September 12, 2016

Day 11 - PHYS 201 and PHYS 110; A favorite physics puzzle

Last Thursday was Day 11 in Physics 201. We have wrapped up discussing vectors, so the next topic is projectile motion. To start this topic, we got out the ballistic cart apparatus and had the class investigate: traveling on a horizontal track vs. on an inclined track AND dropping the ball vs. launching the ball from the cart.

This is one of my favorite physics puzzles to explore in introductory physics. I heard at least two groups talk about how their trial "didn't work right" because the cart caught the ball when it was going down the incline.  So, they made the angle larger and then tried again - and again were surprised when the cart caught the ball. Great investigation technique here by the students - now we have to work on the analysis.

In Physics 110 we finished up talking about the first five conceptual objectives - including talking about homework questions and practice assessment questions. In terms of new material - we defined longitudinal and transverse motion of coupled oscillating systems. In the previous class we had the air table out (no photos) but this day we used the PhET simulation to explore coupled oscillators:

Normal Modes

Click to Run

We also got out the snaky springs to discuss basic wave behavior.  Working as pairs, the class explored the following ideas:
  • A wave pulse, showing the transfer of energy.
  • Reflection of wave pulses
  • Transverse vs. longitudinal
  • Frequency
  • Wavelength
  • Speed
  • Wave speed depends on the media.
  • Interference.
  • Standing waves.
  • Generation of harmonics.

September 07, 2016

Day 10 - PHYS 201

Today in Physics 201 we finished discussing all the TIPERs related to vectors.  One of the questions involved considering the orientation of the coordinate system.  We had good class discussions about that question.

Also, I shared my version of the "Problem Solving Process" including this poster hanging in the front of the room:

I guess it is clear that I'm not a graphical designer. ¯\_(ツ)_/¯

September 06, 2016

Day 9 - PHYS 201 and PHYS 110

What happened to Day 8?  I forgot and the Labor Day holiday happened, that's what. :/ (Last class was starting vectors, finishing the intro to coding, and doing the first assessment.)

Today in Physics 201 we started vectors in the 8:00 am section and got both sections going with the nTIPERs related to vectors.  I used the PhET simulation for vector addition to get the discussion going, then turned the class loose on the nTIPERs.

Here's one student's artwork with the sim:

I like it!

In the 10:00 am section we had a bit of time to discuss misconceptions from last weeks assessment.  I showed some photos of answers given by students on the assessment.  Surprisingly to me, the students self-identified their own work.  I hope the discussion was positive and productive.

In Physics 110 we looked at coupled oscillators, including getting out the air table for looking at pucks and springs coupled together.  We also finished the work with the IOlab devices and measuring the spring constant with them.  We finished up class by doing some end-of-chapter problems from the first two chapters. First assessment in this class will be next Tuesday.


August 31, 2016

Day 7 - PHYS 201

Today in Physics 201 the 8:00am section finished up the TST activities and then did some nTIPERs related to the 1-D motion.

In the 10:00am section we looked at python for the first time.  I stole material from Rhett Allain's introduction to coding - starting with the class looking at constant velocity and constant acceleration motion.  We used, which I think I'm going to stick with as long as possible.  Here's the code we started with:

One note - there was a bit of trouble running the code on the classroom laptops. I'm not sure if it is becuase we use Internet Explorer or because I chose to use GlowScript instead of straight python. I'll need to look at this more.

August 30, 2016

Day 6 - PHYS 201 and PHYS 110

Today in Physics 201 we continued with the TST activities from yesterday.  The 8:00am section started them, and the 10:00am section finished them.  In the 10:00am section we did a few more TIPERs after completing the lab activity.

In Physics 110 we looked at the data from the PhET simulation. Students were shown how to plot force vs. stretch distance. The goal I was heading for was developing the idea of a spring constant and Hooke's Law  I wanted to try to make the analysis more real to try to illustrate what we are trying to measure.  So I had this set up (thanks to our awesome lab prep staff!) in the lab:
Springs with identical hanging masses.
The springs all had the same masses hanging from them, thus the same force.  Students easily understood that the spring with the least amount of stretch was the hardest (in terms from the PhET simulation) and the spring with the largest stretch was the softest spring.  We will follow up on Thursday to see how the understanding is progressing.

