HDTenEightyP/NetNews huggingface dataset:
From: ejlund@coos.dartmouth.edu (Eric J. Lund)
Newsgroups: sci.physics
Subject: Re: Inelastic versus Elastic
Date: 22 Nov 92 17:45:59 GMT
Organization: Dartmouth College, Hanover, NH

BBLAIS@eagle.wesleyan.edu (BRIAN S. BLAIS) writes:

>A friend of mine wrote me:
>--
>Suppose that you have a bullet running into a block. It does so in a perfectly
>inelastic manner. That is, the bullet stays in the block after the collision
>imparting its momentum into the combination of itself and the block. However,
>some of the energy of the motion is lost in the form of heat, so kinetic
>energy is not conserved.

>Why? I am looking for an intuitive explanation of the conservation of moment
>that allows one to see clearly and distinctly that, even though some of the
>quantity of motion is converted into heat, the quantity of motion as expressed
>by _mv_ remains the same.
>--

>	I was trying to think of some reply to this, and thought that people
>one the Net might like thinking about it.  I would like to know if anyone has
>any good way of looking at this problem.

>			Brian Blais

The atoms of the bullet and the block have random motions. The greater the
random motion, the "hotter" the substance. When the bullet hits the block,
the atoms of both are kicked violently, hence more random motion. There's
also some potential energy in the stretching of interatomic bonds. Some of
the kinetic energy of the bullet also goes into moving air molecules, so
you hear a sound when the bullet hits. I may be overlooking something, but
that's the general idea.

Eric Lund
From: sichase@csa3.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: Re: energy, mass, and all that
Date: 20 Nov 1992 07:12 PST
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
Distribution: world
NNTP-Posting-Host: 128.3.254.198
News-Software: VAX/VMS VNEWS 1.41    

In article <1992Nov19.195724.97834@watson.ibm.com>, platt@watson.ibm.com (Daniel E. Platt) writes...

>When 'mass' is destroyed, and 'energy' is created, actually, what's happening
>is some kinds of particles are anihilated, and some are created.  For instance,
>in electron-positron anihilation, 2 photons are created; there's Feynmann
>diagrams for the processes, and cross-sections may be computed, to yield
>spectra, etc.  There's no energy without some particular kind of particle
>to carry the energy.  However, there's different kinds of particles that
>CAN carry the energy, and the total mass of the particles after the
>reaction may be different than the mass before the reaction; the total
>mass-energy (E^2 = p^2 + m^2) must be conserved (reflected in a delta-function
>in the S-matrix).  Even here, saying that the mass was 'converted' to
>energy is a misnomer; photons were created that carry the energy in a 
>way characteristic of the photon dispersion relationship: E=pc (omega = c|k|).

What about after the photon is absorbed by some material, increasing
the kinetic energy of the material?  Are we going to say that there is 
no such thing as heat energy, only mass increase of the material?  I
suppose you are free to do so, but I find this to be (a) a very big 
stretch, and (b) a useless formulation for solving most problems.  

Martin Watts wants to say that mass and energy are non interconvertible.
That is, when Martin came into the world, there was so much mass and 
so much energy.  From that point in time, he will say that all the
mass that became energy is really still mass, and all the energy that
became mass is really still energy.  Isn't this unphysical?  You have
to argue so hard to demonstrate that all mass continues to be mass that
you practically have to eliminate the possibility that energy exists in
the Universe (As you did above.)  Similarly, you have to argue so hard
that energy never becomes mass that you practically have to eliminate
the possibility that mass exists.  

