they could never guess what I (their instructor) was actually thinking when I wrote the question. At first I felt like my worst fears had been realized: that I had wrote confusing and impossibly hard problems. But after talking with them, I came to realize that the level of the questions had been appropriate, it was just that they were trapped in a way of thinking which led them to believe that if they could figure out what I was thinking, they would be able to figure out the answer to the questions.

My response was that the only thing I was thinking was that if they applied the physics principles which we had discussed in class, no student would have any trouble answering the questions.  Clearly, all of the students would breeze through the summer, all of them would earn an A for the course. Of course I was wrong.

I spent much the rest of the course trying to persuade the class that they did not need to be mind readers in order to do well. I’m not sure how many of them actually believed me, but the experienced had a profound effect on my teaching. Ever since then, I’ve tried to do my best to make the physics concepts the central focus of all the classes I teach. It has been a hope of mine that no student would waste any precious study time trying to divine what is going on inside my head.

But, as I looked back at that experience during the summer I first taught physics, I’ve been starting to wonder if maybe there was a lesson that I missed myself. What if the students weren’t so much trying to read my mind, but instead they were trying to think like me? Isn’t that what I wanted? The difference may be subtle, but important, I think. When students are trying to read my mind, they are looking at a problem or question and trying to guess what the professor WANTS them to say. When students are looking at a physics situation and trying to think like their physics professor, they are trying to apply the thought processes and analysis skills of a physicist.

That is exactly what I want from my students.  I want them to think like a physicist.

August 21, 2012

First online video assignment (for students to complete)

This assignment will be a little bit different than many of the video assignments I'm going to ask you to do this semester.

I want you to make a video using your hand as the moving object. Let the edge of a table or counter be the straight line along which your hand moves. The center of the table will be the s = 0 position. Positive position numbers will be to the right and negative position numbers will be to the left.

For each of the graphs below, I want you to interpret the position versus time graphs by performing the indicated motion with your hand. As you are executing the motions, explain all the details such as speeding up, slowing down, reversing direction, standing still, moving at constant speed, etc. You should have your hand at the appropriate position at t = 0 and at the end of the time history and be able to explain that, as well.

For each position versus time graph, sketch the corresponding velocity versus time graph and explain why the velocity vs time graph corresponds to the position vs time graph.

(Credit for this homework question goes to Arnold Arons. Credit for screencast/online video assignment goes to Andy Rundquist.)

August 14, 2012

A simple genetic drift simulation

Here's the tl;dr version of this post: I wrote a genetic drift simulation that you can download and play with if you want.

When I was in high school, I had a really great teacher for biology. That's not just me saying that; she won awards at the state level honoring her as a great teacher. I don't remember all the topics that we covered in that class, but I do remember that she took me on a tour of the brand new (at the time) microbiology facility at Iowa State University. Besides being a really shiny building, it was the first time I had ever seen biology being done with computers.

Last year when I started teaching at the community college, one of the biology professors said he wanted a genetic drift simulation. He explained what he was looking for, and I nodded politely, only vaguely following along. (That's physics training, for you.) After I read a bit about genetic drift, I found an example of a very simple genetic drift simulation activity. I thought something similar would be doable in python.

Here's the user interface for the simulation:

 It is extremely basic.  All you do is choose the size of your population and the number of generation that you wish the simulation to run for.

Here is an example of a small population run for 100 generation:

As you can see, this simulation started with the Q (recessive) allele making up 70% of the population.  The P allele is quickly wiped out of the population.

Here is a simulation of a much larger population:

For a large population the simulation will start with a much closer match between the P and Q alleles. It was almost 50/50 in this run. And, after 500 generations neither allele has been eliminated, although the Q allele is starting to have a significantly higher fraction of the population.

Here's a snippet of the code that does the actual simulation part.  The mechanics of the simulation is explained in the comments:


I like this because 1.) It quickly shows the difference between genetic drift for large and small populations, and 2.) the simulations start with random conditions and have random progressions, but over a large set of simulations clear patterns emerge. I could envision a class of students running the simulations multiple times each, then compiling the data together into a class set where more conclusions are drawn.

Hopefully my code is expandable.  I'd like to add features, such as setting the initial populations, selective processes, and possibly multiple traits.

In case you want to try this (PLEASE TRY IT and give me feedback) you'll need: python, matplotlib, numpy, and Qt runtime libs.  Maybe you'll need more, I'm not really sure.  I needed coffee when I was working on it.  YMMV.

