[NatureNS] Correction; Fw: Velocity of light

From: David & Alison Webster <dwebster@glinx.com>
To: naturens@chebucto.ns.ca
References: <5A9443B08B714115A5AAA3DA875A05EB@D58WQPH1>
Date: Sat, 22 Sep 2012 20:18:04 -0300
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 that has nagged me for decades. Perhaps someone can clarify.=0A&gt;&gt;&gt;&gt;=0A&
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Hi Patrick & All,                    Sept 22, 2012
    Thanks for the detailed explanation. I have read this several times =
and will give it further study. We agree that mass, by definition, will =
be independent of the setting and that weight will vary depending upon =
gravity.=20

    But even the determinations of mass on an equal-beam balance will be =
influenced by ambient gas pressure unless the reference mass and the =
unknown mass have equal volume. And a beam balance will register noise =
(I expect) at zero gravity.

    Going to the moon to test this is expensive and, in any case, one =
would need permission of the owners. It is more convenient to consult a =
Quantitative Chemistry text. If  the unknown object is not as dense as =
the reference, then 'mass' of the unknown will appear to increase when =
gas is removed from the balance. And my Quantitative Chem. text states =
that "Thus the mass of the object in vacuum is greater than that =
measured in air..."

    But, on the other hand, if the unknown is more dense than the =
reference then 'mass' of the unknown will appear to have decreased when =
gas is removed. Wow we have just created and destroyed matter with a =
vacuum pump.=20


    It gets much worse if you use a weighing system in which no =
reference 'mass' is concurrently used, e.g. a spring scale calibrated on =
earth using a series of references 'masses'. The mass will appear to be =
much less on the moon and become zero at zero gravity.

    Therefore, even an equal-beam balance does not really measure mass. =
It is responding to F which is equal to mg, the two arms being in =
balance when the reference F, by nature of the equipment design, applies =
an upward force F that equals the downward F of the unknown when the two =
are in balance.

    I suspect that the different conventions over time reflect different =
contexts. If you dealt with objects at rest (e.g. preparation of =
reagents) then weight would be standard usage (sometimes called mass to =
appear learned). If you dealt with objects in motion then mass would be =
standard.=20

    Units are only as good as they are useful. I notice that spring =
scales are now calibrated in Newtons. How would one check that =
calibration ? With a box of standard Newton Forces ? =20

    It will just take a while and probably a fresh set of participants =
to make the adjustment.=20

    I still buy apples by the pound but to prepare for the changeover; a =
Newton of apples will be one apple. Right ?

Yt, Dave Webster, Kentville

    =20
  ----- Original Message -----=20
  From: Patrick Kelly=20
  To: naturens@chebucto.ns.ca=20
  Sent: Saturday, September 22, 2012 11:28 AM
  Subject: Re: [NatureNS] Correction; Fw: Velocity of light


  I'm not sure I see the confusion arises over the kg being a unit of =
mass. I just covered this in my last astronomy class and why people use =
the words mass and weight interchangeably when they are two totally =
different things. Mass is a measure of how much matter an object =
contains. You measure mass with a scale. A 1 kg bag of sugar has the =
same mass here as well as on the Moon, as on a scale you would still =
need a 1kg mass to balance it.


  Weight is a force, not a measure of mass. The problem is not helped =
when people still use the English unit of "pound" for both weight and =
mass. The English system unit of mass is the slug, not the pound. Your =
weight is the force of gravity acting on your mass and depends on your =
mass, the mass of the Earth and the radius of the Earth. if you are =
standing on the Moon (different mass and radius) you will "weigh" less =
because the gravitational force is less. If you stood on a doctor's =
scale on the Moon you would find that your mass is the same as it is on =
Earth.


  In the metric system, the unit of force is the Newton (the symbol is =
N). 1 N is the force that is required to accelerate a 1 kg mass at the =
rate of 1 m/s/s. (i.e. Force =3D mass X acceleration).=20


  At the surface of the Earth, the gravitational force =3D G x m x M / =
(r x r), where G is the gravitational constant, m is the mass of a small =
object (like a person), M is the mass of the Earth and r is the radius =
of the Earth.


  If you drop that small object, this force will also produce an =
acceleration (because Force =3D mass X acceleration). So F =3D m x a. =
Since the force comes from gravity:


  m x a =3D G x m x M / (r x r)


  Note that since the small object is on both sides of the equation, you =
can cancel it, and thus you get:


  a =3D G x M / (r x r)


  This acceleration gets a special symbol, g, and has a value of 9.8 =
m/s/s (which you can round of to 10 m/s/s). This is the rate at which =
all objects at the surface will fall (in a vacuum). If you go to the =
Moon, since M and r are different the surface gravity there is much =
lower, 1.7 m/s/s of about 1/5 that of the Earth.


