This works for both light and sound, because both are different kinds of waves. Sound waves are in air; light waves are in empty space.
I'm proud that my textbook will be probably the first ever in which the generic figure of a human being looking at something from the side is a woman. My thanks to Andrea, who was working in the office across the hall when I needed a picture. Yes, I do most of my own artwork: I also do all my own stunts, my department chair hates it.
If I were to proclaim to the world that I'd spent 45 minutes and still couldn't figure out what an iambic pentameter was, or what a sonnet or a minuet were, you'd probably think I shouldn't be proud of it. The Doppler effect is simpler than any of these.
It's not "just" a Jeopardy question, either: exercising students' ability to think in this way can have practical value. I didn't get back to post until late on Monday night because, while on the way to an Intro Astronomy lab, I had a blowout. I know, those aren't supposed to happen anymore, but it did: silly university vehicle. I engaged my rational mind, got the manual out of the glove compartment, turned to the section on how to use the jack, fixed the tire, and got to lab on time, anyway.
Cool! and very clear. I'm still not sure *why* shorter/compressed waves are bluer and longer/stretched ones are redder, but I suspect that doesn't matter, as long as they consistently are, since the consistent pattern allows the observer to figure out which way an object is moving.
ReplyDeleteThat IS a pretty good image. I totally understand it now.
ReplyDeleteCassandra. It's because blue light is a shorter wave length than red light. Think about the visual light spectrum with more distance between the waves on the red end and less distance between them on the blue end.
ReplyDeleteAnd yes I'm a humanities person so if I have a completely wrong understanding of this someone please tell me so I don't make other people ignorant based on my confidence.
@Natalie: You're doing fine. I should have also posted the picture of the light waves: the red one has a long wavelength, or distance between waves, the blue one has a short wavelength, and I put a green one of intermediate wavelength in between, to show that all the other colors are in between.
ReplyDelete@Natalie & Frod: actually, I get that part. I was just wondering whether there is a reason *why* the longer wavelength produces what we call red, while the shorter one produces what we call blue (and the medium one produces green). But I suspect that might get into a circular argument/explanation.
ReplyDeleteThis will blow my pseudoanonymity with my friends who read this, but.... You know how everything in physics is a point or a sphere? We had a saying about "spherical cows" and "spherical chickens". so the Spherical Chicken became the department mascot. We had the department t-shirts made up with a blue spherical chicken on the front and a red spherical chicken on the back. It cracked us up. We thought it cracked everyone up. Everyone else was just laughing at us.
ReplyDeletejesus h, Frod, you're really getting off on the Doppler stuff. Shout it from the rooftops!!!! DOPPLER!!!! DOPPLER!!!!!!!!! I LOVE DOPPLER!!!!!!!!!!!!
ReplyDeleteI'm proud of you. Educate the hell out of those sons of bitches.
:-)
Wombat, i would have laughed at the shirt and not at the person wearing it. But I'm a science geek hiding in humanities geek clothing.
ReplyDelete@Cassandra: See Eye and Brain, by Richard Gregory. Long-wavelength light triggers red receptors in the retina, and blue-wavelength light triggers blue receptors, much as in an ordinary digital camera. Still, the exact chemical processes that do this in the retina are unclear. If we knew this, we might be able to cure color blindness with drugs.
ReplyDeleteWe also don't understand how this triggers the areas of the brain that perceive color. Medical imaging such as fMRI scanning is showing which areas of the brain are involved, but we still don't understand much about how the brain works. There is lots of evidence that different people see and perceive color very differently, but little understanding of why: Eye and Brain discusses this. We understand even less about why the mind says, "How beautiful!" when it becomes aware of color.
@Wombat: You left out my favorites, fractals.
sorry, but here is a gender neutral doppler diagram
ReplyDeletehttp://whs.wsd.wednet.edu/Faculty/Busse/MathHomePage/busseclasses/apphysics/studyguides/chapter15_2008/Chapter15StudyGuide2008.html
and she's wearing a dress
My favourite bumper sticker (on a red car): "If this car looks blue, you're driving too fast."
