Heater
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Re: Snarky non-responses to questions

Fri Mar 10, 2017 5:42 am

I see what you mean.

I don't believe anyone cares.

The angle between the cop and the road is generally very small.

Taking the trig into the measurement would not make much difference.

If it was, the only conclusion would be that you are traveling faster than the radar says.

You are busted.

Better not argue about the trig, it only makes your case worse!
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Gavinmc42
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Re: Snarky non-responses to questions

Fri Mar 10, 2017 6:09 am

I care, wrong comprehensions for a long time, my world has been turned upside down.
Er, lucky I have never been booked in 30years.
Guess my argument for the magistrate would have been wrong?

Hmm surely you travel less distance so it it slower?
Never was good with that Johnny is on a train traveling at 50mph thingy.

Dig out my Khan Academy files, back to school for me.
Next you will tell me the speed of light is not constant.
Johnny is in space ship traveling at half light speed, he shines a red laser at a spaceship going the other way, what colour is the laser?
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Re: Snarky non-responses to questions

Fri Mar 10, 2017 6:33 am

Gavinmc42,
Johnny is in space ship traveling at half light speed, he shines a red laser at a spaceship going the other way, what colour is the laser?
Who is the observer in this question?
Memory in C++ is a leaky abstraction .

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Re: Snarky non-responses to questions

Fri Mar 10, 2017 7:38 am

I always google for the answer - however, sometimes its impossible to find what you are looking for in all the garbage google throws up, or I dont know which method is best - which is when I turn to the forums.

As for snarky responses - theres no need. If you wouldnt say it to someones face, dont put it on the internet either. If you have nothing useful to say, dont say anything. If you need clarification, ask nicely and dont attemt to belittle the OP. If you're wound up, go away and have a cup of tea before posting anything.

Is this not just common sense?

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Re: Snarky non-responses to questions

Fri Mar 10, 2017 7:48 am

Heater wrote:Gavinmc42,
Johnny is in space ship traveling at half light speed, he shines a red laser at a spaceship going the other way, what colour is the laser?
Who is the observer in this question?
I would assume it is Johhny, as he is the subject.

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Re: Snarky non-responses to questions

Fri Mar 10, 2017 9:55 am

Gavinmc42 wrote:Cop sits on side of road, aims off at angle to on coming traffic.
Doppler measures speed to cop in direct line, the long side of the triangle.
But the car is not following that line, it is going along the road.
As it gets closer the angle changes.
Is the car going faster than the indicated speed or slower?
It practice it normally doesn't matter because the cops will usually have set the speed at which one will be pulled-over, ticketed or prosecuted, above that margin for error. That also allows the legally required accuracy of a speedometer to be taken into account.

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Re: Snarky non-responses to questions

Fri Mar 10, 2017 10:04 am

I suggest that the people references Pythagoras et al read the book "Reality is not what it seems". Not only a good introduction to quantum gravity, but has some very interesting history chapters along the way.
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Re: Snarky non-responses to questions

Fri Mar 10, 2017 10:14 am

Imagine the cop was a long, long way from the road. The distance between him and the car would mainly be the distance between him and the car; the car's movement would make little difference to the distance between them and therefore the speed he measured would be smaller.

IIUC, dopler shift in light is not the same as in sound because the constant speed of light does not permit it. Instead it falls out of Maxwell's equasions and Relativity. It happens though; that's what red-shift is in astronomy. Again IIRC, the maths uses photon energy rather than wave frequency. However, unlike sound, which one can calculate in high-school, the dopler effect in light is university level stuff.

I'm calling time on this thread though. Please tie up loose ends and put an end to it. I'd rather not impose a lock because that always leaves people with esprit d'escalier. (Google it ;) )

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Re: Snarky non-responses to questions

Fri Mar 10, 2017 10:24 am

rurwin wrote:. I'd rather not impose a lock because that always leaves people with esprit d'escalier. (Google it ;) )
What search terms should I use ? :lol:
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Re: Snarky non-responses to questions

Fri Mar 10, 2017 12:07 pm

Pithagoras,
I would assume it is Johnny, as he is the subject.
In that case: red.
Memory in C++ is a leaky abstraction .