  You can also use the surface gravity as a quick way to calculate your =
"weight" by multiplying your mass (in kg) by g. A 1 kg mass has a =
"weight" of 9.8 N and a person such as myself with a mass of about 100 =
kg would have a weight of 980 N. Thus a proper metric scale would NOT be =
graduated in kg, but in Newtons. I expect there are two reasons they =
don't. One is that most people would freak if their "weight" appeared to =
be 10 times what they thought it was, and secondly, since they assume =
you are using the scale at the Earth's surface, they have "converted" =
the force back into "mass". Just don't take it to the Moon and expect it =
to work properly!


  Pat


  PS: For those who are curious, a mass of 1 slug has a weight at the =
Earth's surface of 32 pounds.








  The kg a unit oef mass=20

  On Sep 22, 2012, at 9:58 AM, David & Alison Webster wrote:


    Hi Fred & All,                    Sept 22, 2012
      Explanations of weight/mass usually resemble inconsistent =
confessions obtained by torture but I guess that is ok now.

      It seems logical to me that weight should be treated as a special =
case of F=3Dma where a in this case is g and F is measured by exerting =
an equal and opposite force upward to keep the mass from falling.

      One could then determine the magnitude of mass as F/g and then =
proceed to work out units of momentum, inertia etc from there.

      But unfortunately kg has been defined (or perhaps redefined) as a =
unit of mass which leads to everything being a hopeless muddle.

      I would try to reform the system of units dealing with weight, =
mass and distance but I am tied up this afternoon.

    Yt, Dave Webster, Kentville
    ----- Original Message ----- From: "Fred Schueler" <bckcdb@istar.ca>
    To: <naturens@chebucto.ns.ca>
    Sent: Friday, September 21, 2012 9:19 PM
    Subject: Re: [NatureNS] Correction; Fw: Velocity of light



      Quoting David & Alison Webster <dwebster@glinx.com>:



        I just dug out my 1st yr Physics (Weber, White & Manning, 1952) =
and  they consistently refer to 'speed of light' as opposed to 'velocity =
 of light'. Four other sources (1941, 1948, ~1965 &1962) have velocity.



      * indeed, it would be ineffective to purge society, or even  =
literature, of all who misuse speed/velocity or weight/mass. Or, to  =
bring it closer to natural history, all who refer to nonhemipterans as  =
"bugs."



      fred.

      =
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D



        ----- Original Message ----- From: "David & Alison Webster" =
<dwebster@glinx.com>

        To: <NatureNS@chebucto.ns.ca>

        Sent: Friday, September 21, 2012 7:44 PM

        Subject: Velocity of light





          Dear All,                        Sept 21, 2012

           The recent discussion about transmission of electricity, =
reading  of HEAT and reading some of Energy... brings to the forefront a =
 question that has nagged me for decades. Perhaps someone can clarify.



           In the typical elementary physics text we are told that =
velocity  is a vector quantity, and to quote one text "velocity... may =
be  defined as the rate of change of position in a given direction".  =
But "In cases where the direction of motion does not require to be  =
considered , the term speed is employed to express the rate of  =
travelling."



           Based on the above I would think that the rate of movement of =
 light should be called speed, i.e. speed of light but I think it is  =
always called velocity.

          For example, if light from the sun is reflected from two 45o  =
mirrors then a beam of light could be directed from the earth back  to =
the sun and, the velocity would then be minus 3 x 10^10 cm/sec.  Or if =
variously scattered or reflected then the velocity, relative  to the =
initial sun to earth direction, would always be less than 3  X 10^10 and =
after several reflections might be zero.



