| Topic: |
Science > Physics |
| User: |
"qwerty" |
| Date: |
29 Sep 2005 10:05:10 AM |
| Object: |
Can someone idiotproof this for me |
I am trying to explain SR to my brother - again.
I think I will use the Doppler Shift to explain it.
postulate 1 of SR : all inertial reference frames are the same. ie an
experiment in one will give the same result as an experiment in the
other
postulate 2 of SR: the speed of light will always be measured the same
in any inertial reference frame
I have a car with a red light at the back emitting light at 700 nm.
scientist1 and scientist2 are passengers and each has a device for
measuring the wavelength of the light.
The car is driven at 30 m/s and scientist1 measures the wavelength of
the light.
He measures 700 nm. The car is stopped and scientist1 again repeats the
expirement and again gets 700 nm. This demonstrates the first postulate
of SR.
Scientist2 also gets the same results.
scientist1 then gets out and stands at the side of the road.
The van is then driven towards him at 10,000 m/s (its a thought
experiment ! )
scientist2 inside the van measures the wavelength and measures 700 nm
as before. he has another device for measuring frequency and the
frequency he measures is 4.254 x 10 ^ 14 hertz.
he does a calculation and gets a speed of light of 2.98 x 10 ^ 8 m/s
scientist1 however measures a slightly shorter wavelength caused by the
doppler shift (ive already explained this for sound using a siren on
the van) .
he also measures a slightly higher frequency, doing his calculations he
too gets a value for c of 2.98 x 10 ^8 m/s
@@@@@@@@@@@@@@@@@@@@
i am sure ive made a howler at the end by referring to the doppler
effect.
.
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| User: "Timo Nieminen" |
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| Title: Re: Can someone idiotproof this for me |
30 Sep 2005 02:06:27 PM |
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On Fri, 30 Sep 2005 wrote:
Timo Nieminen <timo@physics.uq.edu.au> writes:
The funny part is that one shipment had a largeish carton in it that was
surprisingly heavy. When I picked it up, I thought "this feels like
Alberts". Generic box, rather than a single-title box. Open it up, and
look. Inside was a complete single-title box of Alberts, with about 1cm of
packing around it.
Now, why would somebody do that? To make it heavier yet?
I don't think 1cm of packing and an extra box made any significant
difference. I can't guess why, beyond the generic reason of "stupidity".
I used to train people to pack books in boxes (so they could do this when
I wasn't there, since I was part-time). This wasn't too difficult,
usually, but I did find one person (who was a uni student, as were almost
all of the part-time employees there) who I could train. How can somebody
get into a university if they can't be taught how to pack books in boxes?
It might have been that that made stupidity cease to surprise me.
Advanced students have different needs. I tell them that Jackson is a good
investment; they'll stil be learning from it in 10 years time. OTOH, this
is also a reflection on the difficulty of learning from the book ...
I had Jackson with me in a dugout in Sinai, for half a year.
Not long enough to exhaust the book, I assume?
Not quite, but I made good progress (and learned some humility in the
process).
Are you (or any other reader) familiar with Van Bladel's book? It was
mentioned to me that it's a good book, intermediate in crypticity and
completeness between Jackson and Landau & Lifshitz. I see that Wiley is
bringing out a new edition.
<rant>
Why, oh why, does Jackson grind through electrostatics and magnetostatics
first, and put the real beginning in the middle of the book? Not that
that's such a big deal, since grad students should be capable of turning
to the middle of the book ... But the stuff on Fresnel reflection
coefficients? Ack! It's the perfect opportunity to present a nice simple
1D case of pruning of general solutions to the vector Helmholtz equation
through boundary conditions and orthogonality of wavefunctions over said
boundary, and it's all theta, theta', theta''. What are you going to do if
it's a lossy/gainy dielectric? Complex angles? (Well, apparently some
people like it that way, but not me.) Such an icky presentation of what
should be the simplest example of practical use of general solutions from
separation of variables.
Of course, when I did it the way I think it should be done, my students
didn't understand me either. Well, at least not without effort and pain.
(Wot? No learning without effort and pain? Is the "gimme" culture really
without foundation? Heh, heh, NMP!
</rant>
--
Timo Nieminen - Home page: http://www.physics.uq.edu.au/people/nieminen/
E-prints: http://eprint.uq.edu.au/view/person/Nieminen,_Timo_A..html
Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html
.
