Fullerton

Inbound Brown Line

Cat sleeps on litterbox box

This cat has multiple soft places to lounge which were purchased specifically for her. She prefers the cardboard the litter box came in.

First day of winter quarter

This desk won't stay clear for long.

First day of winter quarter

This desk won't stay clear for long.

Toy Camera effect

at Caribou for coffee

R wins 364-331

Renae won today. I got all the high value tiles, but she got the only bingo: refront.

R wins 364-331

Renae won today. I got all the high value tiles, but she got the only bingo: refront.

Running track lengths

Yesterday, Rhett at Dot Physics had a comment about last week's puzzler on Car Talk.  He had an alternate solution to the question about how a pair of people could walk side by side for an hour and cover different distances.  His solution was that they were walking on a circular track. (Read his solution for a full explanation.)

At the end of the post he said:

It doesn’t even have to be a circle – it can be just curved at the ends and straight in the middle. Of course in this case, the husband would have to slow down on the straight parts (or the wife would have to speed up) in order for them to stay side by side. But it could be done.

There was something about this that didn't seem right.  I remember the track I used to jog on had one lane that was 8 laps for a mile.  Let's use that as the lane for the husband in our example.

Here's the layout of the track:

Let's use Rhett's values for the inner and outer radii: 4 m and 5 m, respectively. If the outer track is an 1/8th of a mile, then how long are the straight sections?

1/8th of a mile is about 200 m. The circumference of the curved part of the outer track is d = 2×π×5 m = 31.4 m. So the length of each straight section for the outer track is 84.9 m. 

The circumference of the curved part for the inner track is d = 2×π×4 m = 25.1 m. But the length of the straight sections is the same.  So the total length of the inner track is 25.1 m + 2 × 84.9 m = 194.9 m.

The wife has to walk 33 laps to go 4 miles. If the husband and wife are walking side-by-side the whole way, he also walks 33 laps.  His lane was 1/8th of a mile, so he has gone 4 miles, plus an extra 1/8th.

I still like Dot Physics.

Results are in

Over the weekend, I was watching the Mythbusters episode which was testing the idiom "It's like taking candy from a baby."  The phrase is used to imply that something is as easy as, well, taking candy from a baby. But long ago, I realized that phrase makes no sense at all. Anyone who's every been around babies knows that if a baby wants something, then even if you can easily take it from them, what you're really going to have is whatever you took away plus an unhappy baby. If the something you are taking away is candy, then you're likely to get tears from the baby, too. So taking away candy from a baby is just mean.  I think that's a better representation of the idiom.  What said you on the poll?

Clearly, most people went with the traditional meaning.  The three "other" responses all included meanness or cruelty in some way.  Still, most people (3:1 from this non-scientific poll) seem to think it is easy and not that mean or cruel to take candy from a baby. 

What can you do with this?

I just wrote this up over at the home.drewsday blog, but the real reason for taking the photos was to use this in class next quarter. We start with thermodynamics; one of the first topics is thermal expansion and contraction.

I regularly read Dan Meyer's blog. He was (is?) a math teacher, but I'm consistently inspired by his ideas. One of his regular features is something he calls "What can you do with this?" [WCYDWT]. The idea is that he finds an example of something in the world which illustrates a math concept and brings it into the classroom.

When I saw the contraction of the vinyl siding on my house, I knew I could bring it into the class next quarter.  The question is: What can you do with it?

I want to present this to class, so I have to think of the questions that would be appropriate.  Usually, when I start a problem in class I make a list of everything I know and everything I don't know (or want to know).

What I know

• temperature outside today was 12° F. ( T_i )
• nominal length of the siding was 12 feet. ( L₀ )
• change of length (on one side) was 1/8 inch. ( ΔL )

What I don't know (would like to know)

• temperature when the siding was painted ( T_f )
• coefficient of linear expansion for the vinyl siding (α)

Relevant equation

• ΔL = αL₀ΔT

The problem is that I have two unknowns (ΔT and α).

I have no idea what the temperature was when the house was painted. I didn't even know the house existed when it was painted.  I suppose I could come up with a reasonable estimate, but realistically, there is a pretty wide range of temperatures to work with. Conservatively, I would guess that the painting could have been done when the siding was anywhere between 60° F and 90° F. That is a pretty wide range, so I'm not sure I want to try to estimate that and use it to find α.  So let's make the initial temperature something we want to find. 


This means that I need to figure out what the coefficient of linear expansion is for the siding. In class we discuss how the thermal expansion process is approximately linear over a certain range. I have no idea if the expansion of vinyl siding is linear or not.  I'm going to cross my fingers and assume it's linear-ish. 