           Is there some good reason why the speed of light is termed  =
velocity of light ? Or is it called velocity because the textbook  =
authors forget what they said in chapter one by the time they write  =
chaper eleven ? (And they all copy from each other)

          Yt, Dave Webster, Kentville











      ------------------------------------------------------------

              Frederick W. Schueler & Aleta Karstad

      Bishops Mills Natural History Centre - =
http://pinicola.ca/bmnhc.htm

      Mudpuppy Night in Oxford Mills - http://pinicola.ca/mudpup1.htm

      Daily Paintings - http://karstaddailypaintings.blogspot.com/

              South Nation Basin Art & Science Book

              http://pinicola.ca/books/SNR_book.htm

         RR#2 Bishops Mills, Ontario, Canada K0G 1T0

        presently in Cochrane  - 49.06274N 81.02415W -

                on the great Ontario Claybelt

        (613)299-3107 <bckcdb at istar.ca> http://pinicola.ca/

      ------------------------------------------------------------







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http-equiv=3DContent-Type>
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<STYLE></STYLE>
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style=3D"WORD-WRAP: break-word; -webkit-nbsp-mode: space; =
-webkit-line-break: after-white-space"=20
bgColor=3D#ffffff>
<DIV><FONT size=3D2>Hi Patrick &amp; All,&nbsp;&nbsp;&nbsp; =
&nbsp;&nbsp;&nbsp;=20
&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp; Sept 22,=20
2012</FONT></DIV>
<DIV><FONT size=3D2>&nbsp;&nbsp;&nbsp; Thanks for the detailed =
explanation. I have=20
read this several times and will give it further study. We agree that =
mass, by=20
definition, will be independent of the setting and that weight will vary =

depending upon gravity. </FONT></DIV>
<DIV><FONT size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2>&nbsp;&nbsp;&nbsp;&nbsp;But even the determinations =
of mass on=20
an equal-beam balance will be influenced by ambient gas pressure unless =
the=20
reference mass and the unknown mass have equal volume. And a beam =
balance will=20
register noise (I expect) at zero gravity.</FONT></DIV>
<DIV><FONT size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2>&nbsp;&nbsp;&nbsp; Going to the moon to test this is =
expensive=20
and, in any case,&nbsp;one would need permission of the owners. It is =
more=20
convenient to consult&nbsp;a Quantitative Chemistry text. If&nbsp; the =
unknown=20
object is not as dense as the reference, then 'mass' of the unknown will =
appear=20
to increase when gas is removed from the balance. And my Quantitative =
Chem. text=20
states that "Thus the mass of the object in vacuum is greater than that =
measured=20
in air..."</FONT></DIV>
<DIV><FONT size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2>&nbsp;&nbsp;&nbsp; But, on the other hand, if the =
unknown is=20
more dense than the reference then 'mass' of the unknown will appear to =
have=20
decreased when gas is removed. Wow we have just created and destroyed =
matter=20
with a vacuum pump.&nbsp;</FONT></DIV>
<DIV><FONT size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2></FONT><FONT size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2>&nbsp;&nbsp;&nbsp; It gets much worse if you use a =
weighing=20
system in which no reference 'mass' is concurrently&nbsp;used, e.g. a =
spring=20
scale calibrated on earth using a series of references 'masses'. The =
mass will=20
appear to be much less on the moon and become zero at zero =
gravity.</FONT></DIV>
<DIV><FONT size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2>&nbsp;&nbsp;&nbsp; Therefore, even an equal-beam =
balance does=20
not really measure mass. It is responding to F which is equal to mg, the =
two=20
arms being in balance when the reference F, by nature of the equipment =
design,=20
applies an upward force F that equals the downward F of the unknown when =
the two=20
are in balance.</FONT></DIV>
<DIV><FONT size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2>&nbsp;&nbsp;&nbsp; I suspect that the different =
conventions=20
over time reflect different contexts. If you dealt with objects at rest =
(e.g.=20
preparation of reagents) then&nbsp;weight would be standard usage =
(sometimes=20
called mass to appear learned). If you dealt with objects in motion then =
mass=20
would be standard. </FONT></DIV>
<DIV><FONT size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2>&nbsp;&nbsp;&nbsp; Units are only as good as they =
are useful.=20
I notice that spring scales are now calibrated in Newtons. How would one =
check=20
that calibration ? With a box of standard Newton Forces&nbsp;?=20
&nbsp;</FONT></DIV>
<DIV><FONT size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2>&nbsp;&nbsp;&nbsp; It will just take a while and=20
probably&nbsp;a fresh set of participants to make the adjustment. =
</FONT></DIV>
<DIV><FONT size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2>&nbsp;&nbsp;&nbsp; I still buy apples by the pound =
but to=20
prepare for the changeover;&nbsp;a Newton of apples will be one apple. =
Right=20
?</FONT></DIV>
<DIV><FONT size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2>Yt, Dave Webster, Kentville</FONT></DIV>
<DIV><FONT size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2>&nbsp;&nbsp;&nbsp; </FONT>&nbsp;</DIV>
<BLOCKQUOTE=20
style=3D"BORDER-LEFT: #000000 2px solid; PADDING-LEFT: 5px; =
PADDING-RIGHT: 0px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px"=20
dir=3Dltr>
  <DIV style=3D"FONT: 10pt arial">----- Original Message ----- </DIV>
  <DIV=20
  style=3D"FONT: 10pt arial; BACKGROUND: #e4e4e4; font-color: =
black"><B>From:</B>=20
  <A title=3Dpatrick.kelly@dal.ca =
href=3D"mailto:patrick.kelly@dal.ca">Patrick=20
  Kelly</A> </DIV>
  <DIV style=3D"FONT: 10pt arial"><B>To:</B> <A =
title=3Dnaturens@chebucto.ns.ca=20
  href=3D"mailto:naturens@chebucto.ns.ca">naturens@chebucto.ns.ca</A> =
</DIV>
  <DIV style=3D"FONT: 10pt arial"><B>Sent:</B> Saturday, September 22, =
2012 11:28=20
  AM</DIV>
  <DIV style=3D"FONT: 10pt arial"><B>Subject:</B> Re: [NatureNS] =
Correction; Fw:=20
  Velocity of light</DIV>
  <DIV><BR></DIV>I'm not sure I see the confusion arises over the kg =
being a=20
  unit of mass. I just covered this in my last astronomy class and why =
people=20
  use the words mass and weight interchangeably when they are two =
totally=20
  different things. Mass is a measure of how much matter an object =
contains. You=20
  measure mass with a scale. A 1 kg bag of sugar has the same mass here =
as well=20
  as on the Moon, as on a scale you would still need a 1kg mass to =
balance it.
  <DIV><BR></DIV>
  <DIV>Weight is a force, not a measure of mass. The problem is not =
helped when=20
  people still use the English unit of "pound" for both weight and mass. =
The=20
  English system unit of mass is the slug, not the pound. Your weight is =
the=20
  force of gravity acting on your mass and depends on your mass, the =
mass of the=20
  Earth and the radius of the Earth. if you are standing on the Moon =
(different=20
  mass and radius) you will "weigh" less because the gravitational force =
is=20
  less. If you stood on a doctor's scale on the Moon you would find that =
your=20
  mass is the same as it is on Earth.</DIV>
  <DIV><BR></DIV>
  <DIV>In the metric system, the unit of force is the Newton (the symbol =
is N).=20
  1 N is the force that is required to accelerate a 1 kg mass at the =
rate of 1=20
  m/s/s. (i.e. Force =3D mass X acceleration).&nbsp;</DIV>
  <DIV><BR></DIV>
  <DIV>At the surface of the Earth, the gravitational force =3D G x m x =
M / (r x=20
  r), where G is the gravitational constant, m is the mass of a small =
object=20
  (like a person), M is the mass of the Earth and r is the radius of the =