-Scott
--------------------
Scott I. Chase			"It is not a simple life to be a single cell,
SICHASE@CSA2.LBL.GOV		 although I have no right to say so, having
				 been a single cell so long ago myself that I 
				 have no memory at all of that stage of my 
				 life." - Lewis Thomas
From: u108502@beta.lanl.gov (Andrew Poutiatine)
Newsgroups: sci.physics
Subject: Re: pressure questions
Date: 17 Nov 92 15:30:23 GMT
Article-I.D.: newshost.1992Nov17.153023.11618
Organization: Los Alamos National Laboratory

In article <9729@blue.cis.pitt.edu.UUCP> gswst@cislabs.pitt.edu (Gary S. Wachs) writes:
>
>
>This past week I took SCUBA lessons (Openwater, PDIC) and talked about 
>the effects of pressure quite a bit.    As we descend into the water,
>the ambient pressure increases, compressing us.  The degree to which
>something is compressed depends on whether is is a solid, liquid or gas.
>
>Therefore, if we took an extremely thick-walled metallic box with a 
>hollow center filled with a cubic foot of air at sea-level pressure  of
>1 atmosphere, I believe that the metal would be so resistent to 
>compression that the hollow air pocket inside would not see a change in
>pressure.  Yes it is changing altitude, but it is isolated from the 
>crushing forces of pressure outside the box, it won't be effected. 
>
>Now then, am I way off or is that correct?
>
>Thanks in advance...
>
>
>
>
>


You are about 99% correct.  Since we know it is possible to build vacuum
chambers, it is possible to construct a "box" to withstand a greater ambient
pressure.  So yes, you can easily construct a "box" to submerge below the
ocean surface and maintain a relatively constant internal pressure (or a 
constant internal pressure if you can vent some of the gas).

The only very small problem is that all materials compress, or more generally
strain, in the presence of a stress.  There is no perfectly rigid material.
Thus even the thickest box will deform under the influence of even the smallest
stress.  To this extent, the inside gas *will* feel the outside pressure effects, but admittedly to only a miniscule degree.

Consider deep water subersibles and submarines.  Typically (but not always) the
crew inside is kept at near atmospheric pressures so that when surfacing from
depth decompression is not a problem, and the crew does not get "bent."

-AIP
From: bweiner@ruhets.rutgers.edu (Benjamin Weiner)
Newsgroups: sci.physics
Subject: Re: Ferromagnetism and the Clash of Cultures
Date: 17 Nov 92 23:40:49 GMT
Organization: Rutgers Univ., New Brunswick, N.J.

jbaez@riesz.mit.edu (John C. Baez) writes:
>  ...  the frustrations of trying to communicate across culture
>gaps.  You are using terminology I think I understand but in ways that
>are completely mysterious to me.  E.g., "a gap opens in the top of the
>spectrum."  I know what a spectrum is and what a gap in one is, but
>thinking of the spectrum as a dynamical variable subject to change
>("opens") is foreign to me (perhaps the implicit reference to time in
>"opens" is somewhat metaphorical?).  

Yeah, the meaning is "in the normal case X happens, but when we include
this effect, a gap opens in the top of the spectrum." 

>Also, I understand the concept of exchange energy but don't get how it
>is less when spins are lined up for ferromagnets.

It's complicated.  It has something to do with the fact that the
electrostatic repulsion favors the states where the electrons are
more separated, and Pauli exclusion means that parallel spins are more
separated.  There are holes in that toy idea; clearly it's a subtle and
complicated effect, since most materials are not ferromagnetic.

>Sigh.  I'm sure I am equally incomprehensible to most experimentalists.

Hey, I'm still not sure what a symmetry group should have to do
with the number of fermions, or anything like that, or, sorry John,
what a holonomy is.

>Or is that physicists who specialize in "fundamental" physics don't
>always learn enough about solid state to talk about it in a
>rough-and-ready sort of way?  Maybe this has something to do with why
>there's not much talk about solid state on sci.physics?

That could have something to do with it; another speculation might be
that it's not just solid-state; in many fields there are both
fairly abstruse mathematics and fairly involved experimental techniques,
and it's harder to explain how and why the experiments are so involved.
And people don't want to hear about experimental techniques anyway.

