Laser weapons and recoil

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And laser rifles have recoil in EU...

And rightly so since photons do carry a momentum. This is how solar sails work. A laser and yes, even a flashlight, have a recoil. Now about the force of that recoil... That's a wee bit off. ;)

:wise:


Edit: This post was never intended as the first post in a new thread. The mods were so kind to split a thread wizz and I derailed badly with this discussion. :)
 
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<split post>
Now about the force of that recoil... That's a wee bit off. ;)

Depends... maybe the laser weapons have some mobile parts, like some kind of cooling system that moves when you fire, causing a type of recoil? :silly2:
 
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And rightly so since photons do carry a momentum. This is how solar sails work. A laser and yes, even a flashlight, have a recoil. Now about the force of that recoil... That's a wee bit off. ;)

:wise:

Well, yes and no - photons don't have mass, their momentum is more a side effect of their speed.

However, solar sails work that way, so yes, a laser emitting several 100 kilo watts of power per pulse will cause a momentum in the opposite direction - but the short duration of one pulse in combination with the inertia of the gun will completely prevent any visible effect on the gun, let alone on the one holding it.
 
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Depends... maybe the laser weapons have some mobile parts, like some kind of cooling system that moves when you fire, causing a type of recoil? :silly2:

Come on, please don't spoil it. The fact that a laser generates thrust is pretty cool (pardon the pun) in itself.

:)
 
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However, solar sails work that way, so yes, a laser emitting several 100 kilo watts of power per pulse will cause a momentum in the opposite direction - but the short duration of one pulse in combination with the inertia of the gun will completely prevent any visible effect on the gun, let alone on the one holding it.

Of course! However you said

And laser rifles have recoil in EU... :silly2:

When you should have said

And laser rifles have noticeable recoil in EU... :silly2:

:silly:

Edit: I can not agree that "their momentum is more a side effect of their speed" but lets leave that for another physics lecture. ;)

Edit 2: Also you don't need "several 100 kilo watts of power per pulse" to create thrust. A single photon will do. It's just not a lot of thrust. :)

Edit 3: Woohoo, laser derailment!

0.jpg
 
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wizzszz

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Depends... maybe the laser weapons have some mobile parts, like some kind of cooling system that moves when you fire, causing a type of recoil? :silly2:

Parts that are connected to the gun do cause a recoil when their movement begins and cause a recoil the other way when their movement stops.

If that part moves slowly, the recoil is very weak (not visible), if it moves very quickly, the END of the movement will be very shortly after the beginning and completely annihilate any visible effect by a negative recoil of the same strength.

The entire "system" (guy holding the gun) has to conserve momentum, only if something leaves the "system", we have an observable effect.
 

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Of course! However you said

When you should have said

Edit 2: Also you don't need "several 100 kilo watts of power per pulse" to create thrust. A single photon will do. It's just not a lot of thrust. :)

Yes, you are right - what an unforgiveable carelessness on a forum full of physicians... :silly2:


Momentum alone doesn't cause recoil though, you have to overcome inertia.


Edit: I can not agree that "their momentum is more a side effect of their speed" but lets leave that for another physics lecture. ;)

Momentum is defined as mass * velocity.

Photons don't have mass.



They do have a pseudo mass originating from their speed though.
 
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Yes, you are right - what an unforgiveable carelessness on a forum full of physicians... :silly2:

Stand in the corner and think about what you did! :silly2:

Momentum is defined as mass * velocity.

Photons don't have mass.

That's exactly why I didn't agree. Also the formula doesn't even apply here.

They do have a pseudo mass originating from their speed though.

That's not quite to my liking, either. I would say that photons do have mass, just no rest mass.

Also I just realized that a laser weapon with a yellow beam would have more recoil than a laser weapon with a green beam if the number of photons per pulse were equal. :laugh:
 

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Stand in the corner and think about what you did! :silly2:

Won't do it again... promised!!! *sniff*

That's exactly why I didn't agree. Also the formula doesn't even apply here.

That's the formula that is applicable here - what other formula would you suggest?
The adapted version for special relativity isn't really different.

That's not quite to my liking, either. I would say that photons do have mass, just no rest mass.

Rest mass and photons that never rest, always move... :silly2:

Yes, it has a rest mass of zero - it has a relativistic mass though (that's what i meant by "peudo-mass"), originating from it's movement, just as the relativistic momentum it has - mass is a necessary component here, no mass (relativistic or not), no momentum.