  Earth.</DIV>
  <DIV><BR></DIV>
  <DIV>If you drop that small object, this force will also produce an=20
  acceleration (because&nbsp;Force =3D mass X acceleration). So F =3D m =
x a. Since=20
  the force comes from gravity:</DIV>
  <DIV><BR></DIV>
  <DIV>m x a =3D&nbsp;G x m x M / (r x r)</DIV>
  <DIV><BR></DIV>
  <DIV>Note that since the small object is on both sides of the =
equation, you=20
  can cancel it, and thus you get:</DIV>
  <DIV><BR></DIV>
  <DIV>a =3D&nbsp;G x M / (r x r)</DIV>
  <DIV><BR></DIV>
  <DIV>This acceleration gets a special symbol, g, and has a value of =
9.8 m/s/s=20
  (which you can round of to 10 m/s/s). This is the rate at which =
<B>all</B>=20
  objects at the surface will fall (in a vacuum). If you go to the Moon, =
since M=20
  and r are different the surface gravity there is much lower, 1.7 m/s/s =
of=20
  about 1/5 that of the Earth.</DIV>
  <DIV><BR></DIV>
  <DIV>You can also use the surface gravity as a quick way to calculate =
your=20
  "weight" by multiplying your mass (in kg) by g. A 1 kg mass has a =
"weight" of=20
  9.8 N and a person such as myself with a mass of about 100 kg would =
have a=20
  weight of 980 N. Thus a proper metric scale would NOT be graduated in =
kg, but=20
  in Newtons. I expect there are two reasons they don't. One is that =
most people=20
  would freak if their "weight" appeared to be 10 times what they =
thought it=20
  was, and secondly, since they assume you are using the scale at the =
Earth's=20
  surface, they have "converted" the force back into "mass". Just don't =
take it=20
  to the Moon and expect it to work properly!</DIV>
  <DIV><BR></DIV>
  <DIV>Pat</DIV>
  <DIV><BR></DIV>
  <DIV>PS: For those who are curious, a mass of 1 slug has a weight at =
the=20
  Earth's surface of 32 pounds.</DIV>
  <DIV><BR></DIV>
  <DIV><BR></DIV>
  <DIV><BR>
  <DIV>
  <DIV><BR></DIV>
  <DIV>The kg a unit oef mass&nbsp;<BR>
  <DIV>
  <DIV>On Sep 22, 2012, at 9:58 AM, David &amp; Alison Webster =
wrote:</DIV><BR=20
  class=3DApple-interchange-newline>
  <BLOCKQUOTE type=3D"cite">
    <DIV>Hi Fred &amp; All,=20
    =
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&=
nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Sept=20
    22, 2012<BR>&nbsp;&nbsp;Explanations of weight/mass usually resemble =