One factor for sci.physics is that much of this discussion is driven by 
people trying to explain to novices, and novices tend to ask about the
gee-whiz stuff.  Even outside the realm of crackpots, people tend to
want to hear about the flashy, big, often highly theoretical things.
And physics has a long-standing tradition of "theoretical macho,"
where he who is most mathematical wins.  The converse is that in such
a forum as this, the professional physicists will ask questions
which are out of their realms of expertise, and often that means moving
up the theory scale, so to speak.

- Ben
From: drucker@csa1.lbl.gov (BOB DRUCKER, BERKELEY/LBL)
Newsgroups: sci.physics
Subject: Re: Flying fast enough and becoming a black hole
Date: 20 Nov 1992 15:32 PST
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
Distribution: usa
NNTP-Posting-Host: 128.3.254.196
News-Software: VAX/VMS VNEWS 1.41    

In article <SRCTRAN.92Nov19111841@world.std.com>, srctran@world.std.com (Gregory Aharonian) writes...
>   I just finished reading a science fiction (actually with an Islamic
>setting, a rarity in the field), which had as one of the main points of
>the story that if you built a spaceship and continually accelerated,
>eventually you relativistic mass, for the size of the spaceship, would
>be large enough to cause collapse into a blackhole.

     Thinking in terms of "relativistic mass" can sometimes lead you 
astray; this is a good example of that.

     The energy of a moving mass m is  E = mgc^2, where g is gamma = 
sqrt(1/(1-(v/c)^2)), and m is the rest mass.  This is often interpreted
as E = Mc^2, where M is the "relativistic mass" M = mg.  However, the 
mass of an object is best considered to be it's rest mass m. No matter
what the speed of an object, in it's own rest frame it has mass m
(NOT mg).

     As the other response to this thread points out, if the object is 
not a black hole in it's rest frame, then it isn't one in some other 
frame.

Bob Drucker
Newsgroups: sci.physics
From: frisinv@alleg.edu
Subject: Showing change in flux
Organization: Allegheny College
Date: Fri, 20 Nov 1992 03:02:53 GMT

   I am looking for a visually obvious way of showing a change in flux  
(with respect time or position) that doesn't rely on the audience knowing  
that much about induction. I need it for a non-rigorous lecture on  
Maxwell's equations and thought that a demonstration would be a good way  
of dealing with flux before I dive into Faraday's law (that's why I can't  
expect them to know induction well). I realize that most of the people  
listening will be at least familiar with the concept, but I don't want to  
leave any holes. Please email a suggestion or two.

Vincent Frisina: frisinv@alleg.edu
--
Newsgroups: sci.physics
From: snil@daimi.aau.dk (Sven Nielsen)
Subject: How can you measure the following ?
Summary: A problem !
Keywords: stopwatch
Organization: DAIMI: Computer Science Department, Aarhus University, Denmark
Date: Thu, 19 Nov 92 11:55:52 GMT

In how many ways can you measure the height of a tall building using only
these three tools : Stopwatch, barometer and tape measure.
Now use your imagination. I'll give a few examples :

1. Throw the barometer out from the top of the building and use the stopwatch
to measure the time it takes before the barometer hits the ground. The height
h = g/2 * t^2 ............

2. Make a pendulum of the barometer and the tape measure. Lower the barometer
until it almost touches the ground then let it swing and measure the period 
using the stopwatch.  h = g * T^2 /(4*pi)^2   (I think ...)

3. While doing 2. just read out the value on the tape measure.

Your turn now ......   Sven (snil@daimi.aau.dk)

Newsgroups: sci.physics
From: 92bbb@williams.edu (Bradford Behr)
Subject: Re: How can you measure the following ?
Keywords: stopwatch
Organization: Williams College, Williamstown, MA
Date: Thu, 19 Nov 1992 15:03:28 GMT

In article <1992Nov19.115552.16917@daimi.aau.dk> snil@daimi.aau.dk (Sven Nielsen) writes:
>In how many ways can you measure the height of a tall building using only
>these three tools : Stopwatch, barometer and tape measure.

