Subject: Re: Temperature, Pressure, and Humidity
From: Alan \"Uncle Al\" Schwartz
Date: 18 Nov 1996 16:18:24 GMT
tieleman_bill@timeplex.com (Bill Tieleman) wrote:
>I have a burning question regarding a simple matter of checking the
>accuracy of a hygrometer to be used - of all places - in a humidor.
>
>I have been led to understand that placing the hygrometer in a closed
>container with damp salt, should - once stabilized - result in a reading
>of 75% relative humidity. After much jacking around, I found this to be
>true. The science is lost on me, but I'd really appreciate if you of
>true scientific bent could elucidate on a few salient points...
A saturated salt solution (e.g., everything which can dissolve has
dissolved, and there is still solid remaining) will have a constant vapor
pressure at a constant pressure. (Said pressure depends upon the
chemical identity of the salt, and has a >very< weak dependence upon the
state of subdivision of the solid as you walk toward micrometer and
nanometer dispersions.)
>1) Does the temperature inside the test chamber matter?
Absolutely (heh, heh). The higher the temp the higher the vapor pressure
(Clapeyron equation).
>2) Must the temperature remain constant during the test period?
The reading will depend upon the temp only at the time of measurement,
assuming equilibrium of phase and instrument.
>3) How long should the test system take to stabilize?
> - two tbsp. of salt in a small plastic cup
> - twelve drops of water
> - double sealed inside two gallon size ziplock bags
Give it 24 hours. You might throw in a little more water as long as
solid remains. Unless there is forced air convection or other means of
gas phase mixing, the chamber can only equlibrate by diffusion.
--
Alan "Uncle Al" Schwartz
UncleAl0@ix.netcom.com ("zero" before @)
http://www.ultra.net.au/~wisby/uncleal.htm
(Toxic URL! Unsafe for children, Democrats, and most mammals)
"Quis custodiet ipsos custodes?" The Net!
Subject: Re: Time & space, still (was: Hermeneutics ...)
From: moggin@mindspring.com (moggin)
Date: 18 Nov 1996 18:30:04 GMT
Mati:
>> It may influence a person to get involved in
>>>science, in the first place, in may influence the choice which area of
>>>science to pursue and what kind of approaches to consider. Scientists
>>>aren't problem solving machines and they're often influenced by
>>>extrascientific factors in their thinking. This is all part of the
>>>"scaffolding of science". But, I'll repeat it again, the final
>>>product stands or falls on its own, with total disregard to the
>>>ideology of the author (in fact with total disregard to the identity
>>>of the author).
moggin
>> Repeat it as often as you like -- it was never at issue. We were
>>discussing whether or not religion played a role in science -- you
>>seem to have conceded that it does, so the rest is moot. One small
>>note -- the product never "stands or falls on its own," but only in
>>the eyes of other scientists, who are, as we now appear to agree,
>>liable to be influenced in various ways.
virdy@pogo.den.mmc.com (Mahipal Singh Virdy)
>Look moggin, you can take away food and shelter from practicing
>scientists and that too will _influence_ the Science they practice. You
>can torture them and their family to death and that too will influence
>what they _claim_ to think. Or, you can love them and worship them and
>give them fancy cars and homes and paid vacations etcetra and that will
>also influence them. Get it? If not, reread the damn paragraph.
Are you disagreeing with me? I'm having a hard time seeing
where.
>If you
>still *refuse* to get it, here's some advice. Remove sci.physics from
>the header and say whatever the explicative your brand of religions and
>philosophies want to hear. I doubt if many *actual* physicists would be
>bothered by what you say about Science then. It's just the way
>partitioning of the newsgroups works. We'll *all* deal with it.
While here it's unclear what you're saying, if anything.
moggin:
>>Instead you've chanted your mantra: "Does it work or doesn't it?"
>>That's beside the point, as I've said,
Mati:
>As you've wrongly said, since this is exactly the point of science.
>You seem to have a great dislike to this notion, but it is there
>nevertheless.
moggin:
>> You don't have any idea what I think about it, since I haven't said a
>>thing on the subject. That's because it's irrelevant to the issue you
>>raised -- namely whether any significant part of physics was based
>>on religious mysticism. Now you claim that you meant to talk about
>>something else: how science judges ideas. You're so confused, that
>>may be true -- but asking, "Does it work or not?" merely tells you
>>(hold onto your hat) whether or not a given concept "works" -- it
>>doesn't inform you of the nature of the idea, or of its provenance.
Mahipal:
>Believe it or not, moggin you are finally beginning to make some sense.
That's one of us, then.
>At least, your motivations are something tangible however misguided.
>Don't claim I don't know what your motivations are! How can I --- you
>haven't stated them! Like Duh!
Actually, the problem here is that _you_ haven't stated them, so I
can't either agree or disagree with your assessment.
>I contend that you are incapable of
>expressing anything wrt your motivations though you harbour a malicious
>intent on passing judgement on those that disagree with you --- down to
>the damned typing mistakes. Yep.
Wrong on the facts -- I've never attacked anyone for making a typo.
(I'd better not, either, considering what a crappy typist I am.) And as
I've pointed out before, my judgements here have been directed mostly
at people who agree with me, but see fit to attack me, nonetheless --
really, though, they've already passed judgement on themselves.