There is no english version of that wiki article on relativistic momentum...

But maybe google translate will help:

http://de.wikipedia.org/wiki/Relativistischer_Impuls

Also I just realized that a laser weapon with a yellow beam would have more recoil than a laser weapon with a green beam if the number of photons per pulse were equal. :laugh:

I disagree - green light "carries" more energy than yellow light, that much is true.

The wave propagation speed (and subsequently the relativistic mass and the relativistic momentum) is the same on both (constant speed of light).




/Edit:
I did a bit research and found out that the paragraph written above is wrong.

The momentum of photons is directly proportional to it's frequency.


So yes, green light causes more "recoil" than yellow light.
 
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[Biiiig snip!]

I think we derailed this thread enough and we should continue this when the opportunity arises to derail another one!

:silly:

One last thing, tho: I mixed up yellow and green because I looked at a spectrum chart with high frequencies on the left and low on the right while I was expecting the reverse. You're right, green light gives more recoil!

Have a great day! :D
 

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I think we derailed this thread enough and we should continue this when the opportunity arises to derail another one!

We wouldn't derail any threads now, would we? :silly2:

But yes, you are right - leaving this thread alone... for now. ;)

One last thing, tho: I mixed up yellow and green because I looked at a spectrum chart with high frequencies on the left and low on the right while I was expecting the reverse. You're right, green light gives more recoil!

I didn't even notice that you mixed them up... :D

Have a great day! :D

Thx :) Have a great day, too!
 

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Momentum is defined as mass * velocity.

Photons don't have mass.



They do have a pseudo mass originating from their speed though.

Off topic but I thought this was interesting.

Photons dont exist.

http://www.the-phoney-photon.com/

My original thought was this: Momentum is proportional to mass. An object with no mass can produce no momentum (it also doesnt exist). Einstein invented the photon in the same way that the Greeks invented the phologiston. It was a way to explain an unknown without resorting to deification of a phenomenon.

I did some research to find out if others had come up with the same thoughts, and found the URL above as one example among many.
 

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Off topic but I thought this was interesting.

Photons dont exist.

http://www.the-phoney-photon.com/

My original thought was this: Momentum is proportional to mass. An object with no mass can produce no momentum (it also doesnt exist). Einstein invented the photon in the same way that the Greeks invented the phologiston. It was a way to explain an unknown without resorting to deification of a phenomenon.

I did some research to find out if others had come up with the same thoughts, and found the URL above as one example among many.

I'd really love to give you a lengthy explanation and several reasons why this is not true imho.

But we've hijacked this thread long enough...



Dear mods,
you are soooo quick when i post a "bullshit" and delete that within minutes - but when a thread needs to be split up, there is no trace of you...

I'll report this post and request a split, maybe you do the same.
 

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Off topic but I thought this was interesting.

Photons dont exist.

http://www.the-phoney-photon.com/

My original thought was this: Momentum is proportional to mass. An object with no mass can produce no momentum (it also doesnt exist). Einstein invented the photon in the same way that the Greeks invented the phologiston. It was a way to explain an unknown without resorting to deification of a phenomenon.

I did some research to find out if others had come up with the same thoughts, and found the URL above as one example among many.

"The phoney photon" is an interesting read. I guess i fall into the category of people he mentions whose response is "the concept works". A rose by any other name would still cause the PE. :laugh: And I'm not working on anything that requires an exotic property of photons.

Regarding the momentum of light, off the top of my head i don't know that there's any other suitable explanation for the solar wind, but i'm not an astrophysicist.

<split post>
 
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I'd really love to give you a lengthy explanation and several reasons why this is not true imho.

But we've hijacked this thread long enough...



Dear mods,
you are soooo quick when i post a "bullshit" and delete that within minutes - but when a thread needs to be split up, there is no trace of you...

I'll report this post and request a split, maybe you do the same.

Agreed this is a fun topic. Split it. :)

The only particles without mass so far are (2) particles, a graviton and a photon. The doubt of the graviton even existing is well recognized in science. Gluons are also potentially zero mass, however a single gluon cannot exist in nature, these are created en masse (no pun intended) as a result of instances of high energy between other particles. Neutrinos have mass, all of them, so these are counted out at this stage in the game.

So really we have only 1 recognized massless particle, the photon, which we are to believe exists because of some sort of magical loophole in the laws of physics? Meh, I'm not a fan of exceptions to rules. It usually means the rule is broken (at least misunderstood by us), or the subject of study within that rule is not what it is understood to be.