Day 5 - PHYS 201

(Day late...oops.)

Today in Physics 201 we got the 8:00 am section caught up with the calculus-based derivations of the kinematic equations.  The 10:00 am section asked some questions from the homework which led right into the "Tools for Scientific Thinking" activities which involve students walking in front of the motion detectors.  We only do the first 3 of these activities.  With some encouragement and bit of pushing, most of the groups got through the first two activities in a little over an hour.

Students working on the "Tools for Scientific Thinking" activities.

A better way to give practice problems?

Is it better to do traditional physics problems...or would there be value in structuring problems so that the answer is stated in the problem?

For example, when I think of a "traditional" physics problem, I think of something that looks like this:
If air resistance is negligible, determine the maximum height (above its release point) of a ball that is thrown straight upward which is in the air for a total of 3.0 seconds. 
But, what if the problem were stated more like this:
Show that when air resistance is negligible, a ball thrown straight up that is in the air for 3.0 seconds reaches a maximum height of 11 meters above its release point.
In my mind, the second version explicitly puts emphasis on the process and the reasoning behind the process, whereas the traditional problem naturally emphasizes the answer to the question.  I can see this way being done in the classroom setting, for homework practice as well as assessment purposes.

What am I missing here?  Why isn't this done for intro physics classes?

August 29, 2016

Embedding PDFs in a LaTeX file

Have you ever wanted to embed a PDF inside a larger LaTeX document?  For my "Book of Infinite Learning" I wanted to embed a copy of two different journal articles.  I didn't want to just grab the text and redo the layout of the articles.

Fortunately, there is a LaTeX way to do this.  Here are the commands I used:
\includepdf[pages=-, fitpaper=true]{filename.pdf}
The heavy lifting is done by the \includepdf command from the pdfpages package.  Read up on the options for that command if you don't want to use all the pages in the file.

What really made my day was the ability to change the margins for my LaTeX document for just the PDFs I wanted to embed.  Using \newgeometry I can specify smaller margins for these pages, since the PDF already has plenty of margin spacing.  Then \restoregeometry reverts back to the document margins.

I'm very happy with how this turned out.

August 26, 2016

Do you know about booklet printing?

I need to make a confession. I may have a problem.

I'm addicted to booklet printing. 


Last Spring at the start of the term I was fretting about whether to give paper copies of my syllabus or stick only with the online version. 

I may be kidding myself, but I am trying to use a well-formatted layout for the syllabus so that it is easy and welcoming to read. I know not all students will read it, but I want to remove as many barriers as possible. 

The real issue was the page count. I had 80 students and an 8-page syllabus to hand out. Even double-sided, that's a lot. 

Enter booklet printing. 

It's an option on Adobe Acrobat to print foldable booklets. That puts four pages on a single sheet of paper. What's that? You don't want to hand out super small booklets made on standard sheets of paper? Print on legal paper - then each page is 8.5" by 7". 

I do TIPER packets this way and other random handouts that I create for my classes. Now practically everything is booklet printed. We save paper and the multiple sheets are easier to keep together. 

What do you booklet print?

August 25, 2016

Day 3 - PHYS 201 - No class

(This was supposed to be published yesterday, but I wrote it on the plane home and the on-board wifi wouldn't let me publish it, so it was shoved into a drafts folder.)

We did not have class today because I was at the Office of Science and Technology Policy at the White House. Technically, the meeting was at the Eisenhower building - which is where the majority of the President's staff work every day.


Day 4 - PHYS 201 and PHYS 110

Today in PHYS 201 we connected the motion diagrams to graphs and introduced concepts: position, displacement, average velocity and average acceleration. We also discussed the connection of the slope of a graph and that taking a limit as the time interval becomes small leads to an instantaneous velocity or acceleration. The 10:00 section was able to use calculus to go from a constant acceleration back to an expression for position as a function of time.  That section also got the first packet of nTIPERS.