Find a pawn shop. Sell the stopwatch, barometer, and tape measure.
Hire a graduate student or unemployed ex-Soviet physicist to do the
measurement.

:)

Brad
Newsgroups: sci.physics,sci.logic
From: gsmith@lauren.iwr.uni-heidelberg.de (Gene W. Smith)
Subject: Re: Lowneheim-Skolem theorem
Followup-To: sci.logic
Organization: IWR, University of Heidelberg, Germany
Date: Fri, 20 Nov 92 14:01:59 GMT

In article <361@mtnmath.UUCP> paul@mtnmath.UUCP (Paul Budnik) writes:

>This would be a valid argument if uncountable had an absolute definition.
>I think uncountable is only meaningful relative to some formal system. 

"Uncountable" means no one-to-one relation with the integers
can be given.  This does not refer to a formal system.

>There are plenty of examples of sets uncountable in one system that
>are countable in stronger systems.

If they are countable in the stronger system, that means that
a one-one map can be found in it, which means that these sets
are countable.

>The question of whether uncountable has an absolute definition is a
>philisophical one that I expect we have different opinions on.

I say "uncountable" means what mathematicians mean by it.  This is
more a linguistic question than a philosophical one.






-- 
     Gene Ward Smith/Brahms Gang/IWR/Ruprecht-Karls University 
               gsmith@kalliope.iwr.uni-heidelberg.de
Newsgroups: sci.physics
From: kkretsch@unix1.tcd.ie (kevin patrick kretsch)
Subject: Re: UFO EVIDENCE VS. Carl Sagan
Organization: Trinity College, Dublin
Date: Thu, 19 Nov 1992 12:29:21 GMT

O.K., it seems that alot of good discussion has come of this,
the main question semms to be on the lines of:
    "How are UFOs powered between planets if they require
the magnetic field of a planet for propulsion?"

Good question, and like many people I don't know, and who
does? If they did and they told everyone about it we wouldn't
be wondering now. 
      As Leigh Palmer pointed out, UFOs dont need propulsion
in open space and that seems pretty logical to me, although
I do wonder if the combined solar wind from many stars would
have any effect on the 'spaceship'.      
      Let us also that IF little green men are travelling
through space across vast distances in (presumably) short
times, they obviously are much more advanced than us
and thus would have answered correctly all our questions 
and built themselves a craft to take them to places not 
even heard of in National Geographic magazine!
      Assuming that space travellers are so advanced not
just technologically but emotionally could answer other
questions also. Could it be that the human race is to
primitive to be able to use this technology without
destroying ourselves (as we have nearly done with nuclear
power ?). Perhaps our alien visitors decided after observing
us at close range that this being the case this technology
should be witheld from us?
      Maybe this is why aliens never landed live on the Johnny 
Carson show or turned up at EXPO '92!!
      In answer to John Snyder's question, "Why hasn't one
(a UFO) crashed where the media could get to it first?"
I believe the answer to be this,
      This probably has happened, on a number of occaisions
but the military, predictably with decent tracking equipment,
got ther in time to prevent any publication of these landings
in the 'interests of national security' or to prevent public
punic and general mayhem. As a result, any photographs of such
landings are rare enough tobe written off as faked.

Sorry 'bout the lenght.

Kev.