My thought is that a photon, as well as a graviton, is much the same as a gluon. It's a name given to a high energy phenomenon which occurs, but which does not actually exist in its own independent state.
 

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Please, let's wait for the mods to split this thread - or, if you don't want to wait, open a new thread.
 

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Dear mods,
you are soooo quick when i post a "bullshit" and delete that within minutes - but when a thread needs to be split up, there is no trace of you...

I'll report this post and request a split, maybe you do the same.

I guess the others left this for me to do, for experience... and it was 3am for me when you requested this. :zzz:

Original thread split and relevant posts moved - including splitting posts where required to retain integrity of both threads.
 

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Are you guys telling me there is no little green man inside my laser rifle who throws lasers? :eyecrazy: I'm shocked!


Guess no theories are safe anymore ;)



Makes me wonder, what if a comment derails a derailed thread? is there then no hope for humanity :D
 

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I guess the others left this for me to do, for experience... and it was 3am for me when you requested this. :zzz:

Original thread split and relevant posts moved - including splitting posts where required to retain integrity of both threads.

First of all a thank you, Serica - it's the first time that a split request i made actually succeded.

Maybe the other mods don't know how to do it? :silly2:


Then:

Off topic but I thought this was interesting.

Photons dont exist.

http://www.the-phoney-photon.com/

My original thought was this: Momentum is proportional to mass. An object with no mass can produce no momentum (it also doesnt exist). Einstein invented the photon in the same way that the Greeks invented the phologiston. It was a way to explain an unknown without resorting to deification of a phenomenon.

I did some research to find out if others had come up with the same thoughts, and found the URL above as one example among many.

Photons do exist - everyone who ever had a sunburn can tell you this... :silly2:

We can generate them, we can count (!) them, yes, we can even trap them!

They have no REST mass, but they have a relativistic mass, originating from their speed (you know that things get heavier when accelerated - the effect is very small in everyday physics, but if you get closer to the speed of light, the effect become eventually very large)


And the naming is whole 'nother story - if i create an object, something a human can sit on, and call it "foo", and later on we find out that what i actually meant was a "chair" - does the object cease to exist?

No, you only chose to give it a different name. Doer has pointed that out in his post already.
(and maybe watch the trainman scene from Matrix II, there is a similar discussion about what humans call "love")


It is counterintuitive that something with no mass appears to have momentum, but if you see a photon as pure energy - and then apply einsteins famous formula (e=m*c²) you will see that there is no real difference between matter (which has mass) and energy (a light quantum in our case).


And maybe let me pick up the example with ancient greeks to illustrate this further:
Their concept of "phlogiston" is now known was incorrect, yet the observed effect is still there and very real.

If you see it from a different angle, and see "phlogiston" as the "volatile matter" (the gases and matter that turns from solid into gas due to oxidation and heat) that escapes from a burning object, we have just added a more distinct, a more exact definition to their concept, but we haven't disproven it - burning objects still do lose weight.


If you chose to describe the effect (or the lost matter) with the term "foobar" doesn't really change anything.


And last but not least, that photons do have momentum is proven beyond any reasonable doubt - not only solar sails or gravitational lenses show that, but we can observe the momentum of photons with simply toys as "solar spinners"



I found no article to explain what solar spinners are, but maybe the a pic will help:

solar_sp5.jpg


It's basically an evacuated glass orb with a windmill-like wheel inside, the paddels are painted black on one side, white (or silver) on the other... basically a very tiny solar sail.

The dark side absorbs the light, the bright side reflects it. Enough to get this toy spinning.

Another pic:

stock-photo-solar-spinner-with-white-background-and-blue-lighted-base-33174856.jpg
 
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And last but not least, that photons do have momentum is proven beyond any reasonable doubt - not only solar sails or gravitational lenses show that, but we can observe the momentum of photons with simply toys as "solar spinners"



I found no article to explain what solar spinners are, but maybe the a pic will help:

solar_sp5.jpg


It's basically an evacuated glass orb with a windmill-like wheel inside, the paddels are painted black on one side, white (or silver) on the other... basically a very tiny solar sail.

The dark side absorbs the light, the bright side reflects it. Enough to get this toy spinning.