    inconsistent confessions obtained by torture but I guess that is ok=20
    now.<BR><BR>&nbsp;&nbsp;It seems logical to me that weight should be =
treated=20
    as a special case of F=3Dma where a in this case is g and F is =
measured by=20
    exerting an equal and opposite force upward to keep the mass from=20
    falling.<BR><BR>&nbsp;&nbsp;One could then determine the magnitude =
of mass=20
    as F/g and then proceed to work out units of momentum, inertia etc =
from=20
    there.<BR><BR>&nbsp;&nbsp;But unfortunately kg has been defined (or =
perhaps=20
    redefined) as a unit of mass which leads to everything being a =
hopeless=20
    muddle.<BR><BR>&nbsp;&nbsp;I would try to reform the system of units =
dealing=20
    with weight, mass and distance but I am tied up this =
afternoon.<BR><BR>Yt,=20
    Dave Webster, Kentville<BR>----- Original Message ----- From: "Fred=20
    Schueler" &lt;<A=20
    href=3D"mailto:bckcdb@istar.ca">bckcdb@istar.ca</A>&gt;<BR>To: =
&lt;<A=20
    =
href=3D"mailto:naturens@chebucto.ns.ca">naturens@chebucto.ns.ca</A>&gt;<B=
R>Sent:=20
    Friday, September 21, 2012 9:19 PM<BR>Subject: Re: [NatureNS] =
Correction;=20
    Fw: Velocity of light<BR><BR><BR>
    <BLOCKQUOTE type=3D"cite">Quoting David &amp; Alison Webster &lt;<A=20
      =
href=3D"mailto:dwebster@glinx.com">dwebster@glinx.com</A>&gt;:<BR></BLOCK=
QUOTE>
    <BLOCKQUOTE type=3D"cite"><BR></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">
      <BLOCKQUOTE type=3D"cite">I just dug out my 1st yr Physics (Weber, =
White=20
        &amp; Manning, 1952) and &nbsp;they consistently refer to 'speed =
of=20
        light' as opposed to 'velocity &nbsp;of light'. Four other =
sources=20
        (1941, 1948, ~1965 &amp;1962) have =
velocity.<BR></BLOCKQUOTE></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite"><BR></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">* indeed, it would be ineffective to purge =

