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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