ReplyDeleteWombat - Anyone who was laughing at you was not a person whose opinion need concern you. Anyone worth anything desperately wanted one of those shirts.
ReplyDeleteAlso, I want one of those shirts!
Frod: "If we knew this, we might be able to cure color blindness with drugs."
ReplyDeleteOnce on LSD, I saw infrared. Ordinary color blindness would be no problem.
Frod, thank you for the clear, concise, and complete explanation. However, you delivered it with many a rhetorical eye-roll, which was my point originally -- that saying "it's not all that hard, you know" to someone genuinely trying to understand something is insulting, and I heard that enough from male science teachers that I quit the sciences flat.
ReplyDeleteThere is no such thing as "an iambic pentameter." There is just iambic pentameter. Do you know why it's used so frequently in Anglophone poetry? Do you know what's the most frequent opening move of a poem in iambic pentameter? Do you understand the difference between accentual and syllabic poetry? Could you scan a poem for us as well as a literature Ph.D.? Do you know a triolet when you meet up with one? Because honestly, people have their areas of expertise, and the rest tends to become a bit of a blur if you don't study it after 10th grade or college or whatever. You could be more humane about that.
However, I love that your observer is not only female, but wearing pants and of normal weight rather than a Betty Boop silhouette. So I finish with a warm heart for you, Frod.
Aww Frod, I knew I liked you! You're a compulsive explainer like me!
ReplyDeleteFrod: "If we knew this, we might be able to cure color blindness with drugs."
Probably not drugs actually, as the cause of most color blindness is a defective gene on the X chromosome (hence the greater prevalence among men)
Once gene therapy gets worked out, then you can fix it by inserting a functional copy of the gene without having to understand the exact physics of the photoreceptor.
I have to ask....
ReplyDeleteand I'm really not kidding...
What about the part where you treat light as particles instead of waves? Doesn't that change the observer/observed thing relationship?
In case you couldn't tell:
my gig isn't in physics:-)
Dear Froderick,
ReplyDeletePlease write to NPR with a similarly brilliant diagram and ask them to stop talking about cooling REACTORS when, in fact, what is being cooled are SPENT FUEL RODS.
XO,
The Hound
I apologize for the tortured grammar in that earlier comment. I need coffee.
ReplyDeleteBlackDog,
ReplyDeleteYou don't want to know what torture they're doing to the language when they talk about plate techtonics. Though my one (and believe me it is only one) fun science fact out of that entire mess is that the northern part of Japan is on the North American Plate.
On the other side of things, has anyone looked at the amazon reviews of the secondary literature about nuclear accidents? There is a totally bizarre string of defensive comments left by people claiming to have been at the actual accidents (Idaho Falls and Three Mile Island). They attack the author if he or she isn't a nuclear engineer, in the one case that the author is both a trained historian and a nuclear engineer they attack the his nuclear training.
The same thing doesn't appear in the public reviews of the Chernobyl literature. I can't decide if that's because no one wants to defend how that reactor was managed. Or there is no one alive to complain.
Two weeks ago I was trying to pitch a research idea about the origins of a particular kind of nuclear accident response and was told it was too out of left field. Sometimes I really hate what I chose to study.
Okay, so, while we're in this impromptu physics class:
ReplyDeleteWhat happens when (1) the object emitting waves remains STATIONARY relative to its waves, such that the circles are concentric, BUT (2) the observer is moving toward the emitter?
It seems that this would also create a Doppler effect, since more waves will pass the observer per unit of time (meaning greater frequency). Yet every source I can find describes the Doppler effect strictly in terms of a moving EMITTER.
Does relativity, with that "speed of light is constant in all inertial frames" stuff, prevent the frequency of light passing an observer from increasing?
What about other waves, such as sound? Will the pitch of a stationary siren go up as you move toward it?
Yes, the effect is symmetric to inertial observers. An observer moving faster enough towards a red light will see it turn green (try that out on the cops). Extra credit: can you measure a velocity greater than the speed of light from the Doppler effect?
