Closing speed vs relative speed for dummies

Post by Uncle Ben
On Feb 13, 2009, 9:51 am (EST), "Androcles"

Snivelling relativistic lying bastard trolls claim that c+v is not
the speed of anything or is a "closing speed", accusing
mathematicians
of not being able to distinguish a "closing speed" from a "relative
speed" (which, with all honesty, I readily own that I cannot -'

The Newspeak you refer to has been invented in or around the 50ties of the
twentieth century - Einstein did NOT take participate in that. However, you
are of course quite right that Andro got confused by the simple terms such
as c-v, but this appears to have happened WITHOUT the introduction of such
jargon. On the other hand, it is possible of course that he FIRST got
confused by that jargon, and next the reading of Einstein's paper was done
with confused eyes, and so the damage was irreversible...

Post by Uncle Ben
Thus in his delicate and tactful manner,
Androcles suggests that Einstein violates the 2nd Postulate of SR,
when actually Einstein is merely calculating the time of closure
between a light wave with speed c and a target moving at speed v. If
the target is moving away from the oncoming light beam, the distance
betweem them decreases at the rate c-v; if it is moving towards the
oncoming beam, the closing rate is c-v.

Me thinks you surely mean:
" If the target is moving away from the oncoming light beam, the distance
betweem them decreases at the rate c-v; if it is moving towards the oncoming
beam, the closing rate is c+v." ;-)

Moreover, if the target is moving away from a retreating lightbeam, the
distance betweem them increases at the rate c+v; if it is following the
retreating beam, the opening rate is c-v.

Not quite, see your own text just above; as you correctly stated initially,
*relative speed* is the speed of one object relative to another; and the
other object may be either a small object or a reference frame (even a
virtual one).
However, *speed* generally means the relative speed of one object wrt a
frame of reference.

Post by Uncle Ben
Gaileo's big year was 1605. Jump forward 300 years to 1905, leaving
Androcles behind, and Einstein is theorizing that distance and time
change their scales with motion so as to preserve the speed of light
between frames. This is where the difference between closing speed
and relative speed arises.

Not quite: "closing speed" is merely Newspeak for "relative speed", and some
good textbooks still correctly define "relative speed" without being
influenced by new jargon. Poor Androcles, I can understand that he got
confused! If you like to read more about it, I can give you a very good
reference from the Aus.J.P.

Post by Uncle Ben
Consider two light beams aimed at each other, each travelling at speed
c. The distance between their light fronts decreases at the rate 2c,
and this is the closing speed.

In my and Einstein's words: "relative speed".

Post by Uncle Ben
To compute their relative speed

In my and Einstein's words: "speed" (or, in the old English translation of
his 1905 paper, "velocity").

Post by Uncle Ben
starting with a Lorentz transformation
with frame speed c is complicated by a singularity in the
transformation. But the general result for sub-luminal speeds u and
v
(u+v) / (1 + uv/c^2)
does not have that singularity. The resulting formula for relative
speed in this case is
(c+c)/(1 + c*c/c^2), which simplfies easily to c.

Note: this only refers to the 1-dimensional case for aligned velocities.

Post by Uncle Ben
Androcles has recently omitted his signature complaint about
Einstein's calculations. Maybe the penny in the slot has finally
dropped. But don't count on it yet.

I don't think so. ;-)

Cheers,
Harald

Uncle Ben

2009-02-16 16:23:55 UTC

Post by Uncle Ben
On Feb 13, 2009, 9:51 am (EST), "Androcles"

Snivelling relativistic lying bastard trolls claim that c+v is not
the speed of anything or is a "closing speed", accusing
mathematicians
of not being able to distinguish a "closing speed" from a "relative
speed" (which, with all honesty, I readily own that I cannot -'

" If the target is moving away from the oncoming light beam, the distance
betweem them decreases at the rate c-v; if it is moving towards the oncoming
beam, the closing rate is c+v." ;-)
Moreover, if the target is moving away from a retreating lightbeam, the
distance betweem them increases at the rate c+v; if it is following the
retreating beam, the opening rate is c-v.

Post by Uncle Ben
Consider two light beams aimed at each other, each travelling at speed
c. The distance between their light fronts decreases at the rate 2c,
and this is the closing speed.

In my and Einstein's words: "relative speed".

Post by Uncle Ben
To compute their relative speed

In my and Einstein's words: "speed" (or, in the old English translation of
his 1905 paper, "velocity").

Note: this only refers to the 1-dimensional case for aligned velocities.

Post by Uncle Ben
Androcles has recently omitted his signature complaint about
Einstein's calculations. Maybe the penny in the slot has finally
dropped. But don't count on it yet.

I don't think so. ;-)
Cheers,
Harald

Thanks for your comment, Harry, and for catching the typo.

I find it much more confusion to use the same term for two results so
different as c and 2c ! But to each his own definition.

Uncle Ben

harry

2009-02-16 19:48:41 UTC

Post by Uncle Ben
On Feb 13, 2009, 9:51 am (EST), "Androcles"

Snivelling relativistic lying bastard trolls claim that c+v is not
the speed of anything or is a "closing speed", accusing
mathematicians
of not being able to distinguish a "closing speed" from a "relative
speed" (which, with all honesty, I readily own that I cannot -'

Post by Uncle Ben
Consider two light beams aimed at each other, each travelling at speed
c. The distance between their light fronts decreases at the rate 2c,
and this is the closing speed.

In my and Einstein's words: "relative speed".

Post by Uncle Ben
To compute their relative speed

In my and Einstein's words: "speed" (or, in the old English translation of
his 1905 paper, "velocity").

Note: this only refers to the 1-dimensional case for aligned velocities.

Post by Uncle Ben
Androcles has recently omitted his signature complaint about
Einstein's calculations. Maybe the penny in the slot has finally
dropped. But don't count on it yet.

I don't think so. ;-)
Cheers,
Harald

: Thanks for your comment, Harry, and for catching the typo.

: I find it much more confusion to use the same term for two results so
: different as c and 2c ! But to each his own definition.

: Uncle Ben

Hi Ben please read it again: in that example we use "speed"
(Geschwindigkeit) for c and "relative speed" for 2c; moreover, those who
don't use the new definition understand that it is in principle NOT very
different. In general we can always use the vectorial relative velocity
(c-v) which simply equals c for v=0 (in which case the "relative velocity"
or "closing velocity" equals "velocity", since our coordinate system happens
to be co-moving with the object).

To introduce a superfluous word that gives the impression that a relative
speed is somehow not relative or not a speed or something that obeys special
rules or logic (as Androcles thinks, and he is not the only one) is simply
misleading. Although in this case a word was added instead of removed, its
reducing effect on thinking is similar as with Newspeak, see
http://en.wikipedia.org/wiki/Newspeak.

Cheers,
Harald

Daryl McCullough

2009-02-17 16:03:33 UTC

harry says...

Post by harry
Not quite, see your own text just above; as you correctly stated initially,
*relative speed* is the speed of one object relative to another; and the
other object may be either a small object or a reference frame (even a
virtual one).
However, *speed* generally means the relative speed of one object wrt a
frame of reference.