The PHYS 110 class started by looking at the class data from the previous mini-lab. It was not as clean as I'd hoped, but we talked a bit about variance and uncertainty in data and how to improve that.

Then we followed that discussion up with one of my favorite demos - taking a set of 5 balls of various sizes and masses and challenging the groups to order them by weight.  The key to this demo is that there should be a small steel ball which weighs LESS than a larger foam ball.  Most groups will say the metal ball is the heaviest.  Today there were two groups that said the foam ball was not the lightest, but the other four groups said it was.  Students are amazed to learn the foam ball is the heaviest and the steel ball is less massive than two of the balls (at least) in the set.  It is a dramatic illustration of the body's sensitivity to pressure.

After finishing up the intro to basic physics, we started on Simple Harmonic Motion and got through part of the PHeT demo on Masses and Springs as a mini-lab

Masses & Springs
Click to Run

August 24, 2016

The physics of steadicams - a lab idea?

I recently heard a podcast on the design and operation of steadicams by the excellent Stuff You Should Know podcast. The podcast took much of the information from this article: How Steadicams Work | HowStuffWorks.

The part of the article that caught my eye the most was this:
Increasing the object's moment of inertia makes it harder to shake the camera unintentionally. One way to increase the moment of inertia would be to add more weight to the camera system, but this would make things harder for the cameraman. Instead, Garrett Brown decided to take the existing components of the camera and spread them out. This increases the distance between the axis of rotation and the mass of the total camera assembly, making the camera more resistant to rotation.
I wonder if it would be possible to develop a physics demonstration, or better, a lab based on the physics of the steadicam.  I know there are some consumer-grade steadicam mounts, but I'm not sure if those would be useful for a physics lab.

I'm just brainstorming here, but what if there was a lab where students had a goal of developing a steadicam mount for either their phone or a camera that we have in the lab. There might be constraints on the construction or mass of the mount and/or some sort of guidelines on the assessment of the effectiveness of the mount.  Or maybe what would be even better is if students developed their own methods of assessing the effectiveness of the mount.

I'd love to hear your thoughts and ideas related to steadicam physics.

August 23, 2016

Day 2 - PHYS 201 and PHYS 110


Today in Physics 201 we looked at the motion diagrams posted on the New York Times website as an introduction to 1-D motion. 

Then I challenged the class to make their own motion diagrams using a blinking LED on an arduino captured with a long exposure photo. My idea was to use the exercise as way to have a goal, try something out, analyze the results and iterate until reaching the desired outcome. I think it worked all right, but I wish we had more time. 

In Physics 110 we introduced ourselves to each other and then started getting into the basic physics material. I passed out the syllabus and went through that. 

We got all the way through the first "mini-lab" I had set up, which was finding the acceleration of the IOLab carts going down a small ramp. I realized as the class was doing the lab that I have no idea how to save the data. Oops. Going to need to figure that out!  

August 22, 2016

Day 1 - PHYS 201

Today in PHYS 201 we did this excellent activity which was linked to on twitter.  I'm glad I saw it and tried it out with the classes, because I had run out of time after having the class do the FCI and handing out the syllabus.  Having only 90 minutes each day is going to make each day seem tighter, but I think overall it will be better.


Acoustics videos by the Smithsonian's American Museum of Natural History

I only recently discovered that the American Museum of Natural History has a few videos on acoustics.  These videos are short and pretty good. They all have native captions in the videos, which is a great feature.

The above video shows off quite a few historical scientific devices for studying acoustics, but other than mentioning a wave machine, does not really discuss much about the specific devices. My question: how many examples of the devices shown are still being used in labs and classrooms around the world?

The second video in the series is about the concept of waves and the propagation of sound as a wave. Again, the video is short, but the science is solid.