>Yes, DAMN IT, scientists are people too. Like duh! Yes they get
>influenced by all forms of human endeavours. Sure, we're all connected.
>Fine. Who gives a Dime --- or pairs of.
That's another discussion -- I agree that it's unimportant in the
context of this one. That's why Mati shouldn't have brought it up,
in the first place, and why I offered only a small note in reply.
>Did "religious mysticism"
>influence Newton's or any other scientist's thoughts? Does it matter to
>what they consequently discovered? Can you see the difference between
>those two questions?
Yep. Can you see the connection? (That's just something to reflect
on -- no need to tell me your answer.)
> The terms "pragmatic" "utilitarian" escape your
>comprehension? It seems to me you just want to argue for argument's sake
>--- the classic annoying pointless philosphers who can't get that the
>pope really did shit in the woods.
Oh, I see -- you're another member of the scientific illiterati.
>LET THE SCIENTISTS TELL THE PHILOSOPHERS AND RELIGION-guys WHAT SCIENCE
>IS! Is that too unreasonable a request? God, this is the twentieth
>century isn't it? Is it too late to get off the planet for me? ;-)
This is a whole 'nother subject, but yes, it's unreasonable. May I
suggest we skip the much-too-obvious argument that's staring us in
the face?
>The force/influence of Religions and Philosophies is entirely too damned
>real. Hell, the Religionists and Philosophers won't STOP demanding that
>they never be ignored. We're all too painfully aware of Obviousisms. Now
>try comprehend this: Scientific Laws are completely and unequivocally
>independent of the personal beliefs of the Scientists who discover them.
>Fine, now you'll claim THAT in itself is a philosophy.
No, I'll claim it's irrelevant. Apparently you want to have one of
those tired, old debates over "scientific objectivity." I'm not biting.
>Like so what?
>It's not a trivial philosophy. It's falsifiable. It's testable.
Really, I'm not letting you drag me into this. But those ideas
are part of the philosophy you want to defend -- not tests of it.
>It's an
>idea which has physical manifestations and demonstrates itself to be
>true in all physical "E"xistence.
Do you think so?
>Now do you want to proclaim that
>Philosophy is Physics? I doubt it. You are so repulsed by the success of
>science as the center of intellectual thought this close to the
>millennium that it burns your soul --- provided you have one. Oh yeah,
>Religions can't prove you have a soul! Err... religions must be wrong.
You've lapsed back into incoherence -- just thought you'd like
to know.
>Grow up. Limitless rhetoric does not a contribution to intelligence make.
As you've nicely demonstrated.
-- moggin
Subject: Re: what causes gravity? (remedial)
From: pstowe@ix.netcom.com(Paul Stowe)
Date: 18 Nov 1996 18:34:21 GMT
adona26963@aol.com wrote:
correction...the warp of "spacetime" would be more accurate
and I don't think it very circular to say that mass does this
depending on its density and locality.
As used in the literature, space is a defined coordinate system
consisting of three orthogonal axes (dimensions) and is explicitly
devoid of physical properties. We therefore can have a unique
coordinate definition for all points (x,y,z) throughout the region.
"Space-Time" imposes a t coordinate for every x,y,z where, for each
x,y,z,t, t maps from zero to infinity providing the ability to describe
physical changes at each spacial point through this dimension (time).
However, and this is very important, this coordinate structure is only
a conceptual/mathematical construct, and, in and of itself has no
physical properties. So the question remains, what constitutes the
"warp" of spacetime.
Now given we can use space-time as a framework in which to
describe physical properties, but this does not allow us to magical
endow it with physical properties.
The point is that gravitation is the effect of "interacting"
forms of matter on itself within a local framework. If it is
necessary to gain a clear view of the picture by stepping
back, as is often the case rather than stepping forward, then
the whole region of spacetime as we can perceive or observe
it (no small difference b/w the two) is filled with matter, so
it must be "interacting" all at once; rather at several (or
more) "once"s- hence space"time". It is of my opinion that
taking a step back helps to see the picture better, as
spacetime "gravitation" or "matter" fields unique at each
space and time, yet I know of an equation or set that could
allow us to translate one event between two frames. Is that
what the Lorentz transformation and the Minkowski
spacetime uses for analysis of frameworks of "spacelike,
timelike, and lightlike" events? So it is not meaningless to
say (to me at least) that gravity is the manifestation (rather
than force-...
Now let's see what such renowned references such as Condon &
Odishaw's "Handbook of Physics" says about the matter.
In Section 2, chapter 6, subsection 28 [page 2-50] titled "The
Physical Model of Space-Time:
"...The physical model starts from the hypothesis that for the study
of general characteristics of space-time structure it is sufficient to
consider matter and radiation as smoothed into a kind of perfect fluid
whose most important characteristic is its energy distribution ..."
and below in subsection 29, titled "The Perfect Fluid" we see:
"The theory used to describe the perfect fluid in the general theory
of relativity is a direct extension of that of classical hydrodynamics
and its reformulation in the special theory. The fluid is assumed to
be characterized by the physical properties of pressure p and mass
density rho. ..."