ReplyDeleteHonest_prof.
ReplyDeleteNo.
Frod, they'll never in a million years let you use your own art in the textbook.
ReplyDeletethank you. I am amazed how much science I have learned on this blog. well, OK, only a little, but still this diagram makes it very clear.....
ReplyDeleteLurking scientist here. Yes, the effect is present and the same whether the emitter is moving and the observer is stationary or the observer is moving and the emitter is stationary. It only depends on the relative motion between the two. Whence the term _relativity_. Yes, the pitch of a siren (or car horn) changes if it is stationary and you drive by it. This is an easy observation to make on the highway if you are paying attention when it happens. The Doppler effect also remains if you treat the light emission as composed of particles (photons) rather than waves, but in this case, the math is more difficult, and we build it in to the way we perform the calculations. That usually is upper-level physics major math or beginning graduate work. But the effect is the same.
ReplyDeleteThe theory of Special Relativity says that the speed of light is the same for all observers (caveat), and the consequence of this is that the concept of events occurring at definite times is no longer valid. Different observers in relative motion to one another will see things happening at different times. It seems very weird and spooky, but it is true. If it were not, your GPS system would not work the way it does.
Back to the original post, it is a shame that some students get squicked out by relativity or the way that Nature sometimes defies what we might think of as common sense, and yet that is the way the world works. But we see this all the time -- students resist these complicated ideas because they cannot un-learn the things that they think they "know".
And I also think that educated people should have some familiarity with basic and advanced math skills and should be familiar with general science concepts like the Doppler effect or photosynthesis.
"It's really not that complicated" - Frod, could you be more condescending? (Yes, that was a rhetorical question. Here are some more.)
ReplyDeleteDo you really think I'm "proud" I don't understand this? Do you really think repeating over and over how simple / basic / common-sense / general knowledge a concept is does anything but tear down a student (or another misery-dweller) who can't wrap their head around it? If I can't understand something so "simple", what does that do to my self-esteem? If I hear those messages constantly, how does that impact my desire to learn? Haven't we all had to exorcise someone's voice from our head at one point or another because their message that we suck (at math, at sports, at ballet, at relationships, at whatever) was/is just bullshit holding us back? Does any of us really want to be that voice for someone else?
Like many "gifted" people, I also have learning difficulties. Like many "gifted" people, this took a very long time for anyone to figure out - because I was obviously so "smart", if I was doing poorly in a subject, it meant I was "lazy" or "not trying".
Not every student is like me - but some of them almost certainly are. And we're not "resisting complicated ideas", we're drowning in them while trying desperately to understand them, feeling shittier and shittier about ourselves with each failure, hearing your voice in our heads asking us why we "can't get something so simple" - because even if you've never said that to us in words, we can tell you're thinking it from your tone and your attitude.
I'm in position now where I can call you on your crap - I'm a fully functioning adult, and I have the academic credentials to back up my claim to not being an idiot or a slacker. I also have a substantial (theoretical and lived) understanding of how race, class, gender, sex, and able-bodiedness (among other interlocking factors) impact what is considered to be valid / essential knowledge, how it's taught, and who is considered qualified to do the teaching.
So please, and I mean this sincerely and without malice, check your privilege and your assumptions - and try to teach in a way that builds people up instead of tearing them down.
Thank you.
(PS: To those who have accused me of really being "drunk" in the past, my handle is a lyric from a Leonard Cohen song. The man's a genius. Google it.)
Drunk,
ReplyDeleteI certainly see why you would take it this way, but please don't. It's not directed at you or anyone here. But, hard as it is to believe, there ARE people who are proud at not grasping the basics of math and science. They are and when they meet us they practically gloat "Oh, GAWD, PHYSICS?!!! I [hated/sucked at/couldn't get] physics!!" Frod was venting about that. Not you. Not anyone here. The people who DO feel pride at being bad at something on the same level as non-math-science stuff we'd be treated like ignorant assholes for not getting. And while I agree with F&T that he came off condescending, when we don't get it, that's exactly how the other side sounds to us.