Not quite: "closing speed" is merely Newspeak for "relative speed", and some
good textbooks still correctly define "relative speed" without being
influenced by new jargon.

What you are saying is not correct. "relative speed" is not the
same as "closing speed". If a textbook treats them the same, then
it is *not* a good textbook. It's a sloppy textbook.

Uncle Ben explained why not: In problems involving the
motion of two objects, A and B, there is a distinction between
(1) The rate of change of the distance between A and B, as
measured in some coordinate system S unrelated to the motion
of A and B. (This is what Ben called "the closing speed" between
A and B, as measured in coordinate system S).

(2) The rate of change of the distance between A and B, as
measured in a special coordinate system S in which A is at
rest. (This is what Ben called "the relative speed" between
A and B.)

(2) is a special case, and it's a very important special case.
In a collision between two cars, the important consideration
is the speed of one car as measured in the frame in which the
other car is at rest.

It is not Newspeak to introduce terminology that allows
*distinctions* to be made that could not be made otherwise.
*Failing* to make precise distinctions is the source of
very many crackpot errors. And the point of the inventors
of Newspeak in Orwell's novel was to *block* reasoning
by taking away the precision of language necessary to
conduct that reasoning. Using the same word, "relative speed"
to mean two different things is the sort of sloppy thinking
that Newspeak encouraged.

--
Daryl McCullough
Ithaca, NY

harry

2009-02-18 06:56:15 UTC

Post by Daryl McCullough
harry says...

Not quite: "closing speed" is merely Newspeak for "relative speed", and some
good textbooks still correctly define "relative speed" without being
influenced by new jargon.

What you are saying is not correct. "relative speed" is not the
same as "closing speed". If a textbook treats them the same, then
it is *not* a good textbook. It's a sloppy textbook.

Indeed "relative speed" is not the same as "closing speed", instead, closing
speed is a form of relative speed. Sorry if I wasn't clear!
(Note: if I say that a Toyota is a car, it does NOT mean that a car is a
Toyota!)

Post by Daryl McCullough
Uncle Ben explained why not: In problems involving the
motion of two objects, A and B, there is a distinction between
(1) The rate of change of the distance between A and B, as
measured in some coordinate system S unrelated to the motion
of A and B. (This is what Ben called "the closing speed" between
A and B, as measured in coordinate system S).

Indeed, and as I pointed out: Einstein, good textbooks and myself call that
"relative speed".

Post by Daryl McCullough
(2) The rate of change of the distance between A and B, as
measured in a special coordinate system S in which A is at
rest. (This is what Ben called "the relative speed" between
A and B.)

Indeed, and as I pointed out: Einstein, good textbooks and myself call that
form of relative speed simply "speed".

Post by Daryl McCullough
(2) is a special case, and it's a very important special case.
In a collision between two cars, the important consideration
is the speed of one car as measured in the frame in which the
other car is at rest.

Not necessarily: other important considerations can be for example the frame
in which the total centre of mass is in rest.

Post by Daryl McCullough
It is not Newspeak to introduce terminology that allows
*distinctions* to be made that could not be made otherwise.

Indeed. Apprently like Ben you did not understand my clarification that the
distinction already existed, nor did you read my pointing this out to him.

Post by Daryl McCullough
*Failing* to make precise distinctions is the source of
very many crackpot errors.

Yes indeed, sorry to see that you are misguided this time.

Post by Daryl McCullough
And the point of the inventors
of Newspeak in Orwell's novel was to *block* reasoning
by taking away the precision of language necessary to
conduct that reasoning.

Yes indeed, as I also explained to Ben in the next posting which you forgot
to read before jumping on this. :-)

Post by Daryl McCullough
Using the same word, "relative speed"
to mean two different things is the sort of sloppy thinking
that Newspeak encouraged.

Yes indeed, and not applicable here - as already explained.

Good luck,
Harald

Daryl McCullough

2009-02-19 01:45:36 UTC

harry says...

Indeed, and as I pointed out: Einstein, good textbooks and myself call that
"relative speed".

I disagree. I think it is bad terminology and very confusing.

The fact that Einstein called it that was, in my opinion, because
he was addressing an audience that only knew Galilean relativity,
in which "closing speed" and "relative speed" are the same.

Indeed, and as I pointed out: Einstein, good textbooks and myself call that
form of relative speed simply "speed".

That doesn't make any sense. If there are two cars that are both
moving, and I say "The speed of the first car is 100 kilometers
per hour", I *DON'T* mean "The speed of the first car, as measured
in a frame in which the other car is at rest." Nobody uses that
terminology. It doesn't make any sense.

If I say "the speed of the first car", I mean the speed as measured
in an implicit "lab frame". If it's just a physics problem ("A car
with a mass of 1000 kilograms moving 120 kilometers
per hour collides with a car of mass 1200 kilograms moving in the
opposite direction at 80 kilometers per hour") it doesn't matter
exactly what the "lab frame" is. For a real experiment, it is
often implicitly the frame in which the lab is at rest (which
is why it is called the "lab frame").

Besides "speed" (which is dependent on an implicit "lab frame"),
there are two other concepts: (1) The rate at which the distance
between the objects changes, as measured in the "lab frame", and
(2) the rate at which the distance between the objects changes,
as measured in the rest frame of one of the objects.

What do you call those two quantities? You want to call the
first one "relative speed", but then what do you call the
second quantity? It *ISN'T* "speed". Speed means "the rate
at which the distance of the car from the origin of the
lab coordinate system changes".

--
Daryl McCullough
Ithaca, NY

harry

2009-02-19 11:46:11 UTC

Post by Daryl McCullough
harry says...

Indeed, and as I pointed out: Einstein, good textbooks and myself call that
"relative speed".

I disagree. I think it is bad terminology and very confusing.

Sorry I didn't carefully read what you wrote, and now it becomes more
interesting. Indeed it is only the same for 1D problems (which appeard to be
the topic of this thread, but the general case must not be forgotten!).
However the speed as you define here above is again something different, and
perhaps the term "closing speed" would be appropriate for it, see below.

Post by Daryl McCullough
The fact that Einstein called it that was, in my opinion, because
he was addressing an audience that only knew Galilean relativity,
in which "closing speed" and "relative speed" are the same.

Probably the term "closing speed" was not yet invented. I don't recall
having ever come across that term in any publication of before 1950.

Indeed, and as I pointed out: Einstein, good textbooks and myself call that
form of relative speed simply "speed".

That doesn't make any sense.

It's correct for the 1D problems of this thread, but not in general - sorry
for the glitch. However evidently you are confused in more than one way, see
below.

Post by Daryl McCullough
If there are two cars that are both moving,

Which means that you consider both cars with reference to a frame in which
both are measured as moving, as in your example 1.

Post by Daryl McCullough
and I say "The speed of the first car is 100 kilometers
per hour"

That means in standard language: wrt your coordinate system in which both
cars are moving...

Post by Daryl McCullough
, I *DON'T* mean "The speed of the first car, as measured
in a frame in which the other car is at rest." Nobody uses that
terminology. It doesn't make any sense.

Nor do I. See my reply to your example 1 as well as further below.

