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 -  http://bit.ly/brain-learn-best
    This article is from the Mindshift blog on KQED’s website.
  2. The art of back-of-the-envelope calculations -  http://bit.ly/back-of-envelope
    From FermiLab’s Symmetry Magazine.
  3. Bigger Gains for Students Who Don’t Get Help Solving Problems - http://bit.ly/bigger-gains
    Another article from the Mindshift blog.
  4. What It Feels Like to Be Bad at Math - http://bit.ly/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 - http://bit.ly/failures-mistakes
    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 - http://bit.ly/land-of-confusion
    Great short piece by Rhett Allain.
  7. The Key to Science (and Life) Is Being Wrong - http://bit.ly/key-to-science
    From one of the Scientific American blogs.
  8. Multitasking while studying: Divided attention and technological gadgets impair learning and memory - http://bit.ly/divided-attention
    An article from Slate.
  9. The Big Lie About Student Achievement - http://bit.ly/big-lie
    From Huffington Post.
  10. Telling You the Answer Isn't the Answer - http://bit.ly/rhett-telling
    Another piece by Rhett Allain.
  11. Two Common Misconceptions About Learning - http://bit.ly/learning-misconceptions
    Yet another piece on learning by Rhett Allain.
  12. Confuse Students to Help Them Learn - http://bit.ly/confuse-students
    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 - http://bit.ly/deprogramming-kids
    Another piece from the Mindshift blog.
  14. Re-reading is inefficient. Here are 8 tips for studying smarter. - http://bit.ly/studyingsmarter
    From Vox.com.  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! - http://bit.ly/o-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.





November 17, 2015

On incentives in the classroom

This article from NPR was passed around in my social networks quite a bit last week: How To Get Students To Stop Using Their Cellphones In Class The meat of the article is contained in the following excerpt (my emphasis added in bold):
Ten percent of the grade in his class comes from participation points. Students get points by answering a question when called on, by asking a good question or by responding to a poll. (Duncan uses clickers, devices that allow students to collectively answer multiple-choice questions in class.)

For his experiment, he says he got buy-in from students first, as he wrote:

"I asked them to vote if I should offer one participation point for taking out their cell phone, turning it off and leaving it out on my desk. To my amazement the vote was unanimous. 100% voted yes. So they all took out their phones, put them on the desk, and we had an exceptionally engaged class."
I tend to view my classes a bit like an economist: students will respond to whatever incentives we provide them with. If we provide them with the incentive of easy points, most will choose to take whatever action is necessary to get the easy points.

In the case of Duncan's class, the incentive is a point in exchange for placing a turned-off cellphone on a desk in the front of the room.  It's not clear what that one participation point each class contributes to the total of a student's overall grade.  It is reasonable to conclude that the one point will not translate into making or breaking any student's grade for the term. The hope is that the commensurate increase in engagement (due to removal of distraction) is an overall larger effect on the students. That is, a more engaged student will gain in the subject knowledge more than just whatever the one participation is worth in the weighted score.

I don't use participation points because I want to incentivize the learning of the content of the course. I don't want students to be counting points through the semester, because if they do that, then they are not focusing on the concepts we spend all of class discussing. I have gotten rid of all points in the classes I teach, opting instead for ratings in a standards-based assessment and reporting approach. It has worked well, and I believe I am helping students be intentional about thinking about the concepts in order to get the grades that they want.

But, I struggle with the students who choose to get their cell phones out and ignore what we are doing in class. I then have to wonder: what if I have the wrong view of incentives?  What if Duncan is providing a small and conceptually meaningless incentive in exchange for getting higher conceptual gains?  Is that a better approach?

I don't have answers for those questions.  I just hope I'm not completely wrong with what I'm already doing.