Another pic:

stock-photo-solar-spinner-with-white-background-and-blue-lighted-base-33174856.jpg

Sorry to tinkle on your parade once more, wizz, but light mills (or solar spinners) do not move by the momentum difference of absorbed and reflected photons. They move because of the heat difference of the two sides of their blades and the effect that has on the remaining gas molecules in the cylinder. They do NOT work if the vacuum is more or less total.

:ahh:
 

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My last post may have been a bit ambiguous. Let me put it another way: AFAIK the arguments made in Phoney Photons (PP) successfully rebut the known justifications for positing a "photon". I recognize the utility of a "photon" as a useful concept, but as for its actual existence, my own rusty QM and other physics knowledge fail to generate a counter argument to PP. Does anyone else know of an observation or experiment that supports the existence of photons beyond the three pillars that are mentioned and undermined in PP?

I had mentioned the solar wind, but as was pointed out in a PM, the momentum imparted by the solar wind could be due to energetic particles rather than EM (and the two must be distinguished in the absence of "photons" and hence wave-particle duality).
 

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Sorry to tinkle on your parade once more, wizz, but light mills (or solar spinners) do not move by the momentum difference of absorbed and reflected photons. They move because of the heat difference of the two sides of their blades and the effect that has on the remaining gas molecules in the cylinder. They do NOT work if the vacuum is more or less total.

:ahh:

You really hate me, don't you? :silly2:



But now, having a better english term for it, i found a link:

Crookes radiometer

Click the link and check #1 - Crooke himself explained the movement with the Radiation pressure, basically what i outlined above - it's been a while since i read about it (20 years easily), and all i remember was the explanation given above... *sigh*

A damn cool toy nonetheless... however, that light quantums have momentum, even more with higher frequency (higher energy), is still correct.
 

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My last post may have been a bit ambiguous. Let me put it another way: AFAIK the arguments made in Phoney Photons (PP) successfully rebut the known justifications for positing a "photon". I recognize the utility of a "photon" as a useful concept, but as for its actual existence, my own rusty QM and other physics knowledge fail to generate a counter argument to PP. Does anyone else know of an observation or experiment that supports the existence of photons beyond the three pillars that are mentioned and undermined in PP?

I had mentioned the solar wind, but as was pointed out in a PM, the momentum imparted by the solar wind could be due to energetic particles rather than EM (and the two must be distinguished in the absence of "photons" and hence wave-particle duality).

The case of the Nichols radiometer experiment mentioned does make a pretty compelling argument that light exerts pressure. I wonder if PP's writer has considered that.
 

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My last post may have been a bit ambiguous. Let me put it another way: AFAIK the arguments made in Phoney Photons (PP) successfully rebut the known justifications for positing a "photon". I recognize the utility of a "photon" as a useful concept, but as for its actual existence, my own rusty QM and other physics knowledge fail to generate a counter argument to PP. Does anyone else know of an observation or experiment that supports the existence of photons beyond the three pillars that are mentioned and undermined in PP?

A photon carries a measureable, distinct "quantum" of energy (hence "light quantum" - i fail to see how a wave can produce such results.

And, the photoelectric effect (for which Einstein received the nobel prize), clearly shows that there is an amount X of energy per photon minus the Work function leaves a remainder of Y for a specific wave length for a single photon.

No idea how you would explain these discrete observations with an amorphous "wave" only.

Btw - the wave/particle duality is only required when you follow the Copenhagen interpretation - i, for one, believe in the De Broglie–Bohm theory which gets along without the "wave" part just fine.

So, if anything, photons are particles rather than waves.



I had mentioned the solar wind, but as was pointed out in a PM, the momentum imparted by the solar wind could be due to energetic particles rather than EM (and the two must be distinguished in the absence of "photons" and hence wave-particle duality).

Energetic particles coming from the sun (or any other star)??
Because, direction matters a lot here...


And btw - photons are not "energetic particles"?


The case of the Nichols radiometer experiment mentioned does make a pretty compelling argument that light exerts pressure. I wonder if PP's writer has considered that.

Nice find, +rep! :)

Maybe i fell for this:

This apparatus is sometimes confused with the Crookes radiometer of 1873, in which vanes turn in a partial vacuum under the influence of low pressure gas molecules and not directly by the photons themselves.

Eat this, Audrey!!! ;)
 
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You really hate me, don't you? :silly2:

Awww, come here, you! :hug:

But now, having a better english term for it, i found a link:

Crookes radiometer

Click the link and check #1 - Crooke himself explained the movement with the Radiation pressure, basically what i outlined above - it's been a while since i read about it (20 years easily), and all i remember was the explanation given above... *sigh*

Dude, read your link, this is what is says:

"1.Crookes incorrectly suggested that the force was due to the pressure of light."

