[B0ycey]

Ok it's not perfect, but this seems better now.

[Potemkin]

Because when you're measuring velocity, you're not measuring speed, you're measuring speed in relation to a reference frame.

I think this is the crux of your misconception, anasawad. Both speed and velocity are measured in relation to a particular reference frame. How else would you measure speed? Mathematically speaking, velocity is a vector. Like all vectors, it has direction and magnitude. What do we call the magnitude of the velocity vector? We call it "speed". Saying that light has the same speed through a medium as through the vacuum but a slower velocity is meaningless. The magnitude of a velocity is the speed. If the velocity is less, then the speed is less by definition. As I said, your distinction between speed and velocity makes no sense to me.

[anasawad]

@Potemkin
Because the speed of light is independent of a reference frame. This is a special case actually where only this speed is independent of a reference frame. Thus when discussing it, a distinction must be made.

[Potemkin]

Because the speed of light is independent of a reference frame. This is a special case actually where only this speed is independent of a reference frame. Thus when discussing it, a distinction must be made.

No, it doesn't. All speed is measured in relation to a frame of reference; otherwise, how would we know what that speed is? The point is that, when we measure the speed of light in relation to a frame of reference, then we get the same answer no matter which frame of reference we use. It is in this sense, and only in this sense, that we say that the speed of light is independent of our frame of reference. It still has to be measured, of course, and it has to be measured in relation to some particular frame of reference. We just happen to get the same answer regardless of which frame of reference we happen to choose, that's all. I think you have misunderstood what the phrase "independent of a reference frame" actually means. It does not mean that we can measure its speed without using a frame of reference.

[Besoeker]

No. Its not different between different mediums.

Then why define it as speed in a vacuum if the medium makes no difference?

[anasawad]

No, but because it is independent thus meaning it doesn't change regardless of the reference frame. Then in this case it is important to make the distinction between speed and velocity. Which 'm sure why most physical laws dealing with these variations are worded, velocity (V), not speed (c) when in this topic.

Because velocity is measuring a vector, thus between 2 points, or as you described it, macroscopic. While speed is not, speed is displacement per unit of time and thus microscopic.



@Besoeker
Because in a vacuum, its not interacting with or propagating in anything thus speed and velocity of light are the same. But in a medium, its not the same, so they make the distinction.
Thats why its called velocity not speed when dealing with variations.


Here you go, an example of the sudden differentiation when talking about it in a medium between speed and velocity.

In a medium, light usually does not propagate at a speed equal to c; further, different types of light wave will travel at different speeds. The speed at which the individual crests and troughs of a plane wave (a wave filling the whole space, with only one frequency) propagate is called the phase velocity vp. An actual physical signal with a finite extent (a pulse of light) travels at a different speed. The largest part of the pulse travels at the group velocity vg, and its earliest part travels at the front velocity vf.

[Besoeker]

No, but because it is independent thus meaning it doesn't change regardless of the reference frame.

It is speed that is being defined.
Try to get your head round that and stop waffling.

[Decky]

What I don't understand is how a prism splits white light into its component colours but raindrops also do it to make a rainbow. Raindrops are not toblerone shaped so why do they do the same thing?

[B0ycey]

What I don't understand is how a prism splits white light into its component colours but raindrops also do it to make a rainbow. Raindrops are not toblerone shaped so why do they do the same thing?

Have you ever wondered why rainbows are arcs rather than straight?

[anasawad]

If even the law you tried to invoke as a proof for your argument agrees its velocity. And if all the explanatory pieces says velocity when talking about this subject. Then i can clearly and easily say, that its your positions that is bullshit and that you're the one who cant understand basic principles of physics.

[Besoeker]

If even the law you tried to invoke as a proof for your argument agrees its velocity. And if all the explanatory pieces says velocity when talking about this subject. Then i can clearly and easily say, that its your positions that is bullshit and that you're the one who cant understand basic principles of physics.

The definition of c is speed in a vacuum.
If, as you assert, the speed isn't different in another medium why would would you need to define c as being in a vacuum?
There is an obvious answer but you'll fudge it again.

[Decky]

Have you ever wondered why rainbows are arcs rather than straight?

I always assumed they were anchored down by the weight of the pot of gold at either end.

[Besoeker]

If even the law you tried to invoke as a proof for your argument agrees its velocity. And if all the explanatory pieces says velocity when talking about this subject. Then i can clearly and easily say, that its your positions that is bullshit and that you're the one who cant understand basic principles of physics.

Shame that you can't seem to condusct a discussion without resorting to judgemental and deprecating comments.
And claim that "you're the one who cant understand basic principles of physics."

Speed is a scalar quantity and that's what the topic title refers to. Not a vector.
Speed and direction give you a vector but, as has been correctly stated earlier by others , speed is the magnitude.