The third video is all about tuning forks. I think the science here is a little less well done, although it is passable for introductory level acoustics.  That said, there's not a whole lot of interesting or relevant science being conveyed in this video. Some interesting history, but that's about it.

The fourth video is about Chladni's demonstration of mode shapes of vibrating plates. This video is really short.

The last video in the series is an introduction to the idea of resonance. Here, I think the science is not great. It's not exactly wrong, but there is no solid explanation or definition of resonance given which gives the impression that the examples cited are two distinct types of resonance. I think I would show this video to my class after our resonance discussion and ask them what they like and don't like about the video.

There are more videos, but they are all demonstrations of the artifacts shown in the above videos. See the playlist here:

Finally, if you want to see more about the devices shown in the videos, there is information on the museum's website.

August 19, 2016

All my students are getting a book on learning this term

From this past summer's physics teacher camp website, I caught this excellent list of readings on teaching and learning:

There was a bit of overlap between this list and a series of articles, infographics and other material that I have compiled into a booklet I am affectionately calling the “Book of Infinite Learning”.  The learning is what is infinite; the book is not.

I compiled all the articles together and printed them in booklet form.  Of course, I have no rights to these articles, so I can't share the books beyond my classroom, but I can share the links to the articles that went into this booklet.
Here’s a partial list of all the articles I’m giving my classes this Fall:

  1. How Does the Brain Learn Best? Smart Studying Strategies -
    This article is from the Mindshift blog on KQED’s website.
  2. The art of back-of-the-envelope calculations -
    From FermiLab’s Symmetry Magazine.
  3. Bigger Gains for Students Who Don’t Get Help Solving Problems -
    Another article from the Mindshift blog.
  4. What It Feels Like to Be Bad at Math -
    This article is from the incredibly brilliant Math with Bad Drawings blog.  Check it out!
  5. Failures, Mistakes and Other Learning Tools -
    This is a post from the Adventures with the Lower Level blog. It really spoke to me when I first read it.
  6. Learning goes through The Land of Confusion -
    Great short piece by Rhett Allain.
  7. The Key to Science (and Life) Is Being Wrong -
    From one of the Scientific American blogs.
  8. Multitasking while studying: Divided attention and technological gadgets impair learning and memory -
    An article from Slate.
  9. The Big Lie About Student Achievement -
    From Huffington Post.
  10. Telling You the Answer Isn't the Answer -
    Another piece by Rhett Allain.
  11. Two Common Misconceptions About Learning -
    Yet another piece on learning by Rhett Allain.
  12. Confuse Students to Help Them Learn -
    This piece is from The Chronicle of Higher Education. It highlights Derek Muller’s physics education research work.
  13. How ‘Deprogramming’ Kids From How to ‘Do School’ Could Improve Learning -
    Another piece from the Mindshift blog.
  14. Re-reading is inefficient. Here are 8 tips for studying smarter. -
    From  Out of the 8 tips, there are a couple I don’t fully agree with, but the others are really good. The article as a whole is a great discussion starter.
  15. O Adjunct! My Adjunct! -
    From The New Yorker.  Our students need to know about precariat faculty.
As you can see, I have a few favorite sources that I have drawn from over the years - Rhett Allain and the Mindshift blog, especially.  All the articles are things that others have shared with me on twitter over the years.  I'm always excited to get to share them with students - bring on this new term!

February 07, 2016

What is wrong with “What is up with Noises?”?

I have two disclaimers about this post.  First, this post is coming about four and a half years late. What can I say? I'm not so good at the internet hot take thing.  The second disclaimer is that I wrote these notes up quickly today while dealing with a teething and sick baby.  These are my quickly-jotted notes.

Alright, so here's the deal - in late summer 2011, Vi Hart posted the following video about the mathematics and physics of sound:

I've said it before, and I'll say it again: I like Vi Hart's videos. She has great enthusiasm for math, science and music. Her passion is wonderful. But this video was not great, in my opinion. There are a number of mistakes that she makes and misconceptions that she perpetuates. I think there was a bit of criticism when the video first came out, but it was mostly about how she wrote "vasilar" membrane instead of basilar membrane. She edited the description of the video to say "Accuracy not guaranteed."  That doesn't really stop people from watching the video - not that I want to deter people from getting excited about sound and acoustics at all.  But it's a bit frustrating when there are so many mistakes in such a popular video.