      society, or even &nbsp;literature, of all who misuse =
speed/velocity or=20
      weight/mass. Or, to &nbsp;bring it closer to natural history, all =
who=20
      refer to nonhemipterans as &nbsp;"bugs."<BR></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite"><BR></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">fred.<BR></BLOCKQUOTE>
    <BLOCKQUOTE=20
    =
type=3D"cite">=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D<BR></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite"><BR></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">
      <BLOCKQUOTE type=3D"cite">----- Original Message ----- From: =
"David &amp;=20
        Alison Webster" &lt;<A=20
        =
href=3D"mailto:dwebster@glinx.com">dwebster@glinx.com</A>&gt;<BR></BLOCKQ=
UOTE></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">
      <BLOCKQUOTE type=3D"cite">To: &lt;<A=20
        =
href=3D"mailto:NatureNS@chebucto.ns.ca">NatureNS@chebucto.ns.ca</A>&gt;<B=
R></BLOCKQUOTE></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">
      <BLOCKQUOTE type=3D"cite">Sent: Friday, September 21, 2012 7:44=20
      PM<BR></BLOCKQUOTE></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">
      <BLOCKQUOTE type=3D"cite">Subject: Velocity of=20
    light<BR></BLOCKQUOTE></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">
      <BLOCKQUOTE type=3D"cite"><BR></BLOCKQUOTE></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">
      <BLOCKQUOTE type=3D"cite"><BR></BLOCKQUOTE></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">
      <BLOCKQUOTE type=3D"cite">
        <BLOCKQUOTE type=3D"cite">Dear All,=20
          =
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&=
nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Sept=20
          21, 2012<BR></BLOCKQUOTE></BLOCKQUOTE></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">
      <BLOCKQUOTE type=3D"cite">
        <BLOCKQUOTE type=3D"cite">&nbsp;The recent discussion about =
transmission=20
          of electricity, reading &nbsp;of HEAT and reading some of =
Energy...=20
          brings to the forefront a &nbsp;question that has nagged me =
for=20
          decades. Perhaps someone can=20
    clarify.<BR></BLOCKQUOTE></BLOCKQUOTE></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">
      <BLOCKQUOTE type=3D"cite">
        <BLOCKQUOTE =
type=3D"cite"><BR></BLOCKQUOTE></BLOCKQUOTE></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">
      <BLOCKQUOTE type=3D"cite">
        <BLOCKQUOTE type=3D"cite">&nbsp;In the typical elementary =
physics text=20
          we are told that velocity &nbsp;is a vector quantity, and to =
quote one=20
          text "velocity... may be &nbsp;defined as the rate of change =
of=20
          position in a given direction". &nbsp;But "In cases where the=20
          direction of motion does not require to be &nbsp;considered , =
the term=20
          speed is employed to express the rate of=20
        &nbsp;travelling."<BR></BLOCKQUOTE></BLOCKQUOTE></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">
      <BLOCKQUOTE type=3D"cite">
        <BLOCKQUOTE =
type=3D"cite"><BR></BLOCKQUOTE></BLOCKQUOTE></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">
      <BLOCKQUOTE type=3D"cite">
        <BLOCKQUOTE type=3D"cite">&nbsp;Based on the above I would think =
that=20
          the rate of movement of &nbsp;light should be called speed, =
i.e. speed=20
          of light but I think it is &nbsp;always called=20
      velocity.<BR></BLOCKQUOTE></BLOCKQUOTE></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">
      <BLOCKQUOTE type=3D"cite">
        <BLOCKQUOTE type=3D"cite">For example, if light from the sun is=20
          reflected from two 45o &nbsp;mirrors then a beam of light =
could be=20
          directed from the earth back &nbsp;to the sun and, the =
velocity would=20
          then be minus 3 x 10^10 cm/sec. &nbsp;Or if variously =
scattered or=20
          reflected then the velocity, relative &nbsp;to the initial sun =
to=20
          earth direction, would always be less than 3 &nbsp;X 10^10 and =
after=20
          several reflections might be=20
zero.<BR></BLOCKQUOTE></BLOCKQUOTE></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">
      <BLOCKQUOTE type=3D"cite">
        <BLOCKQUOTE =
type=3D"cite"><BR></BLOCKQUOTE></BLOCKQUOTE></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">