With a bit of googling, I learned that vinyl siding is made of unplasticized polyvinyl chloride (uPVC). I also found the coefficient of linear expansion is listed as 50 ×10^-6 °C^-1 for PVC. I couldn't find uPVC thermal coefficient, but every listed coefficient I could find was close to this value. 


Using that thermal expansion coefficient, and solving for the initial temperature, I found that the initial temperature was 23.6° C, which is 74.5° F.  (Right in the middle of my estimated range, hmmm...)


I think that the value for the coefficient is reasonable.  I plan to work this example in class, then extend it by asking the class to calculate what the maximum expansion/contraction range would be for a 12' length of siding in Illinois weather.  I'll be looking for other ways to extend this. 


Side notes:

1. The units specified online for the coefficient of thermal expansion are often given as [L]/[L][T] (e.g. m/mK). Of course, the length units cancel and all that remains is inverse temperature units, which is how our textbook lists the units.
2. Coefficients of linear expansion for common materials varied quite a bit (sorry, not scientifically quantified) from one table to another. Surprisingly, the PVC coefficient seemed to always be within 2% of 50 ×10^-6 °C^-1.

I'm curious, so I'm setting up this poll...

Loudness and sound pressure levels

This morning the blogs and twitter feeds were linking all over the place to a passive amplifier for your iPhone. (See it here: Science & Sons OS v1.0)

The idea behind a passive amplifier is that it requires no electrical power to increase the amplitude of the sound wave which is presented to your ear. Just pop your iphone into the cradle and crank up the tunes. As long as the battery in the iphone is charged, you have amplified sound.

It sounded cool, so I checked it out. This is what caught my eye:

The Phonofone III is an elegantly designed passive amplifier crafted from ceramic and designed explicitly for iPhone. This clever device amplifies the volume emited from an iPhone internal speaker roughly 4x (approx. 60 decibels).

Wait. What? I get a 60 dB gain out of a device with no power?  Let's see if that passes the sanity check. I don't have an iphone, but I have heard the iphone playing audio from its internal speaker. Unamplified, at a moderate level, I would say the sound level observed from an ipod (at an average distance) is about the same as the sound level of a typical conversation.  Let's look at what the approximate sound level would be:

(I found this chart on OSHA's website. I assume the image is public domain, like most government images.)  From the chart you can see that conversation at 1 m is approximately 60 dB(A).  (The "A" means A-weighted, which is a weighting factor used to approximate the frequency response of the human ear.)   Let's be conservative and estimate the iphone unamplified level to be about 55 dB. That means that if I drop the iphone into the passive device the sound level should be 55 dB + 60 dB = 115 dB.  That's louder than the "Discotheque" rating in the chart (when/where was this chart generated?) which is also about 20 dB louder than a jackhammer at 15 meters.  Somehow I really doubt that the single horn + iphone is going to be able to compete with the speakers and amplifier of a dance club.

What about the other claim?  They say the sound will be about 4x louder.  Here's where the claim might hold some water. The basic idea of a horn is to provide better impedance matching  between the driver and the sound field and to control directivity of the sound radiation.  Assuming the horn is pointing at an observer, the sound level at the observers ears should be higher with the horn than without the horn.

What if their claim that using the horn causes a perceived 4x increase in loudness is true?  (Loudness is a perceptual quantity, where sound level - either sound pressure level or sound intensity level - is a measured quantity.)    Then, the only mistake that they made is equating a 4x increase in loudness with a 60 dB gain in sound level.  Here's a graph from a lab we do in my "Sound and Acoustics" class:

In this lab students hear a broadband tone which they assign an arbitrary loudness level rating. In this class, we all agreed to call the reference tone (relative sound level = 0 dB) a loudness level of 100.  Note, there are no units, since it's an arbitrary scale we made up for the lab. Then they hear several other tones where the level has been increased or decreased randomly and they are asked to rate the loudness of the tone with respect to the loudness of the reference tone.  

What I've plotted above is the class average of loudness level vs the actual relative sound level (in dB) for all trials.  Each sample was presented twice (not in sequential order) so the scatter is a sort of approximation to the uncertainty in the measurement.  The solid line represents a model that is what we would expect to see for a larger sample of the population.  For such a small class, the trend is pretty close to the "expected" behavior.

Note that a 4x increase in loudness, from either 25 to 100 or 100 to 400, corresponds to a relative gain in sound level of 20 dB, not 60 dB.

Under ideal testing circumstances, I could believe that a passive amplifier like the horn amp would give a 20 dB gain right in front of the horn.  But someone should have caught the 4x = 60 dB nonsense.

A side project...

Moving into our first house that we own, I thought it would be fun to try to document all the home-improvement (and maintenance) projects that we undertake.