August 10, 2012

Getting information from students - Fall 2012

Hat tip to my source of many awesome things - a local high school teacher - for this idea.  Instead of students filling out an index card of information so I can get to know them, I have them fill out a form which I create in Google Drive. I post the form to the course web page, then point them there.  This way, all the information is in a spreadsheet which I can review anytime throughout the semester from anywhere.

I added the question about the smartphone this year to try to get a sense of how much I can try to get get my classes to do interactive things with them. 

The form is below...(for now)'s not the real form, but it is a copy of the one I'll put out on the course page.


Acceleration data of a (hypothetical) airplane

Hypothetically, if one were to be on an airplane in possession of a smartphone with the right app, one could hypothetically gather acceleration data of the planes motion.

I (hypothetically) was on a plane earlier this summer and (hypothetically) had my phone in airplane mode running the data gathering program with the display off until the plane landed and reached the gate.

My phone has a 3-axis accelerometer built into it.  The figures below show the orientation of my (hypothetical) data gathering.

I figure that I should (hypothetically) let the data gather for 5 minutes and hope that the landing happens in that time.  After starting the data logging app, I turned off the screen and set the phone on the floor by my feet.

Here's the acceleration data:

In the z-direction, you can see the setting down and picking up of the phone at the start and end of the graph. (Note the full 5 minutes was not used.) The acceleration is fairly constant around -10 m/s^2, due to the gravitational field.  What was interesting to me was that the average value before the (hypothetical) touchdown was the same as after touchdown, although definitely not as smooth.

In the y-direction you can again see setting down and picking up the phone, as well as the (hypothetical) landing event. There is an acceleration in this direction as the plane turns to head towards the gate.

But what we really care about is whether or not this plane is going to stop moving at a high speed in the forward (x) direction.  The acceleration data here is interesting! The maximum acceleration is about -3 m/s^2.  There are several braking events which happen.  Does constant acceleration apply here? Over certain intervals the acceleration is approximately constant, but not over other intervals.

Now I know what the acceleration of a plane landing is (hypothetically) like.  Want the raw data? Here you go. Hypothetically, I would like to know what the acceleration of a plane is like on take-off, but I don't have another (hypothetical) plane trip scheduled for awhile.

Always follow the instructions of your flight crew. You don't want to pick that fight. You will lose.

More free (libre) physics drawings

Some time ago I posted a bunch of Creative Commons licensed physics drawings that I made for class.  I've added several more drawings and posted them as a page here, where I intend to keep adding more of them.

The thumbnails don't really show the full resolution of the drawings.  You'll have to open up the files and export the drawings at whatever resolution you need.

I hope these are useful to instructors (or anyone, really) which is why I'm using the CC licence to encourage people to make use of them.  Let me know if you find them useful, and if you make improvements to them, please share them with us (that's the ShareAlike part of the licence).

August 09, 2012

One of my summer books

Radar, Hula Hoops and Playful Pigs: 67 Digestible Commentaries on the Fascinating Chemistry of Everyday LifeRadar, Hula Hoops and Playful Pigs: 67 Digestible Commentaries on the Fascinating Chemistry of Everyday Life by Joe Schwarcz
My rating: 3 of 5 stars

This book is a good and easy read. Schwartz clearly knows his science. The overall point he makes about science being a process of uncovering new incremental discoveries is a great idea which cannot be emphasized enough. What left me wanting more, though, was that he rarely described the evidence science has to back up its claims. In an effort to reach the general public, he leaves out the details that makes science what it is: a continual quest for knowledge of how the universe works. I wanted less scientific facts and more description of how we know what we know.

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July 31, 2012

Clearing my browser

Here are some blogs I'm not reading enough:

Teach. Brian. Teach.  - Brian Frank is writing quite a bit about how students respond to questions and whether or not they can explain possible misunderstandings that other students might have. He's doing some interesting mining of Khan Academy comments, without watching any of the videos.

Research You Should Know - Raymond Johnson (fellow UNI alum - Go Panthers!) has a long running series where he highlight math education research that is interesting or important. Not all of it is directly relevant to physics teaching, but there is so much good stuff there, it's tough to not get drawn in to it.

Great posts about the physics of music - from the view of a scientist and from the view of a musician.  It's neat to see this dialog happen online.

It's Okay to be Smart - This is a relatively popular science link aggregator, but new to me.  Some of it is not for me, but I find enough on here that otherwise I would have missed.

Learning About Teaching Physics - An extremely well produced podcast about education research related to teaching physics.  I wish they would make more of these!

Enough link dumping for now...