Post by Daryl McCullough
If I say "the speed of the first car", I mean the speed as measured
in an implicit "lab frame".

Quite so; more generally, it's the speed as measured in our inertial
coordinate system of choice.

Post by Daryl McCullough
If it's just a physics problem ("A car
with a mass of 1000 kilograms moving 120 kilometers
per hour collides with a car of mass 1200 kilograms moving in the
opposite direction at 80 kilometers per hour") it doesn't matter
exactly what the "lab frame" is. For a real experiment, it is
often implicitly the frame in which the lab is at rest (which
is why it is called the "lab frame").
Besides "speed" (which is dependent on an implicit "lab frame"),
there are two other concepts: (1) The rate at which the distance
between the objects changes, as measured in the "lab frame", and
(2) the rate at which the distance between the objects changes,
as measured in the rest frame of one of the objects.

The rest frame of one of the objects is according to both classical physics
and SRT just another valid reference frame (if it is a sufficiently good
approximation of a Newtonian frame); a material "lab frame" is not preferred
for the description of physics (the PoR).

Post by Daryl McCullough
What do you call those two quantities?

Personally I call them both Doppler speeds, and I specify the used reference
frame if not already implicit from the description. I don't know if a
generally accepted term for a change-of-distance rate exists but I think
that "closing speed" would be a good term for such a speed. Anyway, in 3D,
NEITHER of your cases is generally equal to the absolute value of the vector
subtraction (c-v) which appeared to be the subject of this thread.

Post by Daryl McCullough
You want to call the
first one "relative speed", but then what do you call the
second quantity?

I don't "want" to call anything; instead I'm happy with the standard
textbook definitions that I learned and know how to apply.

Post by Daryl McCullough
It *ISN'T* "speed". Speed means "the rate
at which the distance of the car from the origin of the
lab coordinate system changes".

No, that is erroneous: textbooks define speed as ds/dt, as measured in a
coordinate system of choice. As speed is the derivative of the object's
position over time, the position of the origin is irrelevant for the
determination of speed.

Moreover, in 3D problems there is a big difference between the definition
you use and the one of textbooks: when an object passes at a distance by a
point such as the origin in your reference system, at the instant that the
velocity is perpendicular to the origin the distance doesn't change (thus
you would say that its speed is zero!) even if its speed ds/dt is constant.

And as a reminder: textbooks define "relative velocity" as the vector
subtraction of two velocities V_ba = V_b - V_a ; Einstein also correctly
applied that definition in 1905.

Best regards,
Harald

Androcles

2009-02-19 12:45:23 UTC

Post by Daryl McCullough
harry says...

Indeed, and as I pointed out: Einstein, good textbooks and myself call that
"relative speed".

I disagree. I think it is bad terminology and very confusing.

Sorry I didn't carefully read what you wrote, and now it becomes more
interesting. Indeed it is only the same for 1D problems (which appeard to
be the topic of this thread, but the general case must not be forgotten!).
However the speed as you define here above is again something different,
and perhaps the term "closing speed" would be appropriate for it, see
below.

Probably the term "closing speed" was not yet invented. I don't recall
having ever come across that term in any publication of before 1950.

Indeed, and as I pointed out: Einstein, good textbooks and myself call that
form of relative speed simply "speed".

That doesn't make any sense.

It's correct for the 1D problems of this thread, but not in general -
sorry for the glitch. However evidently you are confused in more than one
way, see below.

Post by Daryl McCullough
If there are two cars that are both moving,

Which means that you consider both cars with reference to a frame in which
both are measured as moving, as in your example 1.

Post by Daryl McCullough
and I say "The speed of the first car is 100 kilometers
per hour"

That means in standard language: wrt your coordinate system in which both
cars are moving...

Post by Daryl McCullough
, I *DON'T* mean "The speed of the first car, as measured
in a frame in which the other car is at rest." Nobody uses that
terminology. It doesn't make any sense.

Nor do I. See my reply to your example 1 as well as further below.

Post by Daryl McCullough
If I say "the speed of the first car", I mean the speed as measured
in an implicit "lab frame".

Quite so; more generally, it's the speed as measured in our inertial
coordinate system of choice.

The rest frame of one of the objects is according to both classical
physics and SRT just another valid reference frame (if it is a
sufficiently good approximation of a Newtonian frame); a material "lab
frame" is not preferred for the description of physics (the PoR).

Post by Daryl McCullough
What do you call those two quantities?

Personally I call them both Doppler speeds, and I specify the used
reference frame if not already implicit from the description. I don't know
if a generally accepted term for a change-of-distance rate exists but I
think that "closing speed" would be a good term for such a speed. Anyway,
in 3D, NEITHER of your cases is generally equal to the absolute value of
the vector subtraction (c-v) which appeared to be the subject of this
thread.

Post by Daryl McCullough
You want to call the
first one "relative speed", but then what do you call the
second quantity?

I don't "want" to call anything; instead I'm happy with the standard
textbook definitions that I learned and know how to apply.

Post by Daryl McCullough
It *ISN'T* "speed". Speed means "the rate
at which the distance of the car from the origin of the
lab coordinate system changes".

No, that is erroneous: textbooks define speed as ds/dt, as measured in a
coordinate system of choice. As speed is the derivative of the object's
position over time, the position of the origin is irrelevant for the
determination of speed.
Moreover, in 3D problems there is a big difference between the definition
you use and the one of textbooks: when an object passes at a distance by a
point such as the origin in your reference system, at the instant that the
velocity is perpendicular to the origin the distance doesn't change (thus
you would say that its speed is zero!) even if its speed ds/dt is constant.
And as a reminder: textbooks define "relative velocity" as the vector
subtraction of two velocities V_ba = V_b - V_a ; Einstein also correctly
applied that definition in 1905.
Best regards,
Harald

Bwahahahahahahahaha!
Pathetic!
You two dozy bastards don't know how to knot two ropes together
without a text book and a lab frame, and McCullough has his head
so far up his arse he doesn't want to find out.

Real lab frame:
Loading Image...

Daryl McCullough

2009-02-19 13:03:18 UTC

harry says...

Post by Daryl McCullough
If there are two cars that are both moving,
and I say "The speed of the first car is 100 kilometers
per hour"

That means in standard language: wrt your coordinate system in which both
cars are moving...

Right. It does *not* mean

Indeed, and as I pointed out: Einstein, good textbooks and myself call
that form of relative speed simply "speed".
Besides "speed" (which is dependent on an implicit "lab frame"),
there are two other concepts: (1) The rate at which the distance
between the objects changes, as measured in the "lab frame", and
(2) the rate at which the distance between the objects changes,
as measured in the rest frame of one of the objects.

Yes, of course the frame in which one particle is at rest is
a perfectly valid frame. Of course, the lab frame isn't preferred.
You can use whatever frame you like. But the point is to
be clear which one you are using, especially if you are switching
from the description in one frame to the description in another.

Post by Daryl McCullough
What do you call those two quantities?

Personally I call them both Doppler speeds,

Well, my point is that you have different concepts, it is confusing
to use the *same* term. And why introduce new terminology when
it doesn't resolve any ambiguities?

Post by harry
and I specify the used reference frame if not already implicit
from the description.