Obviously, that means I must blog.

I'm announcing today the home.drewsday blog.  This is where I am documenting everything that we do in the new house.  Hope you like it!

Do what I do, not what I say

One of the things that I decided to do based on recent classes I've taught is to try to reinforce the importance of students reading the material before coming to class.  To that end, I decided to implement reading quizzes due every morning that class meets.  But I also want to have walked in my students shoes as much as possible, so I have decided to read every section that I've assigned to them and take notes like I want them to be doing.

It may seem obvious to do this for every class, and certainly when I've taught the upper level courses I read and re-read (and sometimes re-re-read) all the sections we cover.  But for introductory classes I find that to prepare I generally need only skim over the chapter to see what topics are being presented and in what order.  Then, I have enough to worry about with prepping demonstrations, clicker questions, homework problems, in-class tutorials and anything else I can think of to help cover the topic in an active-learning classroom to have a lot of time to actually read the whole chapter.  Starting early, though I hope to get far enough ahead that I can finish all the reading assignments before the end of the quarter.

The reading quizzes are going to have two questions which will be the same each time, and then one or two additional questions which will be unique for each quiz.  The questions which repeat are: "What are two important concepts that you learned from the reading?" and "What are two concepts from the reading which you struggled to understand?"

I plan to use these questions to guide my note-taking as I read the book.

School is starting soon

Yesterday, a bunch of colleges and schools started up for the year.  Our campus is on the quarter system, so I still have a few weeks left to prepare.  My browser has become cluttered up with education-related articles that I've been saving up to comment on, but I think I'll just dump them out here.

A conversation with Sean Carroll - in this NY Times interview from April, I was a little disappointed to read this response from Sean:

Whenever you say you’re a physicist, there’s a certain fraction of people who immediately go, “Oh, I hated physics in high school.” That’s because of the terrible influence of high school physics. Because of it, most people think physics is all about inclined planes and force-vector diagrams. One of the tragedies of our educational system is that we’ve taken this incredibly interesting subject — how the universe works — and made it boring.

I get what he's saying.  But I'm disappointed that he would paint all high school physics teachers with such a broad brush.  I believe that at some level, ALL physics teachers got into teaching physics because they found the subject to be terribly interesting.  What about giving them the tools and motivation to make their classes interesting?  What about structuring schools so that biology teachers are not teaching physics?  These are complex questions that the interview does not get into.

His response to the follow-up question which was about what he would do to improve physics education was a little better in spirit, but I think it's a little unrealistic to think that starting with the Big Bang and particle physics is something that will lead to better scientific literacy.

No grading, more learning - This was an article from "Inside Higher Ed" that I found via Metafilter. A professor at Duke dispensed completely with the traditional method of grading (where the professor assigns grades for work turned in) and chose to "crowdsource" the grading.   The class as a whole (I guess) assessed whether or not student work met the standards for the course.  The discussion on Metafilter rightly pointed out that many classes have cliques of students which professors may or may not be aware of.  I am impressed with how this professor was able to turn the focus of the class away from the grades and onto the learning.  I am, however, not deaf to the concerns raised by many of the commenters talking about this method.  I don't think this would work for my courses where almost everything we do is a "right-or-wrong" type of assignment.  Still, it was interesting and inspiring to see faculty get their students to focus on learning.

Does Professor Quality Matter? -  You should read this article (from the Journal of Political Economy) to get the whole story, but I'm just going to skip to the end and quote from the conclusion:

Our findings show that introductory calculus professors significantly affect student achievement in both the contemporaneous course being taught and the follow‐on related curriculum. However, these methodologies yield very different conclusions regarding which professors are measured as high quality, depending on the outcome of interest used. We find that less experienced and less qualified professors produce students who perform significantly better in the contemporaneous course being taught, whereas more experienced and highly qualified professors produce students who perform better in the follow‐on related curriculum.

I'm not sure how much to read into this as it relates to teaching physics, but it was a somewhat interesting article.

Cory Doctorow: What I do - Not education related, but if you're a nerd who follows Cory Doctorow, now you can do what he does.

You say up, I say yesterday - This is a great profile of a cognitive psychologist who has studied a fascinating topic of how language relates to thinking.  I was really blown away by these ideas. (Cog psy is ALMOST as cool as physics...)

Plan B: skip college - This NY Times piece doesn't say anything that hasn't already been said about whether or not college is the best economic choice for all people.  But, it is a good reminder that we (as a society) should constantly be questioning how ALL people can best be served by education at all levels.

What if College Tenure Dies? - A series of essays in the NY Times opinion section.  Really good, thought-provoking stuff here.