July 26, 2012

Break the cycle of Khan Academy criticisms and responses

When I first started interacting online (other than just via email) one of the most valuable lessons I learned was to "not feed the trolls". A troll is a person who posts in order to get a reaction from someone else in the hope of continuing an argument online. The "food" that a troll thrives on is attention.

For the most part, I do pretty well not feeding trolls online. But certain discussions about Khan Academy (KA) inevitably suck me in; I forgo protocol and end up in pointless discussions online trying to argue the points that numerous educators are trying to make about the shortcomings of KA. Since the KA has been used millions of times by (likely) millions of people, there are plenty of people who come to the defense of the KA and all that they do.

The KA defenders typically have a standard litany of responses to any criticisms of the KA.  Most of their responses don't actually address the criticism, though.  It makes it really hard to have a discussion about how to improve how the KA can reach its mission of providing a free world-class education for anyone anywhere.

The typical responses to KA critics (and my thoughts on them) include:

  1. The critics are just jealous of Sal Khan and his success.

    This, by far, has to be the most ridiculous and possibly most common response. (Haters gonna hate is a subset of this response.)  No educator that takes time to write a piece about the work that KA does is any sense jealous of the KA. The critics of KA are passionate about high quality education. They genuinely love the work they are doing. Anyone who loves what they do for a living does not begrudge another person success in doing what they are passionate about doing. Sal Khan is passionate about providing a free world-class education online? Awesome! We are passionate about world-class educations in our classrooms.  By the way, we've been teaching these classes for several years (sometimes multiple times a day) and we have the experience of knowing what concepts students struggle with in our classes. We'd like to suggest that the KA consider changing how they approach these topics if they want to reach their goal.

    There is no jealousy, only collegiality.
  2. The critics are worried that they are going to be put out of business by KA.

    You can easily search the internet to find articles about KA which include claims that some people think that KA threatens the security of teacher jobs. I have yet to meet a teacher or school administrator who actually believes this to be a possibility. Sal Khan himself has said that the goal of KA is not to replace teachers. The argument on the face of it makes no sense. With no teachers, there are no schools. No schools means that every household becomes a de facto homeschool operation. It seems unlikely to me that this would ever happen anywhere in the K-12 environment, let alone college.

  3. Why don't you go out and make your own set of videos?

    Generally speaking, an educator's job is not to make educational videos. Some teachers have, though, mostly for use in their own classes. I have made videos for my classes in the past, and I feel they served a useful purpose for the classes I was using them in. My videos were made for specifically for the classes I was teaching that year, and I would not expect them to be optimized for anyone to watch them and fully learn the material. The KA is attempting to provide video that can be watched by anyone at anytime, so they have a different way of structuring their videos. Some educators believe that the video format is not the correct way to introduce topics to a novice. That is a separate argument that may be worth having some other time. I'm guessing, though, that the KA is not going away anytime soon. Since it has so much traction, why not try to have the KA post the best pedagogical content that can be produced? Video may be imperfect, but it can be made better.
  4. My teacher sucks/sucked. I read the material and went to my teacher and I still didn't understand anything until I watched the KA videos.

    Eric Mazur frequently repeats the old chestnut that "the plural of anecdote is not data". So although there are dozens/hundreds/thousands/countless of people who claim that they were the victim of substandard instruction we have no way of knowing if all (or any of them) were truly in a class with a poor teacher. Honestly, we have know way of knowing whether or not learning truly happened just by you reporting that you made it through a particular class with a particular grade. An alternate explanation to their experience was that the struggle which the KA supporter went through was ultimately more useful for the learning of the material. It may be that using all the different methods of trying to learn the material, the student was engaging in deep processing of the concepts, the last step was seeing the KA video. So, it's not specifically the KA video, but the overall process of studying which led to learning.
  5. The videos aren't a replacement for teachers; they are meant to flip the class in order to make class time more interactive. Or they are meant for review and refreshing topics.

    The idea that many students would use KA as a review or method to brush up on topics no longer fresh in their minds is not a bad thing at all. But then, let's not hail KA as a revolution in education, okay? Sal Khan is not a trained educator, and while he may be relatively good at explaining his understanding of certain topics, it does not mean that his way of understanding is the best for everyone. He demonstrates knowledge of the content in the videos (mostly he does it acceptably) but often it is at a superficial level. More troubling is that he demonstrates a lack of the pedagogical content knowledge.  That is, he lacks the understanding of what it is that makes a topic difficult to understand. Furthermore, the videos are a one-way street.  There is no way for him to know if anyone watching the video is truly improving in their conceptual understanding.
  6. The videos are better than sitting in class. You aren't distracted by anything because all you see is the digital blackboard and all you hear is Sal Khan's disembodied soothing voice.