Well, I'm saying that's what "relative to A" or "relative to the
lab" is for. If I say the speed relative to A, I mean the speed
as measured in a frame in which A is at rest.

Post by harry
I don't know if a generally accepted term for a change-of-distance
rate exists but I think that "closing speed" would be a good term
for such a speed.

The use of "closing speed" clarifies that you are not talking
about speed as measured in the rest frame of one of the objects.

Post by harry
Anyway, in 3D, NEITHER of your cases is generally equal to the
absolute value of the vector subtraction (c-v) which appeared
to be the subject of this thread.

What do you mean? c-v is the closing speed between an object
traveling at speed v and a light signal traveling at speed c
in the same direction.

Post by Daryl McCullough
You want to call the
first one "relative speed", but then what do you call the
second quantity?

I don't "want" to call anything; instead I'm happy with the standard
textbook definitions that I learned and know how to apply.

When there is confusion (and there *is* in this case), it is
reasonable to introduce new terminology to help clarify the
confusion. That's exactly what is going on with the introduction
of the terminology "closing speed" and "relative speed".

Post by harry
And as a reminder: textbooks define "relative velocity" as the vector
subtraction of two velocities V_ba = V_b - V_a ; Einstein also correctly
applied that definition in 1905.

Yes, some people do use that convention, but it is a bad
convention, and the use of "closing speed" or "closing velocity"
is better. Why is it better? Because the use of "relative velocity"
is *confusing*. The word "relative" is already overloaded to mean
"relative to a coordinate system". Look at the name of the theory: the theory of
*RELATIVITY*. Where does that word come from? From the word "relative".
Some quantities, such as velocity, simultaneity, the length of
objects, etc. are relative to the coordinate system, or frame,
in which they are measured.

So someone learning relativity would expect that the use of the
word "relative" means "relative to some coordinate system". But
that is *not* what the vector subtraction V_ba means. It's not
velocity relative to any coordinate system. So it is misleading
and confusing to use the word "relative" here.

You don't actually have a counter-argument as to why the word
"relative velocity" is appropriate, other than the fact that
people have used that terminology in the past. So WHAT? Who
cares? As time goes on, terminology gets adjusted to become
more regularized. Definitions get tightened up. New terminology
is introduced to make distinctions that are awkward to make
with previous terminology. There is nothing sacred about original
terminology.

--
Daryl McCullough
Ithaca, NY

harry

2009-02-19 14:36:12 UTC

Post by Daryl McCullough
harry says...

Post by Daryl McCullough
If there are two cars that are both moving,
and I say "The speed of the first car is 100 kilometers
per hour"

That means in standard language: wrt your coordinate system in which both
cars are moving...

Right. It does *not* mean

Indeed, and as I pointed out: Einstein, good textbooks and myself call
that form of relative speed simply "speed".

Yes and you said:
">>> "The speed of the first car is 100 kilometers
">>> per hour"

Thus Einstein, good textbooks and both of us call that form of relative
speed simply "speed" - without the need to add "relative". Do you have a
problem with that?

Post by Daryl McCullough
Besides "speed" (which is dependent on an implicit "lab frame"),
there are two other concepts: (1) The rate at which the distance
between the objects changes, as measured in the "lab frame", and
(2) the rate at which the distance between the objects changes,
as measured in the rest frame of one of the objects.

The point for me is that when you are NOT switching, there is no need to
specify that you are not switching.

Post by Daryl McCullough
What do you call those two quantities?

Personally I call them both Doppler speeds,

Well, my point is that you have different concepts, it is confusing
to use the *same* term. And why introduce new terminology when
it doesn't resolve any ambiguities?

I agree, maybe you forgot to correct your question?

Post by harry
and I specify the used reference frame if not already implicit
from the description.

Well, I'm saying that's what "relative to A" or "relative to the
lab" is for. If I say the speed relative to A, I mean the speed
as measured in a frame in which A is at rest.

And I mean that when I say "as measured in frame that is co-moving with A".
As I don't have the habit to jump frames like a madman (just as I don't have
the habit to switch between cm and inches every 10 secs), that isn't a
burden.

Post by harry
I don't know if a generally accepted term for a change-of-distance
rate exists but I think that "closing speed" would be a good term
for such a speed.

The use of "closing speed" clarifies that you are not talking
about speed as measured in the rest frame of one of the objects.

Please specify if you think that "closing speed" means:

A. The rate at which the distance between two objects closes
or
B. The absolute value of the vectorial difference of the velocities of two
objects
or
C. (?)

Post by harry
Anyway, in 3D, NEITHER of your cases is generally equal to the
absolute value of the vector subtraction (c-v) which appeared
to be the subject of this thread.

What do you mean? c-v is the closing speed between an object
traveling at speed v and a light signal traveling at speed c
in the same direction.

I could not find a definition of "closing speed" in my textbooks. However,
it would be a great coincidence if objects travel exactly in the same
direction as a light signal - a physics term that is only applicable in 1D
would be of extremely limited use. Please specify above.

Post by Daryl McCullough
You want to call the
first one "relative speed", but then what do you call the
second quantity?

I don't "want" to call anything; instead I'm happy with the standard
textbook definitions that I learned and know how to apply.

"Relative speed" and "speed" already existed and were perfectly well
defined. I now concede that "closing speed" would be useful - as you suggest
above - to specify the rate of change of distance between two objects, in
particular for Doppler topics. Such a rate of distance change is however in
general (3D) NOT the same as the difference in velocities c-v.

Post by harry
And as a reminder: textbooks define "relative velocity" as the vector
subtraction of two velocities V_ba = V_b - V_a ; Einstein also correctly
applied that definition in 1905.

We must be precise especially about the choice of reference, but that is in
SRT a common problem - the introduction of new jargon can be
counterproductive, as in this case it evidently is:
- Already, and as you show yourself here above, "speed" was and still is
*defined* as implying "relative to a coordinate system". To alter the
meaning of one term in order to make it mean the same as an already existing
term is either madness or Newspeak.
- See Ben's postings in this thread, while promoting "closing speed" he
explains "Relative speed, the speed of one object relative to another" AND
"Relative speed, in short, is the speed of one object with respect to a
frame of reference in which the other object is at rest."
- See your postings here, you seem to think that a term that stands for "a
rate of change of distance" correctly conveys the general meaning of a
difference of two velocities - which is plainly ERRONEOUS...

Post by Daryl McCullough
Look at the name of the theory: the theory of
*RELATIVITY*. Where does that word come from? From the word "relative".
Some quantities, such as velocity, simultaneity, the length of
objects, etc. are relative to the coordinate system, or frame,
in which they are measured.

Sure. Many of them already were relative since Newton, and the physics terms
have been well defined, as explained.

Post by Daryl McCullough
So someone learning relativity would expect that the use of the
word "relative" means "relative to some coordinate system".

Not if that person had received basic physics at secondary school...

Post by Daryl McCullough
But
that is *not* what the vector subtraction V_ba means. It's not
velocity relative to any coordinate system. So it is misleading
and confusing to use the word "relative" here.