      <BLOCKQUOTE type=3D"cite">
        <BLOCKQUOTE type=3D"cite">&nbsp;Is there some good reason why =
the speed=20
          of light is termed &nbsp;velocity of light ? Or is it called =
velocity=20
          because the textbook &nbsp;authors forget what they said in =
chapter=20
          one by the time they write &nbsp;chaper eleven ? (And they all =
copy=20
          from each other)<BR></BLOCKQUOTE></BLOCKQUOTE></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">
      <BLOCKQUOTE type=3D"cite">
        <BLOCKQUOTE type=3D"cite">Yt, Dave Webster,=20
      Kentville<BR></BLOCKQUOTE></BLOCKQUOTE></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">
      <BLOCKQUOTE type=3D"cite"><BR></BLOCKQUOTE></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">
      <BLOCKQUOTE type=3D"cite"><BR></BLOCKQUOTE></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite"><BR></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite"><BR></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite"><BR></BLOCKQUOTE>
    <BLOCKQUOTE=20
      =
type=3D"cite">-----------------------------------------------------------=
-<BR></BLOCKQUOTE>
    <BLOCKQUOTE=20
      =
type=3D"cite">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Frederick =
W.=20
      Schueler &amp; Aleta Karstad<BR></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">Bishops Mills Natural History Centre - <A=20
      =
href=3D"http://pinicola.ca/bmnhc.htm">http://pinicola.ca/bmnhc.htm</A><BR=
></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">Mudpuppy Night in Oxford Mills - <A=20
      =
href=3D"http://pinicola.ca/mudpup1.htm">http://pinicola.ca/mudpup1.htm</A=
><BR></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">Daily Paintings - <A=20
      =
href=3D"http://karstaddailypaintings.blogspot.com/">http://karstaddailypa=
intings.blogspot.com/</A><BR></BLOCKQUOTE>
    <BLOCKQUOTE=20
      =
type=3D"cite">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;South =
Nation=20
      Basin Art &amp; Science Book<BR></BLOCKQUOTE>
    <BLOCKQUOTE =
type=3D"cite">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<A=20
      =
href=3D"http://pinicola.ca/books/SNR_book.htm">http://pinicola.ca/books/S=
NR_book.htm</A><BR></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">&nbsp;&nbsp;&nbsp;RR#2 Bishops Mills, =
Ontario,=20
      Canada K0G 1T0<BR></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">&nbsp;&nbsp;presently in Cochrane &nbsp;-=20
      49.06274N 81.02415W -<BR></BLOCKQUOTE>
    <BLOCKQUOTE=20
      =
type=3D"cite">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;on=20
      the great Ontario Claybelt<BR></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">&nbsp;&nbsp;(613)299-3107 &lt;bckcdb at=20
      istar.ca&gt; <A=20
    =
href=3D"http://pinicola.ca/">http://pinicola.ca/</A><BR></BLOCKQUOTE>
    <BLOCKQUOTE=20
      =
type=3D"cite">-----------------------------------------------------------=
-<BR></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite"><BR></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite"><BR></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite"><BR></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">-----<BR></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">No virus found in this =
message.<BR></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">Checked by AVG - <A=20
      href=3D"http://www.avg.com">www.avg.com</A><BR></BLOCKQUOTE>
    <BLOCKQUOTE type=3D"cite">Version: 2012.0.2221 / Virus Database: =
2441/5278 -=20
      Release Date: =
09/19/12<BR></BLOCKQUOTE><BR><BR></DIV></BLOCKQUOTE></DIV><BR>
  <DIV apple-content-edited=3D"true"><SPAN=20
  style=3D"WIDOWS: 2; TEXT-TRANSFORM: none; TEXT-INDENT: 0px; =
BORDER-COLLAPSE: separate; FONT: medium Helvetica; WHITE-SPACE: normal; =
ORPHANS: 2; LETTER-SPACING: normal; COLOR: rgb(0,0,0); WORD-SPACING: =
0px; -webkit-border-horizontal-spacing: 0px; =
-webkit-border-vertical-spacing: 0px; =
-webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: =
auto; -webkit-text-stroke-width: 0px"=20
  class=3DApple-style-span>
  <DIV=20
  style=3D"WORD-WRAP: break-word; -webkit-nbsp-mode: space; =
-webkit-line-break: after-white-space"><SPAN=20
  style=3D"WIDOWS: 2; TEXT-TRANSFORM: none; TEXT-INDENT: 0px; =
BORDER-COLLAPSE: separate; FONT: medium Helvetica; WHITE-SPACE: normal; =
ORPHANS: 2; LETTER-SPACING: normal; COLOR: rgb(0,0,0); WORD-SPACING: =