    Okay, fair point. Life is filled with lots of distractions. School, no matter what level, is no exception.  If what you need to focus on learning is a digital background with a calming voice leading you through the steps, then KA has a place for you. However, there's is so much more to learning and doing science and mathematics (two of the most prominent topics of KA) than just sitting and watching a digital blackboard!  The KA, with this limited approach, cannot help you perform experiments, take data, do video analysis, perform simulation, or otherwise engage in the material. (KA may be planning to implement some of these ideas in the future, but they are not there now.)  And what stuns me, is the number of KA supporters who claim to be bored by their teachers at school, because all they do is stand in the front and lecture, but they love KA.  What's the difference? Just because it is online doesn't mean it isn't the same delivery method.  Except, you can't ask Sal Khan to clarify or give an alternative example. Sal Khan doesn't have office hours.
  7. The KA is not only about the videos! It has exercises and metrics and badges!

    Not all learning can be quantified by computer-scored exercises. I'm much more interested in what a student knows conceptually, and that tends to require more individualized attention from a teacher.  The metrics tools may be useful for tracking students progress through the KA exercises, but since the exercises don't measure the full picture of the learning of my class it doesn't do much for me.  As for badges, well I do love a good game. But, what about encouraging learning for its own sake? How can we emphasize the importance of pure curiosity if we reward everything with meaningless badges?
  8. Don't you get it? The KA is for middle school math/freshman high school math/remedial math/high school science/introductory classes/third world countries and NOT for graduate level coursework.

    Well, I get it. KA is for anyone at anytime. But that flexibility means everyone at every level can watch any video. Although it is not always explicitly stated, I believe that KA has some vague notion of the target audience for each video that is posted. I don't believe that the fractions videos are intended for college sophomores, nor do I believe the organic chemistry videos are intended for fourth graders. Yet students from both levels are using them. And while much of the content is not intended for advanced levels of study, why should that mean that the presentation should be sub-par? My general education courses that I teach to non-science majors are still legitimate college science classes. I have high standards for myself and for the class. The content is approached differently than I would approach a senior-level course for physics majors, but the standards for the class are still equally high. Why should KA have lower standards? Why should users of KA accept that the videos have mistakes or bad pedagogy in them? They shouldn't.
  9. I'm sick of hearing complaints about KA. KA is great and if you don't like it, don't use it.

    Frank Noschese famously posted on his blog "My final remarks about the Khan Academy" and then a few months later, started tweeting more about KA. He's not the only one who has pointed out problems or issues with KA.  I hope that fans of the KA would see that the educators pointing out the problems with KA are not out to shut down KA or stop Sal Khan from doing what he does. It's because these teachers care about the quality of education that they take the time to point out the problems. If you love KA, you should want it to be better than it already is. Help us out by encouraging the Khan Academy to engage with the educators who have been reaching out to them.
To all of Khan Academy users, please know that we've heard your responses to our critiques. Before you reply to us with one of the typical responses, please consider what we are all looking for: better education for everyone.

July 18, 2012

Local musicians - Jonas Friddle and the Majority

I just heard a great group of musicians from Chicago's Old Town School of Folk Music called Jonas Friddle and the Majority.  Check them out!

July 02, 2012

Invitation to the Khan Academy

I've been watching the unfolding of Justin Reich and Dan Meyer's "Mystery Teacher Theatre 2000" challenge over the last week or so.  Last Friday, Rhett Allain posted his critique of a kinematics video from the Khan Academy.  Over the weekend, Sal Khan posted a "correction" to Rhett. Lots of angry comments were posted all over the internet, and we've got the makings for a mini-internet soap opera. 

I remember when I first started teaching, hearing all the retired teachers who were still coming to AAPT meetings yammer on about how careful you have to be when choosing words to describe the introductory topics.  Mixing up "throw" and "drop" was something I probably did the first two years I taught physics. Other teachers with decades of experience helped me understand how I could be making it harder for students to understand the more challenging topics later by not being as precise early in the year. The more experienced teachers showed me a better way, and I became a better teacher.

I see a lot of what I was doing in my first years of teaching in the Khan Academy videos.  Sal's attempt to correct Rhett illustrated (at least to me) that he truly does not have a deep conceptual understanding of the introductory physics material.  That's not to say that he is not good at explaining what he does understand. He lacks the depth of conceptual understanding which students NEED for meaningful learning. Of course, the Khan Academy has said that their videos are only a part of a student's learning process. But  I don't believe that his videos are optimized for effective learning.