So, below are my notes on the video.  There are parts that I like, and I mention them as well.

1.) 0:02

Talks about air molecules set into motion by the strings and then the wave reaching your ear. But the strings don’t move nearly enough air to make a sound that is audible. The string drives the bridge, which drives the top plate of the instrument.  Much of the sound radiation comes from the top plate, but the top plate also drives the air inside the cavity as well as coupling to the back plate.

2.) 0:37

She conflates speed and frequency which is a common misconception.  Strictly speaking, not WRONG, but poor phrasing since the speed of the string depends on what point on the string you are looking at as well as the amplitude and the speed is constantly changing.  The frequency is not changing (as much). I really don’t like when people use this type of phrasing, since it perpetuates misunderstandings of frequency.

3.) 0:40-50

The initial description of the swing is not bad, but it is not used as completely as it could be, and as we’ll see later, the analogy is stretched beyond what is accurate.

4.) 0:55

Says “That’s amplification.”  Well, actually, what was described was resonance, but that was not mentioned. 

5.) 1:02

While it is true that driving an oscillator at a frequency above it’s natural frequency will not result in an amplitude as high as if it is drive at the natural frequency (which is what resonance is) you aren’t technically dampening the vibration in that case.  That is a nit pick, I guess. However, the visual in the video doesn’t exactly match what is being described, either.  

6.) 1:08

"(The string) wants to swing at a certain speed, frequency.” - Again, the conflation of speed and frequency.  This bothers me because when you look at the wave speed and the relation between wave speed, frequency, and wavelength it is something different than talking about frequency using the word “speed”.

7.) 1:19

It’s not called a sympathy vibration - it’s called a sympathetic vibration.

8.) 1:22 - 2:26

The description of how the ear works is overall not too bad. 

Weirdly, at 1:29 there is a "Fun Fact" in the video which says the number of molecules in a sound wave is larger than the national debt.  I can't even unwrap what that is supposed to mean.  I get that the sentiment is that there are a large number of air molecules involved in the transport of sound, but - the units are different and how is this "sound wave" defined so that we can count the number of air molecules?

9.) 1:47 

“faster frequency” should be “higher frequency” so as not to reinforce the speed = frequency misconception.

10:) 2:38 - 3:07

This whole mess of talking about pushing the swing every other time is just bizarre.  The idea that you can drive an oscillator at a lower frequency and then get it to oscillate at it’s natural frequency is inherently non-linear when applied to acoustics-related oscillators. I’m not even really sure what it says about the physics of a pendulum, to be honest.  And this is not to say that there is NOT any non-linear effects at play in the ear or with the production of sound, but for what is discussed in the video, the nonlinearities are insignificant.

11.) 3:08 - 3:30

In this section Vi is applying non-linear behavior to the motion of the basilar membrane. She asks: if one frequency goes in, shouldn’t the cochlea respond at places where  I’m not actually an expert on the auditory system, but I have never heard about non-linear effects in the cochlea for pure tones at normal sound levels. I’d love to know if I’m wrong about that, but I don’t think I am.

12.) 3:30 - 3:46

Vi asks a really interesting question here. She asks if your ear hears a complex sound at a certain fundamental frequency f, but then a second complex sound at frequency 2f is played, wouldn’t your brain perceive them as the same even if they came from different places?  At least, that is what I understood her to be asking.  If so, that is a great question!

13.) 3:48 - 5:25

She does a good job of introducing the idea of the overtone series here.

14.) 5:26 

"…this is not some magic relationship between mathematical ratios and consonant intervals. It’s that these notes sound good to our ear because our ears hear them together in every vibration that reaches the cochlea."