So we see that GR is described as a fluid dynamical model that
maps the physical properties of pressure and density onto the
coordinate system x,y,z,t. This process explicitly assigns physical
properties to the term space-time.
Now "warp" make sense as a pressure gradient (which results in a
velocity gradient [i.e an acceleration field]). However, by
definition, an acceleration field in the presence of, and acting on
masses, results in forces. A "null geodesic" is is simply an isobar
within this model. In the absence of velocity changes, a mass moving
with velocity v in an vector direction not parallel to the velocity
vector (defined by material body M) sqrt[2GM/r] results in a direction
descibed by vector summation (a curved path). Does this mean that this
is not force related, no it is simply a result of and a balance in said
forces.
... it seems almost anything rather than a force) of the
tendency (property) of matter, in a given "region" of
spacetime, to create interaction fields unique to each of many
possible observation locales with ways to translate, rotate
about the axis, etc. what one frame of reference sees to
another frame of reference. It may help the reader to point
out that I am now writing while considering the effects and
importance of gravity in general terms from no formal
training (yet) while thinking of larger systems (like the
universe- always a great lab) rather than sub-atomic particles
and their interactions. I say this because although I didn't
mention them before, there probably are many clues to a
future or modified gravitation theory in quarks, leptons,
gluons and so forth. With a bit of concentration, one can
easily see the misleading nature of calling atomic particles
the cause of gravity because they are the components of
matter. If the electro- magnetic force (which I am not suspect
of but do not fully integrate into a newer GR just yet without
revising, even post-QED) is just like the gravitational "force"
then (hopefully you've heard this before) WHY IS GRAVITY
ATTRACTIVE while proton neutron and electrons repel and
attract? I'm not saying that in order to be a force it has to
repel also, but gravity is, in my opinion, either a special
force, the true nature of which has been elusive but MUST
be simple (theoretically it could be complex, although
complex systems can/should be summarized simply to be
effective-- E=mc2 = "light speed unity/constant,
space & time relative to observer....time dilation, length
contraction... folks, this is REAL" and still some people don't
believe A.E., they don't get it...., "they" didn't like G.G. or
N.C.either.)
6. GRAVITY, or Gravitation, is not a force but a
geometrically extractable entity ,identical in effect to such
force, of the matter which is percieved to have such "force"-
all in the context of a four-dimensional spacetime (for
purposes of convenient analysis- e.g. transformation, rotation,
etc). It may be easier or more natural for others to just think
of it as a force but I don't believe it is. Or at least its a
special one (due to its relationship with matter, energy, space,
and time) and deserves special attention, not a preexisting
theory (Theory of force?) which can explain gravity, in its
own terms and not those of so elusive a topic, as a force.
WHAT GOES UP.....MUST.......
uhhh......what goes UP?
Simply put, take away the physical properties space-time and the
whole idea of "warpage of space-time" collapses. Assign physcial
properties to space-time and you have physical medium by simply
another name. This fact was not lost on Einstein, who when
discussing this specific topic said:
"Recapitulating, we may say that according to the general theory of
relativity space is endowed with physical qualities; in this sense,
therefore, there exists an ether. According to general relativity
space without ether is unthinkable."
"Sidelights on Relativity", Dover Publication, page 23
Paul Stowe
Subject: Re: How Much Math? (not enough)
From: C369801@mizzou1.missouri.edu (Walker on Earth)
Date: Mon, 18 Nov 96 12:00:36 CST
In article <328E1180.C8F1FF@Physik.Uni-Muenchen.de>
"Ralf A. Engeldinger" writes:
>Walker on Earth wrote:
>>
>> My
>> own intuitive powers find little challenge explaining the lack of a
>> net gravitational force at the exact center of a spherical shell, for
>> example, but they could in no way ferret out the supposition that the
>> net force is also zero anywhere else inside as well :-(
>
>My shot at this: From rotational symmetry it follows that the
>tangential component of the force anywhere inside vanishes and that
>the modulus of the radial component depends only on the distance from
>the center. Now, moving from a point with non-vanishing radial force
Agreed.
>component at distance r from the center straight through it to the point
>at the same distance on the opposite side one would obviously cross a
>point with non-vanishing divergence of the force field (in
>non-mathematical terms this is a point where a field line begins or
>ends). Since non-vanishing divergence of the field means non-vanishing
>mass density we have a contradiction. Thus the radial force component
>vanishes everywhere inside.
>
>Does this count as "intuitive?"
Well, if it works for you . . . :-) Now that you've pointed it out,
that is yet another 'intuitive' way seeing that the net gravitational
force is zero everywhere inside the shell. Me, I've always been
partial to the area squared subtended by an angle just compensates
for the square of the distance argument - a strongly geometrical
one.
It's interesting to see what one counts as intuitive and what one
does not, and how, from the few examples already displayed, the
extent of one's physical intuition is strongly dependent their
mathematical background . . . to bring this back to the original
topic. For example, I'll go out on a limb and say the symmetry
argument showing the lack of tangential forces inside a sphere,
requires no mathematics, and thus should be intuitive for every-
body, but the 'intuitive' line of reasoning you give for the
absence of radial forces as well cannot be characterized as such
unless you already know something about divergence.
Any other good examples, like say Gaussian surfaces for electrostatics?