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| User: "Timo Nieminen" |
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| Title: Re: Can someone idiotproof this for me |
30 Sep 2005 12:08:35 AM |
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On Thu, 29 Sep 2005 wrote:
I really think that it is a matter of creating the impression that
they get enough for their money. "What, $60 for this textbook, that's
outrageous!" "Now, now, consider, you're getting 12 lb worth of
knowledge for your money, at 5 bucks a pound it is dirt cheap":-)
Back when I was a student, I worked at a textbook store. Among other
things, I got to process incoming stock. The heaviest carton of a single
title was Alberts "The Cell" - it might have only been 8 to a box, but it
was thick, and apparently printed on extra-dense paper. About 30kg/carton,
iirc. (Of course, the publishers would say that when packing returns,
don't exceed 20kg (or 15kg, depending on the publisher) per box, but
they're happy to send us 30 kg monsters.)
The funny part is that one shipment had a largeish carton in it that was
surprisingly heavy. When I picked it up, I thought "this feels like
Alberts". Generic box, rather than a single-title box. Open it up, and
look. Inside was a complete single-title box of Alberts, with about 1cm of
packing around it.
Advanced students have different needs. I tell them that Jackson is a good
investment; they'll stil be learning from it in 10 years time. OTOH, this
is also a reflection on the difficulty of learning from the book ...
I had Jackson with me in a dugout in Sinai, for half a year.
Not long enough to exhaust the book, I assume?
--
Timo Nieminen - Home page: http://www.physics.uq.edu.au/people/nieminen/
E-prints: http://eprint.uq.edu.au/view/person/Nieminen,_Timo_A..html
Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html
.
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| User: "Timo Nieminen" |
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| Title: Re: Can someone idiotproof this for me |
29 Sep 2005 05:08:43 PM |
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On Thu, 29 Sep 2005 wrote:
Timo Nieminen <timo@physics.uq.edu.au> writes:
Students, OTOH, like 1 page books (reading, at any rate, if not buying). 1
down, 499 to go!
That much is true. But, as you say, they don't like paying for books.
I tell my 1st year students (actually, it's a bridging course, high school
physics in 12 hours of lectures for those who didn;t do it in high school)
something along the lines of:
1) They might want to have a textbook to complement the lectures
2) I don't recommend any specific textbook; in the past I have, and
some students have liked the recommended book, and others have not.
3) If they're going to do another 1st year physics course, the book for
that one will do fine
4) The best book is the one they like to read
5) The best book is the one they understand best
6) The library has about 12 linear metres of shelf space of generic
physics books; borrow one. At the very least, go there and browse and see
which one you like.
7) Here are some www links to free physics books. No/inadequate
connection? - a CD will get you a bunch of freely redistributable books.
Given the money that's poured into generic 1st year physics textbooks by
publishers, I'm a little surprised that there are so few good ones. OK,
there are lot's of reasonable ones, reasonably correct, easy enough to
read, comprehensive enough. But they're (mostly) so immensely thick! What
student wants to read a kpage? It's not buying the book that's necessarily
the issue, but reading the thing! A clear and concise 300-500 page
textbook might be just thing I'd tell my students to buy.
At least one publisher is now offering a cut-down 700-or-so page textbook;
I should get a copy for evaluation. OTOH, maybe I should just set "Cartoon
Guide to Physics" as a required text.
Advanced students have different needs. I tell them that Jackson is a good
investment; they'll stil be learning from it in 10 years time. OTOH, this
is also a reflection on the difficulty of learning from the book ...
</rant>
--
Timo Nieminen - Home page: http://www.physics.uq.edu.au/people/nieminen/
E-prints: http://eprint.uq.edu.au/view/person/Nieminen,_Timo_A..html
Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html
.
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| User: "Androcles Androcles@ MyPlace.org" |
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| Title: Re: Can someone idiotproof this for me |
29 Sep 2005 07:16:30 PM |
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"Timo Nieminen" <timo@physics.uq.edu.au> wrote in message
news:Pine.LNX.4.50.0509300757460.28959-100000@localhost...
| On Thu, 29 Sep 2005 wrote:
|
| > Timo Nieminen <timo@physics.uq.edu.au> writes:
| > >
| > >Students, OTOH, like 1 page books (reading, at any rate, if not
buying). 1
| > >down, 499 to go!
| > >
| > That much is true. But, as you say, they don't like paying for
books.
|
| I tell my 1st year students
/rant
Oh... you are a teacher... that explains your fuckwittery.
Androcles.
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