Tenure, RIP -  Closer to my heart (and life), though, was this article in the Chronicle of Higher Ed. about how the percent of tenure-track positions available across the country has shrunk dramatically in the past few decades.  I don't have the time to go fully into what I really think about this situation, but from a personal level, I would just be THRILLED if I could get offered some version of a permanent job.

This press release talking about a research project connecting a poem by Walt Whitman with a meteor shower caught my eye.  The research was cool, but I LOVED the interview with the student research assistant:

...get involved and be as active and connected with whatever department and professors they have. That's been the most beneficial thing to me. Once you start talking to your professors and meeting with your professors and they realize that you're a real human with a brain and you're interested and excited they'll do anything for you, and you'll do anything for them. With that, find someone -- it doesn't matter who it is or what department they're in -- find a professor and make a connection...Also, fear can get you down. That's why I didn't want to be a physics major [initially], because I was afraid I couldn't do it. Don't be afraid of boys, don't be afraid of professors -- once you get over that you can do anything.

The part about "Don't be afraid of boys" was because the question was about advice to give to other female physics majors.  But, I just found her overall attitude throughout the whole interview to be great. She has everything that every faculty member is looking for.

Hanny and the Mystery of the Voorweep - New graphic novel about the discovery of a weird astronomical object.

The Hot Young Teacher they Hired Instead - Along with the Tenure, RIP article, this sort of struck a personal nerve, simply by being about the hiring process in education and the pain that a teacher goes through.

Hot for the Wrong Teachers - This article from Slate is about 2 years old, but it was new to me.  This gets into some of the reforms that have been implemented at one school in NYC.  There is also a discussion of proposed ideas and what is and is not working currently.

Whew!  I had more stocked up than I had realized.

The usefullness of solution sets

I'm teaching a intensive introductory physics course this month. We cover a quarter of intro physics (algebra based) over a 3 week span. I have been handing out problem sets every day, which students work on every other day in recitation-style sessions.  None of the problems are graded, although the students are strongly encouraged to complete all the problems as part of studying for quizzes and exams.

I was a little surprised to learn that the instructor for the previous course (I'm teaching the middle course) provided complete solution sets to the students. It's not something I had planned to do. So on the first day of class, I was asked if there would be solutions provided.  I agreed to try posting solutions to the course Blackboard page.  Of course, this meant writing out solutions in addition to preparing for the next day. Since I had only written down the answers to the first set and needed to prepare the second set, I posted the answers to the first set and the solutions to half of the second set. By today, I was ready to post a full solution set to third set of problems.

I thought I was being generous.

Generally, I would not provide a solution set to a class.  I believe that students develop a false sense of security by relying on having solutions for all their problems.  Because, eventually I will give them an exam. And there will be no solutions for them. It's a bit like someone learning to ride a bike using training wheels.  You don't go from always using training wheels one day to entering a bike race the next day.

But a few of my students gave some clear reasons why they wanted full solutions.  The reasons ranged from "sometimes I don't know how to start the problem" to "if I'm getting the wrong answer, I can use them to check my work" and everything in between.  So, I'm going to try to post as many solutions as possible.  We'll see how it goes.

Popcorn soup!

Popcorn soup!

End of term clean-up.

Today I'm in my office to clean up and get ready for the summer term course I'll be teaching in July. I've got a stack of papers to go through, clear off my desk and dump in the shred bin. But, I've also got a collection of science news stories which have been cluttering up my browser. In the spirit of clean-up, here's a small link dump:

• PhD student in Canada is studying the psychology of earworms. (What's an earworm?)
• Another Canadian psychologist has examined how Rembrandt draws viewers into his paintings.
• An engineering student in England has adapted a bike to pump water in Guatemala.
• NASA's Mars Reconnaissance Orbiter flew over the Phoenix lander and may have imaged the damage to the lander, explaining why it never woke up after the Martian winter. 
• Infrared image of nebula from the WISE telescope looks like a pair of hearts situated next to each other in space.
• Want to go to Neptune and come back in 5 years?  It will only cost you $4 trillion. (More links at bottom of that page.)
• Possibly the most adorably unfortunate misspelling of hadron ever.  Let's hope this kid never loses his interest in science. 
• Something hit Jupiter last year, and amateur astronomers saw it first.
• In May, The Big Picture featured a round-up of really great images of Saturn and its moons.

I think that is all the links I've been saving up. You can always see my shared google reader links, even if you aren't following me.

Back to clearing the desk.

A tourist in our own town...

These are some ideas for places to visit in and around Chicago this summer when we have visitors and/or free time to go exploring.

If you are coming to visit us, or if you have any opinions on these places, let me know what you think of them.