Subject: Re: Polywater
From: billb@eskimo.com (William Beaty)
Date: Mon, 18 Nov 1996 19:01:33 GMT
Michael Fullerton (cmatrix@spots.ab.ca) wrote:
: Jim Rogers <"jfr"@[RemoveThis/NoJunkMail]fc.hp.com> wrote:
: >To be fair, Michael, you really must know that "cold fusion" in this
: >context is the Pons and Fleischman variety, and *not* Muon Fusion.
: Sorry, I do not "really know" this. Huizenga still looks like a
: slack-jawed drooling crackpot since he has never presented any factual
: or even logical evidence (surviving simple scrutiny) that the Pons
: Fleischman Effect is in any way in the same league as N-rays and the
: like. Like all raving crackpots, science and logic is against him.
Recent news: CETI is now selling "Cold Fusion" research kits, including
training in how to avoid pitfalls in replication. These are based on
Palladium thin films on ceramic beads, and use light OR heavy water
electrochemistry. They are intended for researchers interested in the
subject. They are optimized to produced transmutation rather than excess
heat, so purchasers will need access to SIMS, auger probe, etc., to
analyze the "ash" produced by the claimed reaction. The price is
somewhere around $4,000. I don't have the url for CETI right here, but
it's on my CF webpage at
http://www.eskimo.com/~billb/weird/wcf.html
--
....................uuuu / oo \ uuuu........,.............................
William Beaty voice:206-781-3320 bbs:206-789-0775 cserv:71241,3623
EE/Programmer/Science exhibit designer http://www.eskimo.com/~billb/
Seattle, WA 98117 billb@eskimo.com SCIENCE HOBBYIST web page
Subject: Re: Universal Coordinate System
From: Darrin Edwards
Date: Mon, 18 Nov 1996 18:13:21 GMT
odessey2@ix.netcom.com(Allen Meisner) writes:
> How about, if the laser is attached to the buoy? Is it improper to
> say that if the buoy is at absolute rest, then it is an absolute
> reference frame? [...]
> Regards,
> Edward Meisner
Well, I can't think of any way I could defend claiming your statement was
"improper". But that's a very big "if". Aren't we trying to figure out
whether we can say that the buoy is at "absolute" rest or not?
This is the third time I've asked this question, so I'll try not to ask
it again (I'll assume it's either a stupid question, or I'm just not
capable of wording it in anything other than an obscure way):
If observer 1 (measuring his coordinates by buoy 1) thinks he is at rest
(no deflection of laser at buoy 1);
and if observer 2 (measuring his coordinates by buoy 2) thinks he is at
rest (no deflection of laser at buoy 2);
and if everyone, including observers 1 and 2, agrees that observer 1
is moving at a constant velocity with respect to observer 2, and that
observer 2 is moving at a constant velocity with respect to observer 1,
then how do you decide which, if either, of observers 1 and 2 is "really"
at rest (at "absolute" rest)?
("Everyone" above of course means everyone in inertial frames... People
who live in accelerating frames shouldn't throw stones at glass houses,
or something like that...)
Cheers,
Darrin
Subject: Re: How Can 16 Waves Out of Phase Be Added?
From: breed@HARLIE.ee.cornell.edu (Bryan W. Reed)
Date: 18 Nov 1996 19:13:55 GMT
In article , David Kaufman wrote:
> I need to know how to add 16 (or more) out of phase
>waves to find their resulting energy on a vibrating atom.
>Would anyone please show how this is done?
>
> When I add 2 waves, I'm combining 2 different distances
>of 2 mechanical waves travelling in the same medium. If I
>new what distance to use for this combined wave, than I
>imagine I could add another wave to it, and then be faced
>with the problem of what resultant distance to use to
>combine the next wave, and so on.
>
You either assume linearity and simply add the effects of all the waves
(which is what's usually done), or you consider nonlinear effects
perturbatively (so that the interaction of two waves produces a couple
of other waves of much lower amplitude, and so on), or you solve a messy
nonlinear problem on a computer. Generally in a solid the displacement
from equilibrium of each atom is much smaller than either the inter-
atomic spacing or the wavelength of the disturbance, so you can just
add the displacements from each individual wave, to good approximation.
You use the "unperturbed" position of each atom in the formula (the position
it had when there were no waves).
Have fun,
breed
Subject: Re: Sophistry 103 (was: I know that!)
From: meron@cars3.uchicago.edu
Date: Mon, 18 Nov 1996 18:55:11 GMT
In article <56pdho$q94@news.ox.ac.uk>, patrick@gryphon.psych.ox.ac.uk (Patrick Juola) writes:
... snip...
>Okay. First of all, you're not, since you don't even understand
>the terms "mapping" and "relation" as used in standard mathematical
>parlance. Second, I'll try to bring you up to speed here.
>
>A relation is simply an association between elements of one set (the
>domain) with another (the range). There's no necessity that this be
>1-1 in either direction; I can, in the general case, associate any
>or all domain elements with any or all range elements, either
>individually or by subsets (since the power set of a set is
>simply a set itself). An easy example of a relation is the relation
>between a person and his/her senator -- easy because it's nice and
>intuitive, and also not 1-1. Every US citizen has two senators (usually),
>every senator has a whole slew of contituents.