     C
C
primitive to be able to use te
From: ucap22w@ucl.ac.uk (Martin S T Watts)
Newsgroups: sci.physics
Subject: Re: TIME HAS INERTIA
Date: 17 Nov 92 14:40:29 GMT
Organization: Bloomsbury Computing Consortium

bweiner@ruhets.rutgers.edu (Benjamin Weiner) writes:

>sichase@csa1.lbl.gov (SCOTT I CHASE) writes:
>:>>> ucap22w@ucl.ac.uk (Martin S T Watts) writes...
>:
>:>>(And if you think that, say, positron-electron annihilation is an example of
>:>>the destruction of mass, then think again.)
>:
>:>Sure.  What would *you* call it?  Where do *you* think the mass goes?
>:
>:>>It wouldn't surprise me if American Universities were turfing out copies of
>:>>J. Phys. A! I only included the reference in case people doubted the
>:>>authenticity of my claim - I hadn't thought people would go to the trouble
>:>>of looking it up. 

>Etc.  Scott, don't you imagine this whole tempest-in-a-teapot is the old
>confusion over "relativistic mass" versus "rest mass"?  Bondi probably
>said that mass is conserved, meaning relativistic mass, which is just a
>statement of conservation of energy less a factor of c squared.  Rest
>mass isn't conserved.

Exactly. Congratulations!

I don't believe that Scott Chase realises this, however, if he thinks that
mass is lost in particle-antiparticle annihilation.

>To the original poster, it's all very easy to blame your problems on
>the nasty, horrible, mediocre American university system.  Especially when
>you're writing from Britain, where the universities are all gleaming
>castles-on-a-hill, which are so well funded that they actually lure
>American faculty away!!!  (Sorry to be mean, but motes in the eye and
>all that)

Hey, hold on a minute. MY problems? It isn't me who's got problems. I just
had the misfortune to reference an article which Scott Chase had trouble 
finding. I hardly think that necessitates your having a go at the British
University system. It's not *their* fault that they have difficulty in 
getting funding.

Martin Watts.
From: cam@castle.ed.ac.uk (Chris Malcolm)
Newsgroups: sci.physics
Subject: Re: Slip-sliding away (was Re: What would you ride...)
Date: 23 Nov 92 18:41:04 GMT
Organization: Edinburgh University

Here is a diagram of a bike moving from left lean to right lean.
Because the tire is not knife edged but round, in doing this it rolls
from left to right. So, as can be seen, the centre of bike rotation
with respect to the road is underneath the road. It's so easy to
forget these little details isn't it?

                

                   \                /
                    \              /
                     \  .      .  /
                   .     .    .     .
                    .    .    .    .
                      . .      . . 
                  ---------------------------- road

                          \ /
                           .  -- centre of rotation



-- 
Chris Malcolm    cam@uk.ac.ed.aifh          +44 (0)31 650 3085
Department of Artificial Intelligence,    Edinburgh University
5 Forrest Hill, Edinburgh, EH1 2QL, UK                DoD #205
Newsgroups: sci.physics
From: sichase@csa2.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: Re: Higgs Spotted?
Date: 16 Nov 1992 10:21 PST
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
Distribution: world
NNTP-Posting-Host: 128.3.254.197
News-Software: VAX/VMS VNEWS 1.41    

In article <MATT.92Nov14111225@physics.berkeley.edu>, matt@physics.berkeley.edu writes...
>In article <1992Nov14.185501.26643@cs.yale.edu> jhh@waldzell.physics.yale.edu (Jim Horne) writes:
> 
>> I heard this third hand from someone who talked to someone who heard
>> the talk at Fermilab last week where this was discussed. There are
>> six events of e^+ + e^- -> Z^0 -> e^+ + e^- + \gamma + \gamma, which
>> seem to give a mass of 60 GeV (the e's in the final state can also
>> be \mu's).  This shouldn't be the higgs because the decay mode is
>> wrong. It's not clear what it could be, but someone mumbled
>> "technipion". In any case, the person who heard the talk thought it
>> was just background, and not a real signal.  Given past history, I
>> would bet that these events are indeed just background, and don't
>> represent a new particle.
> 
>There's another reason why it can't be the Higgs, and probably isn't a
>particle at all: contrary to appearances, it isn't a peak!  That is:

There is more call for skepticism, perhaps, than most people would 
think.  We have been through this so many times that I have almost zero
expectation that this will amount to anything.  Six months ago it was
an anomalous rate of e+ + e- -> Z0 -> four leptons that had people excited.
Today it's two leptons and two photons.  Tommorrow it will be three photons
and a grapefruit.  In the end, in my experience, 9 out of 10 (if not more!) 
such claims quietly fade away.  