My work has been on design in the electrical field mostly on power electronic systems for industrial applications, some quite large.
Many included power transformers. You have to specify the vector group at the design stage. It's arrangement gets printed on the rating plate - magnitude and direction. Try googling Ddyn11. Or power factor correction? Have you been there?

So maybe, just maybe I understand a bit about vectors.........

I mentioned refractive index so here's a bit of GCSE physics for you:

Refractive index of a material is a measure of the change in speed of light as it passes from a vacuum (or air as an approximation) into the material.

n = v1/v2

In the equation above, v1 is the speed of light in a vacuum. The bigger the refractive index the slower the light travels in that material - i.e. the smaller v2 is.

[Hindsite]

B0ycey wrote:
Have you ever wondered why rainbows are arcs rather than straight?

It is because God made it that way.

God said, "This is the sign of the covenant which I am making between Me and you and every living creature that is with you, for all successive generations; I set My bow in the cloud, and it shall be for a sign of a covenant between Me and the earth. It shall come about, when I bring a cloud over the earth, that the bow will be seen in the cloud, and I will remember My covenant, which is between Me and you and every living creature of all flesh; and never again shall the water become a flood to destroy all flesh. When the bow is in the cloud, then I will look upon it, to remember the everlasting covenant between God and every living creature of all flesh that is on the earth."

Genesis 9:12-16

[anasawad]

@Besoeker
Read this part;
https://en.wikipedia.org/wiki/Speed_of_ ... n_a_medium
And focus on the terms used.

[Besoeker]

@Besoeker
Read this part;
https://en.wikipedia.org/wiki/Speed_of_ ... n_a_medium
And focus on the terms used.

From your own link:

In a medium, light usually does not propagate at a speed equal to c

Which is exactly what I stated a gozillion posts ago, the very point where you first disputed it.

From Scientific American:

In the case of a rainbow, when sunlight hits a raindrop it does not move as fast through the water as it does through the atmosphere, so it bends a little. The light then turns again as it moves out of the raindrop and back into the air at its original speed.

And you also quoted this:

In a medium, light usually does not propagate at a speed equal to c; further, different types of light wave will travel at different speeds.

[anasawad]

@Besoeker
For a start, you pretty much quoted the reason in which i have arguing about for all this time and you have been denying.
Propagation.
And in the same line your quote is in.

The speed at which the individual crests and troughs of a plane wave (a wave filling the whole space, with only one frequency) propagate is called the phase velocity

Then followed by this part:

The phase velocity is important in determining how a light wave travels through a material or from one material to another. It is often represented in terms of a refractive index. The refractive index of a material is defined as the ratio of c to the phase velocity

Basically, what 've been saying for hours.

It turns out that the part that the change is actually called more accurately a velocity not abstract speed because it lines up with what defines a velocity more than so with a speed, average speed is close but not as close a velocity definition. Who knew.

[Besoeker]

@Besoeker
For a start, you pretty much quoted the reason in which i have arguing about for all this time and you have been denying.
Propagation.
And in the same line your quote is in.


Then followed by this part:


Basically, what 've been saying for hours.

It turns out that the part that the change is actually called more accurately a velocity not abstract speed because it lines up with what defines a velocity more than so with a speed, average speed is close but not as close a velocity definition. Who knew.

Which part of this don't you get:

In a medium, light usually does not propagate at a speed equal to c

Why state it if it isn't usually true?
And I note that you have totally failed to address two simple points.
I'll repeat them for you.

Why is c, the SPEED of light defined as in a vacuum? If it was no different in any other medium it would not be necessary to specify the medium.
You have ignored the point about how refractive index is calculated.
And you have ignored the links I gave you.

Might I gently remind you that the topic is about the speed of light. Speed is rate of travel or of propagation through a medium in this context. So a simple question for you. Would the time light takes to travel one metre in a vacuum be exactly the same time it would take to travel through a metre of glass?

[anasawad]

@Besoeker
1- the topic is about the speed of light in absolute, i.e the constant.
2- I did answer why its said speed in a vacuum, because there is nothing to interact with in a vacuum, thus the speed of light would be the absolute one.
3- For the refractive index, i didn't ignore it, infact you ignored it mutliple times because the index is calculate in ratio of velocities. As i did clearly show.
The law is velocity over velocity in the older versions and c the constant over phase velocities in the newer terminology. Not speed over speed. velocity.
Which not very surprising doesn't fit your point thus you keep ignoring it and claim that 'm the one not answering.
4- obviously you will keep failing to understand, it says the speed it propagates. Its stated like this in all sources including your sources because the people writing them realize that the speed of light it self doesn't change but rather it appears to change when measuring it outside the microscopic realm because it would be taken on a larger distances and scales thus it wont be possible to calculate the delays in which light cease to exist in them when traveling long distances in mediums.


And note, ignored links you gave ? you haven't provided anything so far other than your words while i provided the sources that give the point 'm giving.

[Saeko]

Anasawad is correct. End of thread.