>
>The nice thing about sets is that they handily blur the singular/multiple
>distinction. Instead of dealing with the relation between a senator
>and his constituent as indiviual linkages, I can simply take the set
>of the constituents and build a new relation between the senator and
>the *set* (formal mathematicians have terms for this sort of stuff; I'm
>simply blurring it here.)
>
>Now, the first thing that I would like to point out is that the set,
>itself, is non-sensible; there's no measurable property of set-ness that
>distinguishes the "set" from the collection of its elements, but it's
>certainly reasonable to talk about "the citizens of New Jersey" as a
>unit. I suggest that the burden of proof is on *you* to demonstrate
>that the non-sensible "thing" that is the "set" described above doesn't
>exist. Similarly, what is this thing called "you" distinct from the
>individuated atoms that compose it?
>
>The second thing I would like to point out is that, as I stated before,
>the use of this sort of power-set construction blurs the distinction
>between singular and plural in a very definite direction -- I can
>treat a multiple object as a singular for purposes of
>association/reference, but not the opposite.
>
>So -- non-sensible objects exist; the test of whether or not a set
>can be discussed meaningfully is not a question of existence, but
>whether the concept of the set is shared between two partners in
>communication. The fact that words carry multiple meanings and that
>people can have multiple intents is not a problem, since one can simply
>bundle these things into sets and take the representation relationship
>accordingly. Now, if you want to try telling me that you're qualified
>to discuss these sorts of points, go ahead. I'm already expecting
>flamage from Mr. Meron about how badly I oversimplified to the point
>of lying.
Oh no, not at all. Given the background of the audience in this case
I'm not sure that an oversimplification is even possible.
Carry on :-)
Mati Meron | "When you argue with a fool,
meron@cars.uchicago.edu | chances are he is doing just the same"
Subject: Re: What is a constant? (was: Sophistry 103)
From: meron@cars3.uchicago.edu
Date: Mon, 18 Nov 1996 20:59:24 GMT
In article , moggin@mindspring.com (moggin) writes:
>
... snip ...
>
>Mati:
>
>>And you still don't see the difference between the last one and your
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>>statement "Newton was wrong". My, my, I guess I overestimated your
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>>intelligence.
>
>moggin:
>
>: I made my point clear. You agreed with it several different times --
>:nonetheless, you continued to dispute it with me -- for weeks on end!
>:That leads me to the comment I offered above. Although there must also
>:be other factors, and probably more interesting ones.
>
>Mati:
>
>>I asked you a clear question.
>
> You asked no questions, clear or otherwise. Feeling confused again?
It really doesn't take much intelligence to realize that the
underlined text above is a question.
>
>Mati:
>
>>What is the difference between "Newton was wrong" and "the belief that
>>Newton's theory is universally valid was proven wrong" Only if they convey
>>the same meaning you may claim that I agreed with you. And, your inability to
>>distinguish between the meanings proves rather conclusively that you have no
>>understanding of what you're talking about. So, no smoke screens, just answer
>>what is the difference.
>
> Again, I made my point very clear -- from the beginning, I explained
>that Newton was wrong for exactly the reasons you later agreed with --
>as a matter of fact, I explained it over and over again, since the dullards
>I was speaking to failed to understand. You agreed with me two or three
>separate times -- I quoted a couple of them above.
No, each time I've stated specifically in what specific sense we may
consider Newton's theories to be inaccurate. I've also explained,
more times than I care to remember, why the statement "Newton was
wrong", as it stands, is either meaningless or plain false, in any
commonly used sense of the word "wrong".
There is a huge difference between saying that somebody is wrong on a
specific issue and saying that he is just wrong, period. For example,
just yesterday (or maybe it was two days ago) I've mentioned how
Einstein objected to quantun mechanics and that it turned out he was
wrong on this issue (that was a cue for you, by the way, but you
missed it). Now, is it justifiable, based on this, to say "Einstein
was wrong"? No. Is it justifiable to say "Einstein was wrong in his
assessment of quantum mechanics"? Yes. Is the difference clear to
you?
Now, you may claim that you don't have to accept my views on this
issue. That's legitimate. You may claim that you use the word
"wrong" in a different sense than I do. That's legitimate again. You
may claim that we argue over semantics and that there is no real
disagreement between our views. That's legitimate again (though I
would dispute it). But, when you say that I agreed with you without
me explicitly stating so, you commit a fraud. There are no ifs and
buts about it.
>(Have I pointed out that you're a little confused?)
Yes, lots of times. Whenever you did run out of arguments.
Mati Meron | "When you argue with a fool,
meron@cars.uchicago.edu | chances are he is doing just the same"
Subject: Re: what causes gravity? (remedial)
From: carlip@dirac.ucdavis.edu (Steve Carlip)
Date: 18 Nov 1996 18:15:13 GMT
Ken Fischer (kfischer@iglou.com) wrote:
: While gravity appears to be attractive, it isn't, unless
: again, you are discussing Newtonian gravitation.
: In General relativity, freefalling bodies are in inertial
: motion, and are _not_ accelerating, and so are definitely not
: attracted.