I also don't think that the Khan Academy is going away anytime soon.  Since I believe that anyone can improve their abilities, I thought I would provide Sal Khan some feedback in the style of the coaching that I received from the Global Physics Department last year.  I chose a series of videos about a topic in astronomy, watched them all, took notes and recorded my feedback.  Here's my feedback video:

I hope the Khan Academy is willing to take my feedback and use it to improve their videos. I really do.  We need more GOOD resources in this world.

What I hope comes out of the MTT2K competition is that the Khan Academy would engage with the physics education community at a meaningful level. Engagement between educators should be a two-way street, though. I want a dialogue between physics teachers and the Khan Academy. So here is my invitation to Sal Khan:

Sal Khan, you are always welcome to chat online with us in the Global Physics Department meetings on Wednesday nights. Let us know if you're free at 6:30 pm California time on a given Wednesday and we'll set you up. Or, if you don't mind traveling why not come to a meeting of the American Association of Physics Teachers? I won't be in Philadelphia this summer for the AAPT meeting, but I will be in New Orleans (that's your hometown, right?) for the winter meeting. Or, if you'd like to interact at the local section level, I will be hosting a joint meeting of two of the most active sections in the country right outside Chicago in October.  Would you be willing to come and talk with physics teachers and physics education researchers face-to-face? I know you run a non-profit, but I bet we could arrange to fly you here and I have a guest bed at home you are welcome to. Let me know!

June 20, 2012

Fixing corrupt PDFs

This is a note to my future self to remind me that when I need to fix a corrupt pdf file to use ghostscript. The relevant command was:

gs \
  -o repaired.pdf \
  -sDEVICE=pdfwrite \
  -dPDFSETTINGS=/prepress \

April 20, 2012

It's not often that I get what I want...

Apparently there is a journalist out there who is willing to do some investigation:

Since I got what I asked for in my last post, I will soon be drafting a post about how all physics faculty should be given a new car, gratis country club memberships and a new ipad every year for life.

Meanwhile, check out Rhett's videos of the hypothetical car stopping (or not) at the stop sign.

April 19, 2012

More on the braking, sneezing physicist in a car

For some reason, the story of the physicist who used science to get out of a traffic ticket has continued to hold my attention.

In my last post, I made some quick calculations based on the claims implied in the paper. My calculations showed that if the car was slowing down at the claimed rate of 10 m/s2 then the car would have been traveling at least 223 miles per hour at the low end of the range indicated on the graph. A careful reading of the paper reveals that the author does not reveal what speed he was going before inadvertently applying the brakes while sneezing.

I've never really thought much about the observed angular speed of an object passing in front of you at high velocities.  I can remember being on train platforms and watching a train approaching in the distance and being amazed at how it appeared to be going slow when it was far away, but as it passed it seemed to be going really fast.  I don't find anything wrong with the theory presented in the first part of the paper.

I do have issues with the values of the velocities purported in the paper (as I already mentioned) and the values of the accelerations (as I mentioned in the last post). So, I wanted to see what the author's graphs might look like with more realistic values for velocity and acceleration.

The first graph I made is a graph comparing what the author claimed: constant deceleration of 10 m/s2 for 10 seconds followed by 10 seconds of acceleration at 10 m/s2.  Then I made a graph of a car going at a constant velocity of 10 m/s (22 mph) for 9 seconds, slowing down at 10 m/s2, stopping for an instant, speeding up for 1 second  at 10 m/s2, and finally continuing on at 10 m/s for another 9 seconds.  Here are the two graphs superimposed on each other:

The graphs are remarkably similar, which is at first somewhat surprising, but can easily be explained. Two things that you should note from this graph: 
  1. The observed angular speeds are initially higher for the more realistic case. 
  2. The deceleration portion of the realistic case exactly overlaps the author's model.
The first point can be explained due to the fact that the car is actually much closer to the stop sign at t = -10 s in the more realistic case.  The second point is exactly what we would expect to see since both cases used the same accelerations during the time interval from t = -1 s to t = 1 s.  For the physics and math nerds reading this (and if you're not a physics or math nerd, bravo to you for reading this!) I wanted to check my method of calculating the angular speed versus Krioukov's method.  I used an approximation of angular speed by calculating  the change in angular speed between small time intervals.  With a small enough time interval, the approximation should be good enough, and it was good, since the two graphs overlapped.