-WOTC
@Wombat:
ReplyDeleteThanks, but...
"If I were to proclaim to the world that I'd spent 45 minutes and still couldn't figure out what an iambic pentameter was, or what a sonnet or a minuet were, you'd probably think I shouldn't be proud of it. The Doppler effect is simpler than any of these." (quoted from Frod's post above) seems like it's speaking directly to my post on the earlier thread, where I said "After reading your post, I've just spent the last 45 minutes researching the Doppler Effect (and yes, going to peer-reviewed sources and not just the dread Wikipedia) - and I have to tell you, I don't understand it either." (full post/context on the March 13 Sunday Thirsty post.)
Sure, educated people should have basic math and science. Educated people should also have a basic knowledge of world history, literature in their own language and in translation from other languages, geography, and an ability to read, write and speak comprehensibly in at least one language besides their own. Educated people should also be able to think critically and distinguish good arguments from bad ones.
ReplyDeleteI don't see any reason to privilege any one of these.
I can't stop myself from getting involved in this just a little. I think Merely Academic's note above makes sense, but what I reject is the (not stated, but I think implied) notion that being educated is somehow better than the alternative.
ReplyDeleteNow, of course I'm not saying that a populace of complete nincompoops is ideal, but I can't tell you how many unhappy nights I've spent - as an academic - surrounded by educated people.
Doesn't anyone sometimes HATE being around colleagues and other academics? It wears me out.
Most of my real pals - real world pals - are certainly smart, but not educated in the way I think it's being used in this series of comments.
My closest pal is a guy who manages a mid-sized garage in my town. If I told him that I thought an educated person should have a basic knowledge....blah blah blah, he'd tousle my hair - or what's left of it - and say, "Fuck that."
And then we'd go to a hockey game and eat too many of the $2 hot dogs.
Wow, Drunk, tell it like it is. Thank you.
ReplyDeleteAnd I've probably told this story before, but once I had a student in a comp. class whom I secretly took to be a grinning fool, a good-looking class clown type who seemed to ooze self-confidence despite his having sub-par skills. He came to my office, much to my surprise, for some help. As I spoke, he asked for the definitions of words I was using. I thought he was mocking me, but answered straightforwardly, and he unzipped his backpack, took out a stack of index cards, and wrote down the word and the explanation for each one on a separate card. I asked him why he did that. And he said this: "My dad beat the crap out of me so I really only have about an eighth-grade education, because the rest of the time I was just trying to survive. So I have a lot of catching up to do, and this is one way I do it." I worked, and worked, and worked with this kid on his writing. He wasn't stupid, but he had enormous deficits, and getting him to a C was a challenge.
Since then I have understood that attitude can be self-defense, that even the students who turn me off the most have a story.
@F&T: You make my heart melt. May I be your colleague?
ReplyDeleteFrod, I'm with you. The diagram makes the concept perfectly clear to me and I previously had no idea what it was. While I don't understand it well enough to ask you complicated questions like those upthread, I get the general idea. I don't know why your student did not, I suppose that's the big question from your previous post. It doesn't matter if she's dumber than a box of rocks or a gifted savant; the bottom line is that she can't learn and that's a problem for a college student. Unless she's an otherwise decent student who simply can't grasp the Doppler Effect? If so, just let it ride or keep trying to teach her the Doppler Effect; those are your two choices.
ReplyDeleteAnd I also think that educated people should have some familiarity with basic and advanced math skills and should be familiar with general science concepts like the Doppler effect or photosynthesis.
I agree, and I'm not giving science more precedence than iambic pentameter, just that, despite best efforts upthread, Frod's student is struggling with science, not English (or at least, not so far as we can tell in Frod's tale)
As far as being an "educated person," I strive towards that, but the process is far from complete. There was a gap in my knowledge shaped like the Doppler Effect, and now it's been patched up. Thanks, Frod. Also, science is hot! I hope all you science de-lurkers stick around.