Well, this is a little misleading. We know intuitively what it
means to say that gravity is attractive---if I slip on the stairs,
the center of mass of the Earth and I move towards each other, not
away from each other---and there had better be a way of describing
this in general relativity.
There is, in fact. To look for attraction, it's not enough to
look at one object (which, as you say, is in inertial motion); you
have to look at at least two. There is an important theorem in
general relativity that says that as long as matter has positive
energy (in a suitable technical sense), if you start with a group of
objects that are initially at rest with respect to each other and
are interacting only gravitationally, the volume they take up will
always decrease in time. Gravity *is* attractive, in the sense that
it makes distances between objects decrease.
Steve Carlip
carlip@dirac.ucdavis.edu
Subject: Re: What is the Cause of Time Dilation?
From: devens@uoguelph.ca (David L Evens)
Date: 18 Nov 1996 18:38:23 GMT
Brian Jones (bjon@ix.netcom.com) wrote:
: devens@uoguelph.ca (David L Evens) wrote[in part]:
: >Brian D. Jones (bjon@ix.netcom.com) wrote:
: >: >: >>If a clock travels between two events, there's only one value for this
: >: >: >>particular clock, and it is an absolute reading, not a relative one.
: >: >: >>And the clock that has the greatest reading has taken the shortest
: >: >: >>absolute route between the two events, which is the absolute distance
: >: >: >>between them.
: >: >: >You seem to have shifted the meaning of absolute. You now have equated
: >: >: >absolute time with proper time. This is radically different than either
: >: >: >Newton's or Einstein's use of the term. I don't think that is what you
: >: >: >meant.
: >: >: A single clock traveling between events records a single time - this
: >: >: is clearly not relative, but absolute, or not observer dependent.
: >: >The problem with this demand is that the CLOCK becomes the observer.
: >: So who is Mr. Clock observing?
: >In this case, the clock is measuring the proper time for the world line
: >connecting the two events.
: The clock reading is an actual reading on an actual clock, and all
: inertial observers will agree as to its magnitude. This makes it an
: absolute quantity.
No, no other observer is guaranteed to agree that the clock in question
was observed to be running at the same rate as clocks in his own frame,
by which any other observer will measure time. Each observer will have
his or her own measurement of the interval, which is the interval in that
observer's frame.
: >: >: >>>: Obviously, for many events, there's not enough time for a clock to
: >: >: >>>: "span" them, even at lightspeed, so there would be no proper time for
: >: >: >>>: the events. This is the case above.
: >: >: >>
: >: >: >>>Yes, because we've switched from trig to hyperbolic trig.
: >: >: >>>We've switched from Pythagorus to Lorentz/Minkowski.
: >: >: >>>Thus, the interval is spacelike.
: >: >: >>
: >: >: >>>Oooooooo, scarey. Ooooooh. I dunno about you, kids,
: >: >: >>>but that sure convinces old Count Floyd, boy, I'll tell you. Oooooh.
: >: >: >>>--
: >: >: >>>Wayne Throop throopw@sheol.org http://sheol.org/throopw
: >: >: >>> throopw@cisco.com
: >: >: >>
: >: >: >>Sad and irrelevant attempt at being humorous.
: >: >: >>And what's really scarey is a clock that reads hyperbolic time!
: >: >: >>
: >: >: >Your use of absolute above would truly be hyperbolic time in the sense that
: >: >: >events at the same absolute time from the origin would occupy a hyperboloid,
: >: >: >rather than a plane. I will let you reconsider this one.
: >: >: But there's no proper time reading by a real clock.
: >: >No, the proper time is given by a clock carried by the observer or system
: >: >you want the proper time of.
: >: I meant that no real clock could travel between the events -- so there
: >: could be no real proper time recorded.
: >Now you are demanding that all clocks are constrained to be at rest in
: >your magical prefered frame?
: No, simply that the events were too far apart for a clock to span
: them, even at near c. In fact, some events cannot be spanned even by
: light.
If a clock cannot travel between two events, then neither event is in the
fiture light cone of the other, and they have no time-like interval
between them in ANY frame, so it makes no sense to try to talk about the
interval of a clock traveling between them.
--
---------------------------+--------------------------------------------------
Ring around the neutron, | "OK, so he's not terribly fearsome.
A pocket full of positrons,| But he certainly took us by surprise!"
A fission, a fusion, +--------------------------------------------------
We all fall down! | "Was anybody in the Maquis working for me?"
---------------------------+--------------------------------------------------
"I'd cut down ever Law in England to get at the Devil!"
"And what man could stand up in the wind that would blow once you'd cut
down all the laws?"
------------------------------------------------------------------------------
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e-mail will be posted as I see fit.
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Subject: Re: Bouncy Balls
From: jac@ibms46.scri.fsu.edu (Jim Carr)
Date: 18 Nov 1996 20:15:35 GMT
AJOHNSON@tech.lhs.davis.dist.k12.ut.us (ADAM JOHNSON) writes:
}
} Hello Me and my friend have this idea of stacking bouncy balls on top
} of each other and dropping them to launch a smaller ball on top into
} space is this possible
A very cool idea. You can calculate the mass ratio for a given height
of drop, or the height needed for a given mass ratio, and see what is
required. Of course, the simple calculation ignores air friction and
whether the collision will exceed the elastic limit of the materials,
but you can only find that out by doing some calculations and testing
them with experiments. Just be careful. (See comment at end.)