Since my method was sound, I modeled a more realistic scenario for braking and accelerating: First the car approaches at constant speed of 10 m/s.  The car brakes at a maximum safe negative acceleration such that it comes to rest at t = 0 s. Immediately the car accelerates at the maximum acceleration for a Toyota Yaris until it reaches a speed of 10 m/s at which point it stops accelerating.

I used a coefficient of friction between the rubber tires and the road of 0.8.  With an initial velocity of 10 m/s, I was able to calculate the highest acceleration that would safely bring the car to a stop.  I found the acceleration to be 7.8 10 m/s2, which was not far from the estimate of 10 10 m/s2 in the original paper.  But the quickest time for a Yaris to go from 0 to 60 miles per hour I could find was 9 seconds. This corresponds to an acceleration of 3 m/s2, which is far less.  Combining these parameters into my model and comparing with Krioukov looks like this:

Using more realistic accelerations, the graph looks significantly different than the case presented in the paper.

But, I don't really care about the physics reported in the author's paper.  I believe that Krioukov wrote the paper as a harmless April Fool's Day prank (just like the 100 m telescope paper and the magnitude of the Tooth Fairy paper) hoping only to give other physicists and readers of arxiv a good laugh.

But shouldn't news bloggers do a bit more checking first? It seems wrong to just blindly accept whatever a scientist says without even questioning it. That doesn't seem scientific at all. On the other hand, whoever is running the twitter account for AAPT also seemed to be willing to accept that

Do the ends justify the means here?  Assuming the paper is a prank, then is it okay that the nonscientific public not realize that it is a farce? I'm a big fan of clever scientific play such as this, so at the end of the day, I don't really care that this stunt was pulled.

What I care about is the issue of how science is being reported to the non-scientists.  We should be able to rely on science journalists (and journalists, in general) to do some basic fact-checking to see if the story checks out.  The back of the envelope calculations I made for velocities and acceleration don't require anything more than high school physics, so they aren't out of the reach of journalists, yet countless journalists made light of the mathematics used in the paper.

More disturbing to me is I see no evidence that even non-scientific facts were checked.  Here are some questions I would be asking if I was a journalist:
  • When was the citation issued?  Can I see a copy of it?
  • When was the court date? Who was the judge? Can I get a copy of any court records?
  • What is the maximum fine (including fees) for running a stop sign in California?
Again, I don't really think there is any harm done by this story, if we can all learn something from it. I've learned that stories about the little guy beating the long arm of law are popular, even if they don't make much sense.  I've learned that some journalists do even less investigative work than I previously thought. Most importantly, I guess I've learned that we have a long way to go before we see a scientifically literate news media.

April 16, 2012

Physicist did NOT write mathematical study to get out of traffic ticket

Sometimes, I get obsessed by the silliest little details. For some unknown reason today, the story about the Physicist Using Math to Get Out of Traffic Ticket story was making the rounds on blogs and twitter again. Again? Yes, it first came around a little over two weeks ago: on April 1st. (There's your clue that it is a hoax.)

In the Physics Central write up of the "study" the author is quoted to challenge readers to find the flaws in his argument. I don't want to get into the math right now, since I don't really have the time. But, let's look at whether anything in the paper passes the back-of-the-envelope sanity tests.

1.) His acceleration/deceleration calculations are for constant acceleration of 10 m/s2 (first negative, then positive) over a time range from 10 seconds before approaching the stopsign and 10 seconds after.  So, ten seconds before getting to the stop sign he was going 100 m/s?  That's 223 miles per hour.  Kinda speedy for a Yaris, if you ask me.

2.) His negative acceleration of 10 m/s2 is about the same as the gravitational field constant. If we buy his argument in his paper of his speed being around 18 mph (8 m/s) when suddenly applying the brakes, then his stopping distance would have been 3.2 m, which is about 10 feet. That is right at the line of what we'd expect for a coefficient of friction between the road and tire of 1, which is awfully high, but not completely impossible.  It smells funny, but it doesn't fail the sanity check.  Although, I'm not sure I'd want to be in the car when braking that quickly.

3.) The positive acceleration matching the negative acceleration in magnitude, though?  Completely crazy talk.  The best acceleration of a Yaris has a 0-60 mph time of about 9 seconds, which is an acceleration of around 3 m/s2, and well under his estimated acceleration.

So, well played prank, Mr. Krioukov.  You've made crazy drivers everywhere think a little bit more about physics, even if you led them a bit astray along the way.