She is starting to tie the ideas of the overtone series back to her question posed at 3:46.  As stated, the above quote is TRUE for the example that she gave (or any overtone series, really).  My issue with what is stated is that it makes it sound like ANY vibration that reaches our cochlea has the overtone series embedded in it, which is not true.

15.) 5:34

“Every single note has the major chord secretly contained within it."

This statement is true only if the note is a complex tone containing a harmonic spectrum, which is often the case, but not all instruments will produce such notes.

16.) 5:48

Finishes the explanation of the overtone series.

17.)  5:50

“…because of physics, but I don’t know why…”  This is just annoying.  Much of the previous explanation contained a lot of physics.  There’s no excuse to just say “I don’t understand physics…"

18.) 5:54

“…twice as fast…” Again with the frequency / speed issue.

19.) 6:25

“You don’t notice the higher (harmonics), usually, because the lowest pitch is loudest and subsumes them."

The lowest frequency in a harmonic spectrum is referred to as the fundamental frequency. The fundamental frequency often, but not always, has the highest amplitude in the spectrum. But your ear still associates the PITCH of the sound with the fundamental frequency whether it is loudest or not - or even there at all, as the video points out later.  Note that this line also incorrectly uses the term “pitch” to refer to a component of the complex tone.  Pitch is a subjective quantity that you associate with the tone as a whole.  (So, if we’re counting that is 2 errors here.)

20.) 6:51

“String is pushing around the air…"

Same mistake as made at the start of the video: the string is not pushing a large amount of air. The top plate of the viola is doing the pushing on the air molecules of the sound wave that you hear.

21.) “Basilar membrane is vibrating in sympathy with all these frequencies…"

I’m not sure that it is wrong to say the basilar membrane is vibrating in sympathy with the other parts of the ear and air and instrument, but I’m not sure it’s correct to say it is vibrating in sympathy with the frequencies. Call this a minor nitpick. 

22.)  7:14

Description of timbre is brief, but good.

23.) 7:17

Compares the sound a pure tone makes to the vowel sound “ooh” and says it sounds like a flute. Timbre is a subjective quality of sound, but I would disagree that all pure tones sound like oohs or like a flute.

24.) 7:27

There is a comment here about using our mouth to “shape the overtones coming from our vocal cords”.  I’ll grant some poetic license to this statement, and it is true that the mouth shape helps determine the vowel sounds. It would have been better to include all parts of the vocal tract. 

25.) 7:33 - 7:50

The lowpass filter demo - it’s not exactly clear to me what concept is being demonstrated here.

26.) 7:54 - 9:42

Overall this section is not bad. I will point out that when overtones are played separately and then together you are cuing your ear to listen to the different parts of the tone, and so many people (certainly not everyone, though) will be able to pick out the different parts of the tone after being cued. That does not make the tone any less of a complex tone, but you need to be careful what conclusions you are drawing from this demo.  Also, she did not control for amplitude in the overtones starting from about 8:07 and so every combination of tones is clipped, meaning that the sound coming from the speakers actually has MORE harmonic content in it than she intended to demonstrate.  This can be seen graphically in the waveform at 9:41.

(I’m going to ignore the overtone fitting the number of bumps comments around 8:45.) Her idea to show the waveforms in actual size is pretty neat, I think.

27.) 9:43

"To make this shape, it pushes forward fast here, then does this wiggly thing, and then another big push forward."

Another reference to “fast” and the rest of the description is not physically or mathematically great here.

28.) 10:20

“Some frequencies get pushed the wrong direction sometimes…”  I don’t even know what this means. Frequencies aren’t getting pushed anywhere.  This makes no sense to me.

29.) 10:25 - 11:16

The parts about the sound source discrimination are pretty good.

30.) 11:17-11:50

The part about the missing fundamental is good. 

31.) 11:52 - end

I think Vi does a great job of reminding us that there is a lot of beauty and wonder in nature that science and mathematics can help us explore.  I’m certain that this joy she brings to her videos is what keeps people sharing and watching them.