A DIFFERENCE between velocities is commonly called RELATIVE velocities,
while a common velocity in physics is ALWAYS relative to a coordinate
system. Thus there is nothing "confusing" or "misleading" about it.
Anyway, I feel no need to defend common standards, I'm happy with them. What
do you think of Seto's wish to introduce a certain "ratio" instead of a
speed, because he finds "lightspeed" misleading?

Post by Daryl McCullough
You don't actually have a counter-argument as to why the word
"relative velocity" is appropriate, other than the fact that
people have used that terminology in the past.

Nonsense and you just gave me one additional argument: if as you think, (and
something else would be misleading), "closing speed" means the rate at which
a distance between two objects closes, than that term can NOT be used to
replace "relative velocity" - the velocity of one object relative to another
as measured in a reference frame of choice.

Post by Daryl McCullough
So WHAT? Who
cares? As time goes on, terminology gets adjusted to become
more regularized. Definitions get tightened up. New terminology
is introduced to make distinctions that are awkward to make
with previous terminology. There is nothing sacred about original
terminology.

True I don't care much - only I feel sorry for those who got confused.
As I don't really care, and you certainly have access to good textbooks -
over and out! :-)

Harald

Daryl McCullough

2009-02-19 16:46:49 UTC

harry says...

Post by Daryl McCullough
harry says...

Post by Daryl McCullough
If there are two cars that are both moving,
and I say "The speed of the first car is 100 kilometers
per hour"

That means in standard language: wrt your coordinate system in which both
cars are moving...

Right. It does *not* mean

Indeed, and as I pointed out: Einstein, good textbooks and myself call
that form of relative speed simply "speed".

">>> "The speed of the first car is 100 kilometers
">>> per hour"
Thus Einstein, good textbooks and both of us call that form of relative
speed simply "speed" - without the need to add "relative". Do you have a
problem with that?

Just the fact that it contradicts your use of the word "speed"
to mean "The rate of change of the distance between A and B,
as measured in a special coordinate system S in which A is at
rest".

Post by Daryl McCullough
Yes, of course the frame in which one particle is at rest is
a perfectly valid frame. Of course, the lab frame isn't preferred.
You can use whatever frame you like. But the point is to
be clear which one you are using, especially if you are switching
from the description in one frame to the description in another.

The point for me is that when you are NOT switching, there is no need to
specify that you are not switching.

Right. If you are keeping to one frame, then you don't need to
use the phrase "relative to", because everything is implicitly
relative to the "lab frame". On the other hand, if you mean
relative to a *different* frame, *then* you use the phrase
"relative to".

The convention of calling the vector difference of two
velocities "relative velocity" is confusing because you
*aren't* switching a new frame, as the word "relative"
would imply.

"Velocity of B relative to a frame in which A is at rest"

is perfectly well-defined and unambiguous. "Velocity of B
relative to A" is a completely natural shortening of that
phrase. It's very bizarre for "Velocity of B relative to
A" *not* to mean "Velocity of B relative to the rest frame
of A".

Post by Daryl McCullough
Well, I'm saying that's what "relative to A" or "relative to the
lab" is for. If I say the speed relative to A, I mean the speed
as measured in a frame in which A is at rest.

And I mean that when I say "as measured in frame that is co-moving with A".

But if you say "velocity of B relative to A", it *sounds* like that's
what you mean.

Post by harry
As I don't have the habit to jump frames like a madman

You're being silly. You pick whatever frame is easiest
to analyze whatever it is that you want to analyze. A
complex problem may very involve more than one frame.

Your point about the ambiguity of "closing speed" is perfectly
correct. I was indeed making a stupid mistake. The time derivative
of the distance between objects is not the same thing as the
absolute value of the vectorial difference of the velocities.
Calling the latter "closing velocity" only makes sense for problems
along a straight line.

So I do have to thank you for pointing that out. However, I
think that it still makes sense to use "relative velocity"
to mean "velocity of one object relative to the frame in which
the other object is at rest". That leaves no good term for
"the vectorial difference between two velocities". You have
convinced me that "closing velocity" is not an appropriate
term.

A DIFFERENCE between velocities is commonly called RELATIVE velocities

But I'm saying that in the context of Special Relativity, that
terminology is misleading and confusing. In the context of
Galilean Relativity, there is no difference between "The
vectorial difference between two velocities" and "The
velocity of one object as measured in a coordinate system
in which the other object is at rest". So the one term,
"relative velocity" is perfectly fine. In special relativity,
the two concepts diverge, so you must choose which one to call
"relative velocity".

Post by harry
Thus there is nothing "confusing" or "misleading" about it.

I explained why it is confusing. In Special Relativity, the
word "relative" means, in all other contexts, relative to a
*coordinate system*. For "relative velocity" *not* to mean that
is confusing.

--
Daryl McCullough
Ithaca, NY

harry

2009-02-20 09:36:30 UTC

Post by Daryl McCullough
harry says...

Post by Daryl McCullough
harry says...

Post by Daryl McCullough
If there are two cars that are both moving,
and I say "The speed of the first car is 100 kilometers
per hour"

That means in standard language: wrt your coordinate system in
which both cars are moving...

Right. It does *not* mean

Indeed, and as I pointed out: Einstein, good textbooks and myself
call that form of relative speed simply "speed".

">>> "The speed of the first car is 100 kilometers
">>> per hour"
Thus Einstein, good textbooks and both of us call that form of
relative speed simply "speed" - without the need to add "relative".
Do you have a problem with that?

Just the fact that it contradicts your use of the word "speed"
to mean "The rate of change of the distance between A and B,
as measured in a special coordinate system S in which A is at
rest".
However, speed generally means the relative speed of one object wrt a
frame of reference.

However - and as I already acknowledged - I erroneously copied your and
Ben's description of closing speed to mean the same as "relative speed"
while that is erroneous, and I even elaborated quite a lot on that topic. I
hope that important point to be useful for many others.

The point for me is that when you are NOT switching, there is no
need to specify that you are not switching.

More generally: relative to another object.
But as I don't want to waste more time on such fruitless discussions about
personal preference of which convention to follow and in which you even
started name calling, I will not comment further on that aspect. Note that I
generally reward name calling tactics with No Reply.

[...]

Post by Daryl McCullough
Your point about the ambiguity of "closing speed" is perfectly
correct. I was indeed making a stupid mistake. The time derivative
of the distance between objects is not the same thing as the
absolute value of the vectorial difference of the velocities.

Good that we clarified that!

Post by Daryl McCullough
Calling the latter "closing velocity" only makes sense for problems
along a straight line.
So I do have to thank you for pointing that out. However, I
think that it still makes sense to use "relative velocity"
to mean "velocity of one object relative to the frame in which
the other object is at rest". That leaves no good term for
"the vectorial difference between two velocities".

You finally discovered why I call it Newspeak: it suppresses a very useful
concept (although in a more subtle way than Orwell's Newspeak). However I
had misidentified "closing speed" as the cause - a special term for "rate of
change of distance" is certainly useful.

[...]

For you it is confusing and misleading while for me it is clarifying and
even enlightening.
Well, different brains are wired differently. :-)

Regards,
Harald

Edward Green

2009-02-20 02:17:53 UTC

On Feb 19, 8:03 am, ***@yahoo.com (Daryl McCullough)
wrote:
...

