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that has nagged me for decades. Perhaps someone can clarify.=0A>>>>=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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Patrick Kelly
Director of Computer Facilities
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Faculty of Architecture and Planning
Dalhousie University
=
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=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
MAIL COURIER
PO Box 15000 5410 Spring Garden Road
Halifax, Nova Scotia B3H 4R2 Halifax, Nova Scotia
Canada Canada
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Phone:(902) 494-3294 FAX:(902) 423-6672 =
E-mail:patrick.kelly@dal.ca
=
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------=_NextPart_000_0099_01CD98FF.5F28E350
Content-Type: text/html;
charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META content=3D"text/html; charset=3Diso-8859-1" =
http-equiv=3DContent-Type>
<META name=3DGENERATOR content=3D"MSHTML 8.00.6001.19298">
<STYLE></STYLE>
</HEAD>
<BODY=20
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 & All, =
=20
Sept 22,=20
2012</FONT></DIV>
<DIV><FONT size=3D2> 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> </DIV>
<DIV><FONT size=3D2> 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> </DIV>
<DIV><FONT size=3D2> Going to the moon to test this is =
expensive=20
and, in any case, one would need permission of the owners. It is =
more=20
convenient to consult a Quantitative Chemistry text. If 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> </DIV>
<DIV><FONT size=3D2> 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. </FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2></FONT><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2> It gets much worse if you use a =
weighing=20
system in which no reference 'mass' is concurrently 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> </DIV>
<DIV><FONT size=3D2> 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> </DIV>
<DIV><FONT size=3D2> 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 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> </DIV>
<DIV><FONT size=3D2> 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 ?=20
</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2> It will just take a while and=20
probably a fresh set of participants to make the adjustment. =
</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2> I still buy apples by the pound =
but to=20
prepare for the changeover; a Newton of apples will be one apple. =
Right=20
?</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>Yt, Dave Webster, Kentville</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2> </FONT> </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). </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 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 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 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 <BR>
<DIV>
<DIV>On Sep 22, 2012, at 9:58 AM, David & Alison Webster =
wrote:</DIV><BR=20
class=3DApple-interchange-newline>
<BLOCKQUOTE type=3D"cite">
<DIV>Hi Fred & All,=20
=
&=
nbsp; Sept=20
22, 2012<BR> Explanations of weight/mass usually resemble =
inconsistent confessions obtained by torture but I guess that is ok=20
now.<BR><BR> 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> 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> 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> 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" <<A=20
href=3D"mailto:bckcdb@istar.ca">bckcdb@istar.ca</A>><BR>To: =
<<A=20
=
href=3D"mailto:naturens@chebucto.ns.ca">naturens@chebucto.ns.ca</A>><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 & Alison Webster <<A=20
=
href=3D"mailto:dwebster@glinx.com">dwebster@glinx.com</A>>:<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
& Manning, 1952) and they consistently refer to 'speed =
of=20
light' as opposed to 'velocity of light'. Four other =
sources=20
(1941, 1948, ~1965 &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 literature, of all who misuse =
speed/velocity or=20
weight/mass. Or, to bring it closer to natural history, all =
who=20
refer to nonhemipterans as "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 &=20
Alison Webster" <<A=20
=
href=3D"mailto:dwebster@glinx.com">dwebster@glinx.com</A>><BR></BLOCKQ=
UOTE></BLOCKQUOTE>
<BLOCKQUOTE type=3D"cite">
<BLOCKQUOTE type=3D"cite">To: <<A=20
=
href=3D"mailto:NatureNS@chebucto.ns.ca">NatureNS@chebucto.ns.ca</A>><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; Sept=20
21, 2012<BR></BLOCKQUOTE></BLOCKQUOTE></BLOCKQUOTE>
<BLOCKQUOTE type=3D"cite">
<BLOCKQUOTE type=3D"cite">
<BLOCKQUOTE type=3D"cite"> The recent discussion about =
transmission=20
of electricity, reading of HEAT and reading some of =
Energy...=20
brings to the forefront a 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"> In the typical elementary =
physics text=20
we are told that velocity is a vector quantity, and to =
quote one=20
text "velocity... may be defined as the rate of change =
of=20
position in a given direction". But "In cases where the=20
direction of motion does not require to be considered , =
the term=20
speed is employed to express the rate of=20
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"> Based on the above I would think =
that=20
the rate of movement of light should be called speed, =
i.e. speed=20
of light but I think it is 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 mirrors then a beam of light =
could be=20
directed from the earth back to the sun and, the =
velocity would=20
then be minus 3 x 10^10 cm/sec. Or if variously =
scattered or=20
reflected then the velocity, relative to the initial sun =
to=20
earth direction, would always be less than 3 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"> Is there some good reason why =
the speed=20
of light is termed velocity of light ? Or is it called =
velocity=20
because the textbook authors forget what they said in =
chapter=20
one by the time they write 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"> Frederick =
W.=20
Schueler & 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"> South =
Nation=20
Basin Art & Science Book<BR></BLOCKQUOTE>
<BLOCKQUOTE =
type=3D"cite"> <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"> RR#2 Bishops Mills, =
Ontario,=20
Canada K0G 1T0<BR></BLOCKQUOTE>
<BLOCKQUOTE type=3D"cite"> presently in Cochrane -=20
49.06274N 81.02415W -<BR></BLOCKQUOTE>
<BLOCKQUOTE=20
=
type=3D"cite">  =
;on=20
the great Ontario Claybelt<BR></BLOCKQUOTE>
<BLOCKQUOTE type=3D"cite"> (613)299-3107 <bckcdb at=20
istar.ca> <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 =
=20
=20
COURIER</FONT></P>
<P style=3D"MARGIN: 0px"><FONT style=3D"FONT: 12px Courier" size=3D3 =
face=3DCourier>PO=20
Box 15000 <SPAN=20
class=3DApple-converted-space> =
=20
<SPAN =
class=3DApple-converted-space> </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> </SPAN><SPAN=20
class=3DApple-converted-space> <SPAN=20
class=3DApple-converted-space> </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> </SPAN><SPAN=20
class=3DApple-converted-space> =
=20
<SPAN=20
class=3DApple-converted-space> </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> =20
<SPAN =
class=3DApple-converted-space> </SPAN></SPAN>FAX:(902)=20
423-6672<SPAN class=3DApple-converted-space> </SPAN><SPAN=20
class=3DApple-converted-space> <SPAN=20
class=3DApple-converted-space> </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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