0px; -webkit-border-horizontal-spacing: 0px; =
-webkit-border-vertical-spacing: 0px; =
-webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: =
auto; -webkit-text-stroke-width: 0px"=20
  class=3DApple-style-span>
  <DIV=20
  style=3D"WORD-WRAP: break-word; -webkit-nbsp-mode: space; =
-webkit-line-break: after-white-space"><SPAN=20
  style=3D"WIDOWS: 2; TEXT-TRANSFORM: none; TEXT-INDENT: 0px; =
BORDER-COLLAPSE: separate; FONT: medium Helvetica; WHITE-SPACE: normal; =
ORPHANS: 2; LETTER-SPACING: normal; COLOR: rgb(0,0,0); WORD-SPACING: =
0px; -webkit-border-horizontal-spacing: 0px; =
-webkit-border-vertical-spacing: 0px; =
-webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: =
auto; -webkit-text-stroke-width: 0px"=20
  class=3DApple-style-span>
  <P style=3D"MARGIN: 0px"><FONT style=3D"FONT: 12px Courier" size=3D3=20
  face=3DCourier><BR=20
  =
class=3DApple-interchange-newline>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D</FONT></P>
  <P style=3D"MARGIN: 0px"><FONT style=3D"FONT: 12px Courier" size=3D3=20
  face=3DCourier>Patrick Kelly</FONT></P>
  <P style=3D"MARGIN: 0px"><FONT style=3D"FONT: 12px Courier" size=3D3=20
  face=3DCourier>Director of Computer Facilities</FONT></P>
  <P style=3D"MARGIN: 0px"><FONT style=3D"FONT: 12px Courier" size=3D3=20
  =
face=3DCourier>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D</FONT></P>
  <P style=3D"MARGIN: 0px"><FONT style=3D"FONT: 12px Courier" size=3D3=20
  face=3DCourier>Faculty of Architecture and Planning</FONT></P>
  <P style=3D"MARGIN: 0px"><FONT style=3D"FONT: 12px Courier" size=3D3=20
  face=3DCourier>Dalhousie University</FONT></P>
  <P style=3D"MARGIN: 0px"><FONT style=3D"FONT: 12px Courier" size=3D3=20
  =
face=3DCourier>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D</FONT></P>
  <P style=3D"MARGIN: 0px"><FONT style=3D"FONT: 12px Courier" size=3D3=20
  face=3DCourier>MAIL &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; =
&nbsp;=20
  &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;=20
  COURIER</FONT></P>
  <P style=3D"MARGIN: 0px"><FONT style=3D"FONT: 12px Courier" size=3D3 =
face=3DCourier>PO=20
  Box 15000 &nbsp; &nbsp; &nbsp; &nbsp;&nbsp;<SPAN=20
  class=3DApple-converted-space>&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; =
&nbsp;=20
  &nbsp; &nbsp;&nbsp;<SPAN =
class=3DApple-converted-space>&nbsp;</SPAN></SPAN>5410=20
  Spring Garden Road</FONT></P>
  <P style=3D"MARGIN: 0px"><FONT style=3D"FONT: 12px Courier" size=3D3=20
  face=3DCourier>Halifax, Nova Scotia B3H 4R2<SPAN=20
  class=3DApple-converted-space>&nbsp;</SPAN><SPAN=20
  class=3DApple-converted-space>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<SPAN=20
  class=3DApple-converted-space>&nbsp;</SPAN></SPAN>Halifax, Nova=20
Scotia</FONT></P>
  <P style=3D"MARGIN: 0px"><FONT style=3D"FONT: 12px Courier" size=3D3=20
  face=3DCourier>Canada<SPAN =
class=3DApple-converted-space>&nbsp;</SPAN><SPAN=20
  class=3DApple-converted-space>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; =
&nbsp; &nbsp;=20
  &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<SPAN=20
  class=3DApple-converted-space>&nbsp;</SPAN></SPAN>Canada</FONT></P>
  <P style=3D"MARGIN: 0px"><FONT style=3D"FONT: 12px Courier" size=3D3=20
  =
face=3DCourier>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D</FONT></P>
  <P style=3D"MARGIN: 0px"><FONT style=3D"FONT: 12px Courier" size=3D3=20
  face=3DCourier>Phone:(902) 494-3294<SPAN =
class=3DApple-converted-space>&nbsp;=20
  &nbsp;<SPAN =
class=3DApple-converted-space>&nbsp;</SPAN></SPAN>FAX:(902)=20
  423-6672<SPAN class=3DApple-converted-space>&nbsp;</SPAN><SPAN=20
  class=3DApple-converted-space>&nbsp;<SPAN=20
  class=3DApple-converted-space>&nbsp;</SPAN></SPAN>E-mail:<A=20
  =
href=3D"mailto:patrick.kelly@dal.ca">patrick.kelly@dal.ca</A></FONT></P>
  <P style=3D"MARGIN: 0px"><FONT style=3D"FONT: 12px Courier" size=3D3=20
  =
face=3DCourier>=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D</FONT></P></SPAN></DIV></SPAN></DIV></SPAN></DIV><BR></DIV><=
/DIV></DIV><A></A>
  <P align=3Dleft color=3D"#000000" avgcert??>No virus found in this=20
  message.<BR>Checked by AVG - <A=20
  href=3D"http://www.avg.com">www.avg.com</A><BR>Version: 2012.0.2221 / =
Virus=20
  Database: 2441/5278 - Release Date: =
09/19/12</P></BLOCKQUOTE></BODY></HTML>

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