A damn cool toy nonetheless... however, that light quantums have momentum, even more with higher frequency (higher energy), is still correct.

I gave my mom one of these for Christmas 2010 if I remember correctly. :) (I broke her original one when I was a child over 30 years ago, tho. :ahh:)
 

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A photon carries a measureable, distinct "quantum" of energy (hence "light quantum" - i fail to see how a wave can produce such results.

And, the photoelectric effect (for which Einstein received the nobel prize), clearly shows that there is an amount X of energy per photon minus the Work function leaves a remainder of Y for a specific wave length for a single photon.

No idea how you would explain these discrete observations with an amorphous "wave" only.

I would cite Phoney Photons. :silly2: As i said, he makes a pretty good argument that light only is quantized when it is converted to other energies, and that's only because it interacts with (quantized) matter. If you're not going to at least glance at the assigned reading, it's hard to have a discussion about it... :p

I would expect that light having momentum would be one of the evidences of it being a particle. Perhaps i'll email the writer about it and see what his take is.
 

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Dude, read your link, this is what is says:

"1.Crookes incorrectly suggested that the force was due to the pressure of light."

Yes, "incorrectly", i know - i think i made it clear that i, incorrectly, too, followed his original explanation.

I linked it as an explanation on why i went wrong and that it happened to the inventor, too - not as an objection.



However, i'm no longer sure if i didn't mix them up (read my last post)... :tongue2:

I would cite Phoney Photons. :silly2: As i said, he makes a pretty good argument that light only is quantized when it is converted to other energies, and that's only because it interacts with (quantized) matter. If you're not going to at least glance at the assigned reading, it's hard to have a discussion about it... :p

I am about to read it (sorry, english is not my first language, and all the english tech terms... let's just say it takes a bit...)

I am, however, on the complete opposite side here (please read De Broglie–Bohm theory), which doesn't even need the wave part...

This quote (from "the phoney photon"):
I focused all my efforts down to removing its necessity

is pretty much what De Broglie did, too - just that he removed the necessity for the WAVE part.


I would expect that light having momentum would be one of the evidences of it being a particle. Perhaps i'll email the writer about it and see what his take is.

He will probably say it is an effect of said "quantization"...
 
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Yes, "incorrectly", i know - i think i made it clear that i, incorrectly, too, followed his original explanation.

I linked it as an explanation on why i went wrong and that it happened to the inventor, too - not as an objection.



However, i'm no longer sure if i didn't mix them up (read my last post)... :tongue2:

I am so confused. Anyway, if you agree that light mills don't work because of light pressure then I am happy!

:yay:

About what pushes solar sails, EM radiation or charged particles:

"Solar wind, the flux of charged particles blown out from the sun, exerts a nominal dynamic pressure of about 3 to 4 nPa, three orders of magnitude less than solar radiation pressure on a reflective sail."

http://en.wikipedia.org/wiki/Solar_sail#Solar_radiation_pressure
 

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Meanwhile back in the EU reality, I am not convinced those laser rifles are actually shooting photons at all. Have you noticed the ridiculously low speed of the beam? How can one slow down photons to that degree? Perhaps they are actually tightly focussed plasma? Weapon recoil would make a lot more sense in that context. Would also be consistant with the observed transfer of momentum to the target.
 

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Meanwhile back in the EU reality, I am not convinced those laser rifles are actually shooting photons at all. Have you noticed the ridiculously low speed of the beam? How can one slow down photons to that degree? Perhaps they are actually tightly focussed plasma? Weapon recoil would make a lot more sense in that context. Would also be consistant with the observed transfer of momentum to the target.

Obviously your LWT skill is too low. :lolup:

The answer is simple. The "atmosphere" of calypso is a Bose-Einstein condensate. :laugh:

About what pushes solar sails, EM radiation or charged particles:

"Solar wind, the flux of charged particles blown out from the sun, exerts a nominal dynamic pressure of about 3 to 4 nPa, three orders of magnitude less than solar radiation pressure on a reflective sail."

http://en.wikipedia.org/wiki/Solar_sail#Solar_radiation_pressure

Yeah, once i was reminded that there are experiments showing light does exert pressure (even in a vacuum), the solar wind argument was moot.
 
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