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bensimmo
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Re: Snarky non-responses to questions

Fri Mar 10, 2017 3:15 pm

The laser is red, it always will be, it's in its name 'red laser'*
What people observe the photons as may not be interpreted as red.
But the laser doesn't change.


*Unless it has the wrong label.


Imagine a Pi in a box...

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rpdom
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Re: Snarky non-responses to questions

Fri Mar 10, 2017 3:18 pm

bensimmo wrote:Imagine a Pi in a box...
Has it got a heatsink?

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Re: Snarky non-responses to questions

Fri Mar 10, 2017 3:18 pm

bensimmo wrote:The laser is red, it always will be, it's in its name 'red laser'*
What people observe the photons as may not be interpreted as red.
But the laser doesn't change.


*Unless it has the wrong label.


Imagine a Pi in a box...
I think it might depend on the speed the laser is travelling at. Or something.
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Re: Snarky non-responses to questions

Fri Mar 10, 2017 3:25 pm

jamesh wrote:
bensimmo wrote:The laser is red, it always will be, it's in its name 'red laser'*
What people observe the photons as may not be interpreted as red.
But the laser doesn't change.
*Unless it has the wrong label.
Imagine a Pi in a box...
I think it might depend on the speed the laser is travelling at. Or something.
... and the direction (towards or away from the observer - consider "red-shift" or "blue-shift" w.r.t. galaxy motions, and "why is it dark at night" not a silly question**)
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Re: Snarky non-responses to questions

Fri Mar 10, 2017 4:01 pm

FTrevorGowen wrote:
jamesh wrote:
bensimmo wrote:The laser is red, it always will be, it's in its name 'red laser'*
What people observe the photons as may not be interpreted as red.
But the laser doesn't change.
*Unless it has the wrong label.
Imagine a Pi in a box...
I think it might depend on the speed the laser is travelling at. Or something.
... and the direction (towards or away from the observer - consider "red-shift" or "blue-shift" w.r.t. galaxy motions, and "why is it dark at night" not a silly question**)
Trev.
** this old physicist recalling the start of an early 70's lecture.
The laser itself is still 'red', assuming no effect on the cavity, spherical things and vacuums and such like.

The Doppler shift on the observed frequency depending on who observes it would shift it into the UV. 650nm to something like 375nm @ half c.

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Re: Snarky non-responses to questions

Fri Mar 10, 2017 4:02 pm

FTrevorGowen wrote:
jamesh wrote:
bensimmo wrote:The laser is red, it always will be, it's in its name 'red laser'*
What people observe the photons as may not be interpreted as red.
But the laser doesn't change.
*Unless it has the wrong label.
Imagine a Pi in a box...
I think it might depend on the speed the laser is travelling at. Or something.
... and the direction (towards or away from the observer - consider "red-shift" or "blue-shift" w.r.t. galaxy motions, and "why is it dark at night" not a silly question**)
Trev.
** this old physicist recalling the start of an early 70's lecture.
https://youtu.be/gxJ4M7tyLRE

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Re: Snarky non-responses to questions

Fri Mar 10, 2017 4:40 pm

I'm told Johnny has a red laser. And he is traveling with it.

I'm also told the observer in the question is Johnny.

So, he sees it as red. No matter what speed he traveling.
Memory in C++ is a leaky abstraction .

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Re: Snarky non-responses to questions

Fri Mar 10, 2017 5:04 pm

Johnny's in a vacuum. Johnny cannot see the laser.
Unless it reflects off the spaceship.
Last edited by bensimmo on Fri Mar 10, 2017 5:38 pm, edited 1 time in total.