March 22, 2012

My student's take on the "Pale Blue Dot"

Every term when I teach astronomy, I give an assignment of an "AstroJournal" which requires, among other things, students to make observations of the moon and read news articles on astronomy and space science. There is a rubric that all the students get so that they will know how they will be graded. In the rubric is a category called "Other" which gives students a chance to put anything in their journal that is related to astronomy or space that does not otherwise fit into a category we've defined for their journal.

It is also, the only place in ANY of my classes where I give something that even resembles "extra credit".  Students can get a small amount of bonus points on the AstroJournal by including items in the "Other" category.

One student last semester was really worried that she was going to fail the class (she was by no means in danger of failing at any time, but that's a whole different discussion), so for her "Other" category she made a video that she uploaded to youtube and sent to me.

On the last day of class, student were to turn in their journal. This is when she told me about the video. She explained that she called the video "pale blue dot".  I was really surprised, because that was going to be our class discussion of the day. On the last day of class, I have two images that we spend the entire time talking about.  One is the Hubble Deep Field and the other is the "Pale Blue Dot" image from the Voyager spacecraft.  But this student had taken the initiative to learn about Sagan's "Pale Blue Dot" speech, and put the words with video.

These are the moments that you dream of as a teacher.  Enjoy.

March 21, 2012

Violin link roundup

Time for another link dump:

What Really Happened in that Double-Blind Violin Sound Test

Double blind tests – the inside story

Exclusive: how I blind-tested old violins against new

Metafilter discussion of the study

Some of these links are a few weeks (months?) old, but when we're talking about 300 year old violins, does a few weeks really matter?  I first heard about this study at the Acoustics Society of America meeting, but it wasn't until after the article came out and made the news that I really thought about it.

What I think is interesting (and great) is that the musicians were really engaged with the study that was done. You can read what three of the 21 musicians have to say about the experiment in the top three links above.  I think that these musicians really had a great grasp of what the researchers were trying to accomplish and in telling their story they do an incredible job of reaching out to other musicians to explain what the scientist were trying to study.

February 13, 2012

Measuring the speed of light in a microwave oven - is there a better way?

Did you see this video? I subscribe to the CoolStuff newsletter from Arbor Scientific.  They send out an email roughly once a month which usually has some sort of  interesting idea for a demonstration or lab activity that I can use in the classroom.

This month they included a video about how to measure the speed of light using a microwave oven. The idea is that if you put something soft in the microwave (I've seen this done with marshmallows or chocolate) and turn the microwave oven on until the first hint of melting occurs you can measure half of a wavelength of the electromagnetic wave (in the microwave portion of the EM spectrum) by measuring the distance between soft spots.  Multiply the wavelength by the frequency of the microwave wave (conveniently printed on the back of the microwave oven) and voila! you have the speed of light to within a few percent.

It's a great idea for an exploration into EM wave phenomena.  But, I was a little underwhelmed by the explanation given in the video and on the supplemental page.  I don't want to nitpick too much. Mainly, I was disappointed that the explanation given was very traditional in the way it was presented. Kind of like: "Here are the facts. Here are the equations. Here's the reason it happens. Here are our results."

There wasn't much discussion about the pattern left in the chocolate. I have questions about the video! Why was the pattern in the chocolate shaped the way it was? Was there something about the magnetron (or was it thewaveguide?) in the microwave oven that lead to this pattern?  Do microwave ovens still use magnetrons to generate microwave waves?  How does chocolate get heated in the microwave if it has almost no water content?  I thought heating of food was due to a resonance of water molecules in the foot.  (It's not.)

I took some notes on what bothered me about the explanation of the phenomena.  What did you notice about this video? Have you done this exploration in class?  How have you done it differently to make it more engaging?

February 01, 2012

Treadmill thoughts

I hate running.  But, I've learned that there are few ways to exercise which are easier and cheaper than running.  I mean, all you really need to run are a decent pair of shoes and a place to run, right?  (Barefoot runners need even less.)  Most of the time when I run (and, trust me, I don't run, I jog slowly) I am on a treadmill.  Knowing physics can be useful when you're on a treadmill.  I can pace myself and try to speed up or slow down as much as I think I need to when I want to.  But knowing physics can also be a curse when on the treadmill, since I can calculate how much longer I'll be running when I don't really want to be there in the first place.

To try to keep my mind off the running, I'm often staring at all the displays on the treadmill. One of the displays keeps track of how many calories (really kilocalorie, which I abbreviate as kCal) I have burned in my workout. The treadmill displays how many calories I can burn in an hour at whatever speed I'm going at.