By the way, "space" is usually defined to be about 100 km up. You
cannot get into orbit this way (i.e. with a single impulse) since
the orbit will go through the launch point -- rockets don't just
go up, they follow a trajectory that puts them into an orbit.
sterner@sel.hep.upenn.edu (Kevin Sterner) writes:
>
>If we assume perfect elasticity, no friction, and no air resistance,
>the answer is no. You can't get any more energy out of the spring
>than you put into it, ...
No, but you can distribute it differently. I suspect Kevin has spent
too much time with those virtual HEP experiments where you view it all
through a computer. Get a basketball and a tennis ball and try it.
This demo is famous for being the most unpredictable one you can dare
try in lecture -- I know people who have taken the tennis ball in very
painful places. Doing it outdoors off of a building could break
windows or injure spectators.
--
James A. Carr | "The half of knowledge is knowing
http://www.scri.fsu.edu/~jac/ | where to find knowledge" - Anon.
Supercomputer Computations Res. Inst. | Motto over the entrance to Dodd
Florida State, Tallahassee FL 32306 | Hall, former library at FSCW.
Subject: Re: Teaching Science Myth
From: billb@eskimo.com (William Beaty)
Date: Mon, 18 Nov 1996 19:51:59 GMT
Elliot Weinberg (ellweinb@redshift.com) wrote:
: Conclusion, ice skating is possible predominately due to friction.
Butting in here: I saw a SCIENCE NEWS article on this debate within the
last year. The conclusion was that regelation is not the explanation.
The conditions in bulk ice are not the same as the conditions at the
surface, and this causes a layer of liquid water to be present even at
fairly low temperatures. Hence, ice comes pre-lubricated!
: These minor errors in textbooks or classrooms should not embarass or
: deter science teachers.
The damaging ones are those believed by the teachers and taught as fact in
textbooks. Once a science myth has spread to textbooks, it is very hard
to stop the "infection." I admit that this rarely happens at highschool
level and above, but at the K-6 level a major portion of the material is a
collection of myths. The K-6 textbook authors tend to inbreed by copying
each other rather than doing research. Like a game of "telephone" where
the transmitted phrase gets distorted by repeated transfer from person to
person, the sensible-yet-wrong explanations of science tend to be
reinforced by the habits of authors, and they tend to spread all through
the K-6 textbook arena.
I've made a small collection of these at:
http://www.eskimo.com/~billb/miscon/miscon.html
Also check out Frasiers "Bad Science" site, which contains even more
examples (my collection is mostly K-6 physical science). There's a link
on my site.
--
....................uuuu / oo \ uuuu........,.............................
William Beaty voice:206-781-3320 bbs:206-789-0775 cserv:71241,3623
EE/Programmer/Science exhibit designer http://www.eskimo.com/~billb/
Seattle, WA 98117 billb@eskimo.com SCIENCE HOBBYIST web page
Subject: Re: Sophistry 103 (was: I know that!)
From: "Hardy Hulley"
Date: 18 Nov 1996 18:31:25 GMT
brian artese wrote in article <328EB165.267B@nwu.edu>...
> Hardy Hulley wrote:
>
> > "[reading] cannot legitimately transgress the text towards something
> > other than it, toward a referent (a reality that is metaphysical,
> > historical, psychobiographical, etc.) or toward a signified outside the
> > text whose content could take place... There is nothing outside of the
> > text". (_Of Grammatology_, page 158)
> >
> > Now, go figure...
>
> I doubt you understand what this is saying. It simply refers to the fact
> that a text incites one to get at its meaning, or simply to talk about
> it, and that this is done by offering various paraphrases of what one has
> just read -- i.e., more articulation or more text. It doesn't mean that
> the Sears tower doesn't exist, as so many people like to believe so they
> can claim to 'know' that deconstruction is nonsense...
Oh no, my friend, it says much more than that. It says that the reader
cannot ever escape the text. He can never move from the text to a concrete
statement about the world outside of the text. My view is that this only
obtains for Derrida's own writing.
Cheers,
Hardy
Subject: Re: Fourier Transforms
From: breed@HARLIE.ee.cornell.edu (Bryan W. Reed)
Date: 18 Nov 1996 19:06:18 GMT
In article <56ot6b$r5n@mark.ucdavis.edu>,
I hate grading almost as much as taking in class exams wrote:
>
>Thanks for replying!
>
Beats working . . .
>: You neglected a solution to ik F(k) = 0, such that F was 0 everywhere except
>: at k=0. The general solution would be F(k) = F0 delta(k). Inverse Fourier,
>: and you get f(x) = an arbitrary constant, which is the general solution to
>: f'(x) = 0.
>
>
>So does that mean that
>
> f'(x) = 0 transforms into ik F(k) = F0 delta(k) ?
>
>I know that the inverse transform of a delta function yields a constant,
>so I was looking for a delta function. Are you saying that the zero of
>f'(x) = 0 transforms into a delta function?
>
>
No, it means that ik F(k) = 0, as you had, but that this equation implies
either F(k) = 0 or k = 0. So it says nothing about the value of F(0).