Post by Daryl McCullough
Yes, some people do use that convention, but it is a bad
convention, and the use of "closing speed" or "closing velocity"
is better. Why is it better? Because the use of "relative velocity"
is *confusing*. The word "relative" is already overloaded to mean
"relative to a coordinate system". Look at the name of the theory: the theory of
*RELATIVITY*. Where does that word come from? From the word "relative".
Some quantities, such as velocity, simultaneity, the length of
objects, etc. are relative to the coordinate system, or frame,
in which they are measured.
So someone learning relativity would expect that the use of the
word "relative" means "relative to some coordinate system". But
that is *not* what the vector subtraction V_ba means. It's not
velocity relative to any coordinate system. So it is misleading
and confusing to use the word "relative" here.
You don't actually have a counter-argument as to why the word
"relative velocity" is appropriate, other than the fact that
people have used that terminology in the past. So WHAT? Who
cares? As time goes on, terminology gets adjusted to become
more regularized. Definitions get tightened up. New terminology
is introduced to make distinctions that are awkward to make
with previous terminology. There is nothing sacred about original
terminology.

I claim I understand this issue perfectly well, but I kind of like
"relative velocity" for the simple vector subtraction nonetheless.
It's simply a frame dependent concept. "Velocity" itself is frame
dependent. So what?

The problem seems to be in conventional SR pedagogy the utility of
this concept is underplayed, and indeed many people reject it outright
(in my experience). But there is no need: vector velocity difference
is what you use to calculate a number of kinematic things in a given
frame.

Daryl McCullough

2009-02-20 03:12:15 UTC

Edward Green says...

Post by Edward Green
I claim I understand this issue perfectly well, but I kind of like
"relative velocity" for the simple vector subtraction nonetheless.
It's simply a frame dependent concept. "Velocity" itself is frame
dependent. So what?

My point is not that it is frame dependent, but that "relative to A"
usually means, in relativity theory, "as measured in A's rest frame".
So keeping with that convention, "velocity of B relative to A" would
mean "the velocity of B, as measured in A's frame".

--
Daryl McCullough
Ithaca, NY

harry

2009-02-20 12:42:10 UTC

Post by Daryl McCullough
Edward Green says...

Maybe in your book, but not in mine...

As Edward already wrote:
"The problem seems to be [that] in conventional SR pedagogy the utility of
this concept is underplayed".

But in fact it's worse: it's not just underplayed but - like in Orwell's
theme - one attempts to *suppress* a useful concept by an unnecessary change
of language (it's misleading to call that "keeping").

That's all.

Harald

Daryl McCullough

2009-02-20 13:10:27 UTC

harry says...

Post by harry
"The problem seems to be [that] in conventional SR pedagogy the utility of
this concept is underplayed".
But in fact it's worse: it's not just underplayed but - like in Orwell's
theme - one attempts to *suppress* a useful concept by an unnecessary change
of language (it's misleading to call that "keeping").

You are being ridiculous. There are two concepts, (1) the vector
difference of two velocities, as measured in the same frame, and (2)
the velocity of one object, as measured in the frame of the other
object. If it is "Orwellian" to have only a phrase meaning (2),
and no convenient phrase meaning (1), then why isn't the other way
around "Orwellian", as well?

To say that "relative velocity" always meant (1) is not very
persuasive, since (1) and (2) mean the same thing in Galilean
physics.

--
Daryl McCullough
Ithaca, NY

harry

2009-02-20 14:22:21 UTC

Post by Daryl McCullough
harry says...

Post by harry
"The problem seems to be [that] in conventional SR pedagogy the
utility of this concept is underplayed".
But in fact it's worse: it's not just underplayed but - like in
Orwell's theme - one attempts to *suppress* a useful concept by an
unnecessary change of language (it's misleading to call that
"keeping").

[snip namecalling]

Harald

j***@hotmail.com

2009-02-19 15:09:43 UTC

Post by Daryl McCullough
harry says...

Indeed, and as I pointed out: Einstein, good textbooks and myself call that
"relative speed".

I disagree. I think it is bad terminology and very confusing.

Probably the term "closing speed" was not yet invented. I don't recall
having ever come across that term in any publication of before 1950.

Indeed, and as I pointed out: Einstein, good textbooks and myself call
that
form of relative speed simply "speed".

That doesn't make any sense.

It's correct for the 1D problems of this thread, but not in general - sorry
for the glitch. However evidently you are confused in more than one way, see
below.

Post by Daryl McCullough
If there are two cars that are both moving,

Which means that you consider both cars with reference to a frame in which
both are measured as moving, as in your example 1.

Post by Daryl McCullough
and I say "The speed of the first car is 100 kilometers
per hour"

That means in standard language: wrt your coordinate system in which both
cars are moving...

Post by Daryl McCullough
, I *DON'T* mean "The speed of the first car, as measured
in a frame in which the other car is at rest." Nobody uses that
terminology. It doesn't make any sense.

Nor do I. See my reply to your example 1 as well as further below.

Post by Daryl McCullough
If I say "the speed of the first car", I mean the speed as measured
in an implicit "lab frame".

Quite so; more generally, it's the speed as measured in our inertial
coordinate system of choice.

Post by Daryl McCullough
What do you call those two quantities?

Personally I call them both Doppler speeds, and I specify the used reference
frame if not already implicit from the description.

Hello Harry nice to see you still vigorus trying to find solutions to
a SR problem, i am not sure you tackle them the right way though.

In Sweden we have the expression painting oneself into a corner and i
have the feeling that is what you are doing, in your attempt knoting
bananas together.

For us who are reasonably intelligent and logically inclined, we know
that your concept of doppler speed is simply good ol Newtonian c-v and
c+v, but you are a relativist and can not use those terms, because of
your beleif system based on measure theology.

Do you know how stupid doppler speed really sound, the term is
relative speed in the Newtonian vocabulary and it is c+v and c-v.

The way i see it *NOW* SRian slowly turn to accept the Newton laws of
motion. The problem is on they way they have to invent a terminology
that do not resemble of relative speed, so they will invent things
like doppler speed and start to try knot bananas together unfortunatly
it will not work that good.

Because as anyone knows a spatial magnitude is the same in both
direction, A->B = B->A. And their theory says it is not, so now they
will try to find away to climb that hinder.

Post by harry
I don't know if a
generally accepted term for a change-of-distance rate exists but I think
that "closing speed" would be a good term for such a speed.

Here you can see Harry trying real hard to think up new terminology,
like change of distance rate, a reasonably intelligent person can now
see Harry's next move.

He will introduce the term doppler distorted spatial magnitudes within
his theory, this is all to confuse for the reader from the fact that
he have Newton's background space, but still want to play the SR game,
using doppler speed, doppler magnitudes instead of good ol c+v and c-v
because as everyone knows there is no such thing as a doppler
distorted length in Newtons theory, only plain doppler effect things
remain what they are regardless *APPEARANCE*.

So now we most conclude how Harry wont to go on keep playing his game
first he must somehow get rid of length contraction *OUCH* that one
really did hurt. What about the time dilation looks like he can keep
playing the bubbleboy game there i think.