One day last week when I was on the treadmill I started to think about how that rate at which I burn calories (really my power) should vary with speed.  It seems obvious that the faster I run, the more energy per hour will be required to maintain that higher speed.  But how does it vary with speed?  I made a naive guess that it would be proportional to my average kinetic energy:

$$KE = {1 \over 2} m v^2$$

$$P = {KE \over t}$$

So if my speed doubles, I would expect the rate at which I convert the stored internal energy into the energy used move at that speed to increase by a factor of four. When I asked on twitter and facebook last week what people thought about how power varies with speed on a treadmill, I only got one response from someone who said "I respectfully disagree with you." Time for some data.  I turned on the treadmill and started recording the rate of calories burned at each speed from 0.1 miles per hour to just over 7 miles per hour.  Here is that graph:

So, as you can see, the graph has two distinct regions, which are both linear.  The discontinuity occurs at around 3.7 mph, roughly where it becomes too difficult to maintain a walk, and I have to switch to a jog to stay on the machine.

I'm a little surprised by this graph. In case you're wondering, I did not enter in my weight or height or age into the treadmill.  I really don't even care if the power values are correct right now.  I'm was puzzled by why the trend is so linear.  Let's go back to the definition of power, I said power was related to the kinetic energy.  It would have been more correct to say power is related to the work I am doing:

$$P = {W \over t}$$

Since I assumed that all of my work went into kinetic energy, I don't feel too bad about the earlier statement.  Work is $\vec{F} \cdot \vec{d}$ or just $Fd$ if the force and displacement are in the same direction, so power is:

$$P = {Fd \over t}$$

But $d \over t$ is my speed!  Oh, so I should write my power as:

$$P = Fv$$

where $v$ is my speed.  Oh, this is linear.  I guess the treadmill designer got it right.  Bummer, I was really hoping to burn more calories by just increasing the speed a little bit.

January 31, 2012

All of physics in one diagram - via Creative Commons

Today, this came across my twitter stream:
I thought it was really cool that Ian had encapsulated many of the connections between the various branches of physics.

I couldn't help but notice, however, that one branch of physics which is near and dear to my heart was missing: acoustics.

I'm not sure why acoustics tends to not be taken seriously by some physicists.  Waves are fundamental to our study of physics, and sound is one example of a type of wave that we can study. Acoustics is a highly interdisciplinary field.  Scientists who use acoustics include biologists, physicists, medical doctors, medical physicists, neurologists, psychologists, geologists and astrophysicists. Astrophysics?  Fields like helioseismology and astroseismology look at the vibrations of the Sun and stars to study their interiors.  Acoustics tells us about the beginning of the the Universe.  And some planetary scientists have even proposed studying the subsurface ocean on Europa with acoustics.

Acoustics isn't easy, either. (Equations for the vibrations of thin plates involve fourth-order differentials.)  It's not like we've stopped learning about how sound behaves or how humans perceive sound.

So, I was thrilled to see that Ian released his diagram under a Creative Commons license.  I have given him appropriate attribution, and am releasing my revision of his Prezi under the same license.

Enjoy in full-screen mode.

January 23, 2012

Time for active reading in my class

Last week, Apple made a major announcement about their entry into the textbook market. The best criticism of Apple's plans was given by Audrey Watters.  I'm not going to recap what she said. You must read it for yourself.

And, if you are a believer that all textbooks are crap, you probably won't have much use for what I have to say here, either.  I'm often surprised by the number of teachers (college and high school) who have no use for the textbook. And, sorry Frank, building ramps doesn't count:

(Although, Frank does have some good ideas of what a physics ibook could look like.)

I do believe that it is my responsibility to (as much as possible) choose relevant and well-written texts for use in my classes. I also believe that there is no perfect textbook.

I have introduced to my calculus-based class what I am calling active reading.  The class has already been assigned readings from the text to complete before coming to class.  They complete short reading reviews online before the class starts that I look at before class starts.

But this is not enough.  Active reading requires:

  1. Note taking while reading. Both in the margins and in their notebooks. Underlining and judicious highlighting are also encouraged.
  2. Access to other reference materials, such as dictionaries or the web for looking things up.
  3. Repeated reading. My class knows that their first time reading through the material I don't expect them to become experts.  I do expect mastery of the concepts we cover in class before the next quiz or exam.
I don't think we do enough in the sciences to teach our students how to be active readers. I don't know how we can correct this deficit, but I think it's something that is long overdue.