F(0) may be set arbitrarily, and when you transform back, you get the
arbitrary constant that is the solution to f'(x) = 0.
The relationship between F(0) and the constant value of f is a ratio of
some power of 2pi, depending on which version of the Fourier transform
you're using.
>: I'm curious--what background do you have that you understand the use of
>: frequency transforms to solve PDE's, but you've never seen Fourier used in
>: ODE's? That surprises me. My guess is that, like me, you learned ODE's
>: before you learned Fourier, and didn't recognize Fourier/Laplace techniques
>: at the time. But every time you assume a solution exp(sx) and rewrite the
>: ODE as an algebraic equation in s, you're using Laplace.
>
>I'm a little surprised that the use of fourier transforms for ODEs
>weren't mentioned. I've seen FT in a PDE class and a mathematical
>physics class, but it was always in the context of solving a PDE. All my
>ODE books have chapters on LT, but not FT. Actually, I'm a little
>embarassed now. I have only one book that goes into detail on FT
>(Mathematical Physics by Butkov), and again, it's only in the context of
>solving a PDE. Perhaps a recommendation of a good book on the subject
>would be in order? None of my ODE books breathe a word about the FT.
>
I don't know that I've ever seen a book that does a proper job of
explaining the use of Fourier in ODE's. At least, not as such.
If you solve the Schroedinger equation (time-independent) for a
1-d particle in an infinite potential well, you get a Fourier series.
Fourier series are applied to beam bending in some but not all texts
on the subject, sorry I don't remember any specific one that was of
value. Look for subjects like "Introductory elasticity", "strength
of materials," "beam bending," etc. I bet one of the many books by
Timoshenko covers it.
But then, if you understand the use of Fourier in PDE's, it doesn't
really matter that you've never studied them explicitly in the case
of a single independent variable. Anyway, Laplace tends to be more
useful in the case of ODE's.
Have fun,
breed
Subject: Re: The Character of a New Theory
From: coolhand@Glue.umd.edu (Kevin Anthony Scaldeferri)
Date: 18 Nov 1996 20:17:06 GMT
In article <56nu8s$7d8@pulp.ucs.ualberta.ca>,
Charles Cagle wrote:
>>
>>Classical physics is not in the trash can in spite of having been superseded
>>by QM. Classical physics is the correct practical theory to use for a
>>great many problems and will continue to be so.
>
>Trash can here meant rejected as not a perfect theory.
Should we then throw out all of our usable theories since all of them
are known to be imperfect? Should we talk only in terms of string
theory or quantum gravity (which _might_ be "perfect theories")
despite that neither one has ever made a testable or useful
prediction.
>Because a theory
>is useful for rough calculations (or even fairly accurate one's) doesn't
>mean we should be using it, unless, of course, we are satified only with
>estimates.
Again, were you under the illusion that there was any real physical
problem that we can solve exactly and completely?
>Moreover, there is a hidden danger in using a theoretical
>system which you know is less accurate than the facts. The danger lies in
>forgetting that it isn't true
I don't think any practicing physicist is likely to forget that
classical mechanics is just an approximation.
>(the Ptolemaic system retains some great
>accuracies but I doubt we would want to build upon it now seeing that
>something more accurate is available).
Actually, using Earth centered coordinates is vastly favorable for
the majority of what we do in space. Interplanetary probes probably
use heliocentric coordinates, although I wouldn't be surprised if
calculation within the Earth-Moon system are done with a geocentric
system, changing coordinates at a point when it become easier to use
heliocentric. Should we take into account the Sun's motion through
the Milky Way? The Milky Way motion within the Local Group? Still
larger formations?
If you think we should throw out "imperfect" theories, you need to
teach us how to build a bridge using only quantum mechanics first.
--
======================================================================
Kevin Scaldeferri University of Maryland
"The trouble is, each of them is plausible without being instictive"
Subject: Re: Hempfling's Cryonics bafflegab
From: tdp@ix.netcom.com(Tom Potter)
Date: 18 Nov 1996 22:16:49 GMT
In <328F5341.6858@earthlink.net> Immortal Being
writes:
>
>You disgust me, all religious freaks disgust me. I used to be Jewish,
in
>fact as a child I went to a Jewish school until I was 14, so I know
>everything about the religion, yet I belong to the true righteous
>movement. THE ATHEIST MOVEMENT! Our world is too advanced to still
>believe in religion. In 100 years we should be free of the chains of
the
>religion drug. I am NOT A COMMUNIST!
As a non-religious person, it seems to me that
it would be extremely difficult and time consuming
to raise good atheist kids as they would tend to
have casual attitudes toward lying, stealing,
having casual sex, keeping their words, etc.
Now, I raised three good, moral, athiest kids,
but I must state that I had to deal with all
moral issues on a one to one basis. It would
be much easier to tell them that some God
will deal with them, IF they do not conform to
some laundry list of rules.
Frankly, I have come to respect the concept
of religion as I come to understand more
about the world around me. I suggest that
the better societies would evolve the
laundry list of rules over some time,
and that this would be better than for
the people in a society to be whiplashed
with constantly changing mores, promoted
by government, industry and media.
Tom Potter http://pobox.com/~tdp