But now to the critical issue that relativity totally is dependent on.
It seem *OH MY GOSH* that Harry have abandoned the invariance of light
travel thru space, *GEESH THAT ONE REALLY HURT*.

Androcles is it really so that they finally accepted there is more
lightpulses in one direction than the other?

Did they really accept c+v and c-v but trying to come up with new
terminology to escape the shame and their embarresment, we should
really cork up a bottle and celebrate those bold relativists who
travelled so far noone travelled before.

To boldly go where someone gone before, cheers Newton cheers
Androcles.

JT

But as anyone read anyone of my thread

Anyway, in 3D,

Post by harry
NEITHER of your cases is generally equal to the absolute value of the vector
subtraction (c-v) which appeared to be the subject of this thread.

Post by Daryl McCullough
You want to call the
first one "relative speed", but then what do you call the
second quantity?

I don't "want" to call anything; instead I'm happy with the standard
textbook definitions that I learned and know how to apply.

Post by Daryl McCullough
It *ISN'T* "speed". Speed means "the rate
at which the distance of the car from the origin of the
lab coordinate system changes".

No, that is erroneous: textbooks define speed as ds/dt, as measured in a
coordinate system of choice. As speed is the derivative of the object's
position over time, the position of the origin is irrelevant for the
determination of speed.
Moreover, in 3D problems there is a big difference between the definition
you use and the one of textbooks: when an object passes at a distance by a
point such as the origin in your reference system, at the instant that the
velocity is perpendicular to the origin the distance doesn't change (thus
you would say that its speed is zero!) even if its speed ds/dt is constant.
And as a reminder: textbooks define "relative velocity" as the vector
subtraction of two velocities V_ba = V_b - V_a ; Einstein also correctly
applied that definition in 1905.
Best regards,
Harald- Dölj citerad text -
- Visa citerad text -

v***@icmf.inf.cu

2009-02-19 13:02:07 UTC

Post by Uncle Ben
On Feb 13, 2009, 9:51 am (EST), "Androcles"

Snivelling relativistic lying bastard trolls claim that c+v is not
the speed of anything or is a "closing speed", accusing
mathematicians
of not being able to distinguish a "closing speed" from a "relative
speed" (which, with all honesty, I readily own that I cannot -'

Post by Uncle Ben
Consider two light beams aimed at each other, each travelling at speed
c. The distance between their light fronts decreases at the rate 2c,
and this is the closing speed.

In my and Einstein's words: "relative speed".

Post by Uncle Ben
To compute their relative speed

In my and Einstein's words: "speed" (or, in the old English translation of
his 1905 paper, "velocity").

Note: this only refers to the 1-dimensional case for aligned velocities.

Post by Uncle Ben
Androcles has recently omitted his signature complaint about
Einstein's calculations. Maybe the penny in the slot has finally
dropped. But don't count on it yet.

I don't think so. ;-)
Cheers,
Harald

v***@icmf.inf.cu

2009-02-19 14:21:20 UTC

Post by Uncle Ben
On Feb 13, 2009, 9:51 am (EST), "Androcles"

Snivelling relativistic lying bastard trolls claim that c+v is not
the speed of anything or is a "closing speed", accusing
mathematicians
of not being able to distinguish a "closing speed" from a "relative
speed" (which, with all honesty, I readily own that I cannot -'

Hello Harald. I am very interested in the way you handle the concept
of "(inertial) reference frame" (IRF) here. You identify an IRF with a
"small object"? If that were the case, you associate a mass with an
IRF? Can you clear to me what do you mean by "virtual IRF" and "non-
virtual IRF"? At the end, in what I am really interested, is to know
about if every specific IRF (for example, the ECI one of the GPS) can
be used or not to describe the movement with respect to it of ANY
object of the whole Universe (for example, the Sun). As maybe you can
remember, since many years I am claiming here that a specific IRF can
be only the centre of mass one corresponding to some determined body
set (for the ECI of the GPS, the Earth and its operating artificial
satellites), and I am also claiming that the UNIQUE bodies whose
movement can be described using some specific IRF are the ones
belonging to its associated body set, the unique ones taken into
account when determining the centre of mass.

RVHG (Rafael Valls Hidalgo-Gato)

harry

2009-02-19 15:13:10 UTC

[...]

Post by v***@icmf.inf.cu

Post by Uncle Ben
Relative speed, the speed of one object relative to another, is a
different matter. In Galilean physics, there is no difference
between closing speed and relative speed, because distance and time
are on the same scale regardless of motion between the two frames
of reference. Relative speed, in short, is the speed of one object
with respect to a frame of reference in which the other object is
at rest.

Not quite, see your own text just above; as you correctly stated
initially, *relative speed* is the speed of one object relative to
another; and the other object may be either a small object or a
reference frame (even a virtual one).
However, *speed* generally means the relative speed of one object
wrt a frame of reference.

Hello Harald. I am very interested in the way you handle the concept
of "(inertial) reference frame" (IRF) here.

Hi Rafael,

In fact I did not define "inertial" here; tha should be specified or clear
from the context.
For example, a geostationary satellite is moving in a standard reference
frame such as the ECI frame (which is only truly "inertial" in GRT language)
but stationary in a co-rotating frame.

Post by v***@icmf.inf.cu
You identify an IRF with a
"small object"?

No, for example the ECI is identified with a big object (the Earth), but
nothing on the Earth is at rest in it. In the context of SRT, an "inertial
reference frame" is in reality a Newtonian frame, which is operationally
defined as non-rotating relative to the distant stars.

Post by v***@icmf.inf.cu
If that were the case, you associate a mass with an
IRF?

No, certainly not!

Post by v***@icmf.inf.cu
Can you clear to me what do you mean by "virtual IRF" and "non-
virtual IRF"?

A piece of matter that does not rotate relative to the stars is a real
frame.

Post by v***@icmf.inf.cu
At the end, in what I am really interested, is to know
about if every specific IRF (for example, the ECI one of the GPS) can
be used or not to describe the movement with respect to it of ANY
object of the whole Universe (for example, the Sun).

As hinted at above, for SRT the ECI frame is not an accurate reference
frame, certainyl not for long-term and long-distance measurements. Note that
all this is entirely besides the topic and I think we have discussed this in
the past.

Post by v***@icmf.inf.cu
As maybe you can
remember, since many years I am claiming here that a specific IRF can
be only the centre of mass one corresponding to some determined body
set (for the ECI of the GPS, the Earth and its operating artificial
satellites), and I am also claiming that the UNIQUE bodies whose
movement can be described using some specific IRF are the ones
belonging to its associated body set, the unique ones taken into
account when determining the centre of mass.

I know, and you surely remember that I don't think so. :-)
Thus I'm sorry but I won't discuss this again.

Best refgards,
Harlad

Edward Green

2009-02-16 16:16:57 UTC

On Feb 16, 9:32 am, Uncle Ben <***@greenba.com> wrote:

<...>

If the target is moving away from the oncoming light beam, the distance
betweem them decreases at the rate c-v; if it is moving towards the
oncoming beam, the closing rate is c-v.
Some of us have used the term "closing speed" for the factors quoted
above, and this has mystified Androcles. Closing speed is the rate of
change of the distance between two objects as they both move.