What we have here is some graduate student who sifted through tens of 
gigabytes of data, 100's of thousands of (presumed) Z0 decays to find
7 events which are thought to belong to a certain class.  There are 
dozens of reasons why these events might not be real - and I guarantee
that when the results are *first* announced, most of these possibilities
have not been scrutinized enough.  

-Scott
--------------------
Scott I. Chase			"It is not a simple life to be a single cell,
SICHASE@CSA2.LBL.GOV		 although I have no right to say so, having
				 been a single cell so long ago myself that I 
				 have no memory at all of that stage of my 
				 life." - Lewis Thomas
Newsgroups: sci.physics
From: weemba@sagi.wistar.upenn.edu (Matthew P Wiener)
Newsgroups: sci.physics
Subject: Re: energy, mass, and all that
Date: 19 Nov 92 19:32:54 GMT
Reply-To: weemba@sagi.wistar.upenn.edu (Matthew P Wiener)
Organization: The Wistar Institute of Anatomy and Biology
In-reply-to: sichase@csa1.lbl.gov (SCOTT I CHASE)

In article <19NOV199211063691@csa1.lbl.gov>, sichase@csa1 (SCOTT I CHASE) writes:
>If energy and matter are not interconvertible, where does all the energy
>of an atomic bomb blast come from?  

Simple.  The energy that used to be binding is now blast, light, heat.
While it was binding, the energy was localized enough that we could
weigh it directly, and so the bomb weighed E-bind/c^2 more than it
would have otherwise.
-- 
-Matthew P Wiener (weemba@sagi.wistar.upenn.edu)
From: cburian@ux4.cso.uiuc.edu (Christopher J Burian)
Subject: Re: _Voltage_ ratings of fuses
Organization: University of Illinois at Urbana
Date: Sun, 22 Nov 1992 01:22:47 GMT

palmer@sfu.ca (Leigh Palmer) writes:

>In article <1egpleINNie8@crcnis1.unl.edu> cbettis@unlinfo.unl.edu (clifford
>bettis) writes:
>>
>>The other day the fuse blew in our microwave oven and in the process 
>>of replacing it, I noticed it had a voltage as well as a current 
>>stamped on it. I'd been aware of this before but never really thought 
>>about it. Why is there a voltage rating for a fuse; is it a matter of 
>>how much resistance the fuse has, or possibly some sort of breakdown 
>>by arcing limitation? If it is a matter of resistance, why not always 
>>use the fuse with a lower voltage rating? 

>After the fuse blows there may be a voltage drop across it. That's what one has
>to worry about.

>I have replaced the fuse in my microwave oven twice. To do so I have to take
>the whole case off the damn thing - they were too cheap to put on a shielded,
>socketed fuse. Do you have the same problem? I note that there is an access
>door to the oven light bulbs. 

>I'm sure lots of perfectly serviceable microwave ovens get discarded when thay
>blow fuses because of this "feature". It is probably due to some unreasonable
>radiation requirement for these beasts.

>Leigh

The voltage rating of a fuse is an arcing limitation.  As one examines
fuses of higher ratings they are longer, and filled with sand that melts
to provide an insulating barrier.

Microwave oven fuses are *not* easily replaced for safety reasons.  The
manufacturers want qualified service personnel to replace the fuses only
after determining the cause of the failure.  Manufacturers are also very 
concerned about the integrity of the shielding.  The fuse often blows
because the door safety switch has failed.  It more often blows due to
age, but they don't want to take chances with lawsuits.

	Chris Burian---

Newsgroups: sci.physics