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Index of Subjects --047d7b3435268b2bb604ca4072ae Content-Type: text/plain; charset=ISO-8859-1 Dave, Nothing you have said is incorrect. A vector is convenient to represent a quantity that has both a magnitude and direction. Speed is simply the magnitude (scalar portion) of a velocity vector. If we call the light vector C, The speed of light (3x10^8 m/s), denoted by c, is the magnitude of the light vector, or mathematically, ||C||. It is only necessary to treat light propagation as a vector if the math requires it. In many situations the speed suffices. Hope this illuminates the situation. Bruce On Fri, Sep 21, 2012 at 7:44 PM, David & Alison Webster <dwebster@glinx.com>wrote: > 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 > -- Bruce Stevens Maryvale, NS --047d7b3435268b2bb604ca4072ae Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Dave,<div><br></div><div>Nothing you have said is incorrect. A vector is co= nvenient to represent a quantity that has both a magnitude and direction. S= peed is simply the magnitude (scalar portion) of a velocity vector. If we c= all the light vector C, The speed of light (3x10^8 m/s), denoted by c, is t= he magnitude of the light vector, or mathematically, ||C||. It is only nece= ssary to treat light propagation as a vector if the math requires it. In ma= ny situations the speed suffices.=A0</div> <div><br></div><div>Hope this illuminates the situation.<div><br></div><div= >Bruce<br><br><div class=3D"gmail_quote">On Fri, Sep 21, 2012 at 7:44 PM, D= avid & Alison Webster <span dir=3D"ltr"><<a href=3D"mailto:dwebster@= glinx.com" target=3D"_blank">dwebster@glinx.com</a>></span> wrote:<br> <blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1p= x #ccc solid;padding-left:1ex">Dear All, =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 = =A0 =A0 =A0 =A0Sept 21, 2012<br> =A0 =A0The 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.<br> <br> =A0 =A0In the typical elementary physics text we are told that velocity is = a vector quantity, and to quote one text "velocity... may be defined a= s the rate of change of position in a given direction". But "In c= ases where the direction of motion does not require to be considered , the = term speed is employed to express the rate of travelling."<br> <br> =A0 =A0Based 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.<br> 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 ve= locity would then be minus 3 x 10^10 cm/sec. Or if variously scattered or r= eflected 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.<br> <br> =A0 =A0Is there some good reason why the speed of light is termed velocity = of light ? Or is it called velocity because the textbook authors forget wha= t they said in chapter one by the time they write chaper eleven ? (And they= all copy from each other)<br> Yt, Dave Webster, Kentville <br> </blockquote></div><br><br clear=3D"all"><div><br></div>-- <br>Bruce Steven= s<br>Maryvale, NS<br> </div></div> --047d7b3435268b2bb604ca4072ae--
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