In a particular reference frame. Yes.

Not only Androcles is confused by this. Sometimes perfectly straight
relativists wax wroth when such expressions are used, insisting that
it is not correct relativistic velocity addition. Indeed it is not,
but in the correct context, neither is relativistic velocity addition
what one wants. In a fixed reference frame, calculation of time until
collision proceeds perfectly straightforwardly with purely Gallilean
concepts.

Androcles

2009-02-16 17:14:51 UTC

"Uncle Ben" <***@greenba.com> wrote in message news:518f5f95-8385-49c7-a268-***@r24g2000vbp.googlegroups.com...
On Feb 13, 2009, 9:51 am (EST), "Androcles"

Loading Image...

Now put up or shut up, fuckhead.

Uncle Ben

2009-02-16 18:27:00 UTC

Post by Uncle Ben
On Feb 13, 2009, 9:51 am (EST), "Androcles"

Androcles

2009-02-16 19:08:49 UTC

Post by Uncle Ben
On Feb 13, 2009, 9:51 am (EST), "Androcles"

The one showing both objects moving shows closing speed only.
The one showing the ship at rest shows relative speed, which is the
same as closing speed in that frame of reference.

No charge, dear one.

Uncle Ben

Cool. So the observer in the ship "at rest" both sees, and measures
using Doppler, the light approaching at c+v.

Now, fuckhead,
What kind of lunacy prompted the fuckin' moron Einstein, prince of
bullshit, to say
the speed of light from A to B is c-v,
the speed of light from B to A is c+v,
the "time" each way is the same, you ignorant fuckin' pervert?

PS. I expect Harald Van Lintel would like you to blow and kiss him,
at least you've found a fellow boneheaded poofter to suck up to, deer one.

Uncle Ben

2009-02-16 18:39:25 UTC

Post by Uncle Ben
On Feb 13, 2009, 9:51 am (EST), "Androcles"

There is a spaceship, a planet, and some light from the planet.
Choose any two of them. If both are moving, you can see only the
closing speed. If either is at rest, you can see both closing and
relative speed in that frame.

No charge, sweetheart.

Uncle Ben

Androcles

2009-02-16 19:18:23 UTC

Post by Uncle Ben
On Feb 13, 2009, 9:51 am (EST), "Androcles"

There is a spaceship, a planet, and some light from the planet.

=============================================
Sane people would say that was light from a star, but no matter.
Well done! You can read pictures. Next study "See Spot Run".

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Choose any two of them. If both are moving, you can see only the
closing speed. If either is at rest, you can see both closing and
relative speed in that frame.
=============================================
The speed being c+v.

No charge, sweetheart.

Uncle Ben
=============================================

For your next stage, you useless fuck,

What kind of lunacy prompted Einstein to say
the speed of light from A to B is c-v,
the speed of light from B to A is c+v,
the "time" each way is the same so that he could derive magic gamma?

Answer that correctly and I might let you kiss my arse.

Uncle Ben

2009-02-16 20:11:10 UTC

Androcles

2009-02-16 20:32:56 UTC

Post by Uncle Ben
Poor Androcles, stuck in the 19th century, cannot understand how
Albert Einstein, writing in the 20th, can write an equation
containing
the factors (c+v) and (c-v) and yet claim that the speed c is a
universal constant. Thus in his delicate and tactful manner,
Androcles suggests that Einstein violates the 2nd Postulate of SR,
when actually Einstein is merely calculating the time of closure
between a light wave with speed c and a target moving at speed v. If
the target is moving away from the oncoming light beam, the distance
betweem them decreases at the rate c-v; if it is moving towards the
oncoming beam, the closing rate is c+v.
Some of us have used the term "closing speed" for the factors quoted
above, and this has mystified Androcles. Closing speed is the rate of
change of the distance between two objects as they both move.
Closing
speed is certainly a rate of change of a distance, but in the given
frame of reference, there is no material object nor even a photon that
moves with that speed.

Poor Uncle Bonehead, still making silly assertions not commensurate
with the simple fact of relative motion, which he calls opening and
closing motion.
Einstein's theory of Special Closing and Opening Motion is an acceleration
free form of General Opening and Closing Motion.

Uncle Ben

2009-02-17 12:09:14 UTC

Post by Androcles

Post by Uncle Ben
Poor Androcles, stuck in the 19th century, cannot understand how
Albert Einstein, writing in the 20th, can write an equation
containing
the factors (c+v) and (c-v) and yet claim that the speed c is a
universal constant. Thus in his delicate and tactful manner,
Androcles suggests that Einstein violates the 2nd Postulate of SR,
when actually Einstein is merely calculating the time of closure
between a light wave with speed c and a target moving at speed v. If
the target is moving away from the oncoming light beam, the distance
betweem them decreases at the rate c-v; if it is moving towards the
oncoming beam, the closing rate is c+v.
Some of us have used the term "closing speed" for the factors quoted
above, and this has mystified Androcles. Closing speed is the rate
of
change of the distance between two objects as they both move.
Closing
speed is certainly a rate of change of a distance, but in the given
frame of reference, there is no material object nor even a photon that
moves with that speed.

I wrote my original post for dummies. I don't think I know how to
write one for idiots.

Uncle Ben

Androcles

2009-02-17 12:46:28 UTC

Post by Androcles

Post by Uncle Ben
Poor Androcles, stuck in the 19th century, cannot understand how
Albert Einstein, writing in the 20th, can write an equation
containing
the factors (c+v) and (c-v) and yet claim that the speed c is a
universal constant. Thus in his delicate and tactful manner,
Androcles suggests that Einstein violates the 2nd Postulate of SR,
when actually Einstein is merely calculating the time of closure
between a light wave with speed c and a target moving at speed v. If
the target is moving away from the oncoming light beam, the distance
betweem them decreases at the rate c-v; if it is moving towards the
oncoming beam, the closing rate is c+v.
Some of us have used the term "closing speed" for the factors quoted
above, and this has mystified Androcles. Closing speed is the rate
of
change of the distance between two objects as they both move.
Closing
speed is certainly a rate of change of a distance, but in the given
frame of reference, there is no material object nor even a photon that
moves with that speed.

I wrote my original post for dummies. I don't think I know how to
write one for idiots.
==============================================
Sure you do, Harald van lintel is hanging on your every word.

Why don't you teach the grinning ape how to derive magic gamma?

Begin with
the speed of light from A to B is c-v,
the speed of light from B to A is c+v,
the "time" each way is the same

and get to

gamma = 1/ sqrt( (c+v) * (c-v) /c^2)

so that t-vx/c^2 * magic gamma = tau, which is not a vector.

Show us all how smart you are, fuckhead.
"Easy: he did NOT say that. " -- cretin ***@epfl.ch

kenseto

2009-02-17 23:25:19 UTC

ou can have closing speed between two macroscopic objects. But you
can't have clocsing speed between an object and light. Why Because the
speed of light in any frame is constant and isotropic and the idea of
closing speed contradicts this SR postulate.

Ken Seto

2009-02-17 23:36:47 UTC