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CarlRJ
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Re: Snarky non-responses to questions

Fri Mar 10, 2017 5:07 pm

Gavinmc42 wrote:I like to think I am preforming [sic] a public service duty by staying in the fast lane on cruise just a fraction above the speed limit.
This stops speeders from crashing etc. I am saving their lives.
Now the Nanny state says I must keep over and stay out of that lane unless over taking or I will be booked.
You can talk pejoratively about "the Nanny state" in the very same paragraph where you boast about you personally forcing other drivers to drive at the speed that you deem appropriate? Who is being the nanny then?

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Re: Snarky non-responses to questions

Fri Mar 10, 2017 5:15 pm

I've kept out of this discussion, partly because it's destined to go round in circles, partly because I've not got anything useful to say, but mainly because you're all wrong
Gavinmc42 wrote:Johnny is in space ship traveling at half light speed, he shines a red laser at a spaceship going the other way, what colour is the laser?
I've got to nit-pick.
"traveling at half light speed" relative to who?
"a spaceship going the other way" how fast, relative to Johnny, and towards him or away from him (i.e. is it still in front of him, or has it already passed him?)
"what colour is the laser?" depends on whether he's looking at the light reflected of his window on its way out, or after it's reflected off the other spaceship.

So I'm going round the M25, not rushing 'cos I'm heading out to sort out my mother-in-law's non-problems and I really don't like going there.
There's a truck in the inside lane doing 60, I'm doing 65, there's a convenient large gap in the second and third lanes, so I pull out and mosey along not getting in anyone's way.
Some wazzock's doing about 75 behind me in the inside lane; he can see me, he can see the truck, he can see the gap behind me, but it's obvious he's wanting to pass me on the inside, screech up to the truck, pull out in front of me probably with two fingers in the air.

I've got two choices: ease off so there's enough room for him to do what he wants safely, or speed up just enough that I'm too close to the truck for him to pull out in front.
Two questions: What do you think I'll do? and why is the truck nearly always Polish?

Another question: what's all this got to do with the OP?

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Re: Snarky non-responses to questions

Fri Mar 10, 2017 5:21 pm

rurwin wrote:I'm calling time on this thread though. Please tie up loose ends and put an end to it. I'd rather not impose a lock because that always leaves people with esprit d'escalier. (Google it ;) )
Bah! Googling is so much work! Can't you just link to the definition of L'esprit de l'escalier for us? ;)

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Re: Snarky non-responses to questions

Fri Mar 10, 2017 5:39 pm

Heater wrote:I'm told Johnny has a red laser. And he is traveling with it.

I'm also told the observer in the question is Johnny.

So, he sees it as red. No matter what speed he traveling.
No, you're wrong:
Johnny can't see the laser as he's now blind from trying to look at it to find out it's colour.
(It's got to be suitably strong to be used for such calculations, either that or suitably strong to destroy the empires TIE Fighters)

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Re: Snarky non-responses to questions

Fri Mar 10, 2017 5:47 pm

I think you need to go to the appropriate forums to answer and find the correct solutions.

Try the governments website, they know the laws.
Try candleforums, they know light.
Also try the manufacturer of the laser as they made it and should know.

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rurwin
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Re: Snarky non-responses to questions

Fri Mar 10, 2017 6:04 pm

In order to make sense in this "discussion" the observer has to be Johnny and he has to be observing the reflection of his red laser from the oncoming spaceship. Why is anyone confused by that?

Now using a smattering of Special Relativity and Newton is all I'm capable of, but I make the relative velocities A+B/(1+AB/c^2) = c/(1 + 0.25c^2/c^2) = c/1.25 = 0.8c

So the wave-fronts hit the oncoming ship at 1.8 times the frequency and are then retransmitted in the opposite direction and reach the observer at (1.8)^2 of their original frequency. That's a factor of 3.24. So the wavelength appears to reduce by the same factor, turning a 850nm wave into 262nm. That's UVC which is harder than sunscreen is rated for.

This is the wrong physics to be using -- as I said before. So this may be entirely wrong.

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Re: Snarky non-responses to questions

Fri Mar 10, 2017 6:13 pm

Especially as an 850nm wave is infrared, so somebody made your red laser wrong, i would complain to the manufacturer.

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