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Posted: 12/29/2009 5:15:12 PM EDT
[#1]
well then someone explain how a solar sail works then
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Posted: 12/29/2009 5:15:36 PM EDT
[#2]
Just thought I'd drop in and watch this one.
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Posted: 12/29/2009 5:16:07 PM EDT
[#3]
Quoted: well then someone explain how a solar sail works then Light does have momentum. |
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Posted: 12/29/2009 5:19:01 PM EDT
[#4]
Quoted:
The mass of a photon is relativistic. It has no mass when not moving because it is pure energy, according to Einstein's famous e=mC^2 Get a radiometer and then draw the free body diagram of the torque, noting the reflective and absorptive vanes, using conservation of momentum. If it had no mass when not moving, it would have zero energy, not be pure energy. 0=0*0. So, while you are right about it having no mass the deduction about pure energy doesn't follow from e=mC^2. |
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Posted: 12/29/2009 5:24:33 PM EDT
[#5]
Quoted:
Quoted:
The mass of a photon is relativistic. It has no mass when not moving because it is pure energy, according to Einstein's famous e=mC^2 Get a radiometer and then draw the free body diagram of the torque, noting the reflective and absorptive vanes, using conservation of momentum. If it had no mass when not moving, it would have zero energy, not be pure energy. 0=0*0. So, while you are right about it having no mass the deduction about pure energy doesn't follow from e=mC^2. The typical E = mc^2 that everyone knows and loves is given as relativistic mass, not rest mass. Once expanded, it becomes E^2 = (p^2)(c^2) + (m_0^2)(c^4), where in this case, m_0 is rest mass and p is momentum. So, while a photon has no rest mass, it does indeed have momentum, meaning it has energy. |
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Posted: 12/29/2009 5:24:59 PM EDT
[#6]
Quoted: I shined my flashlight on my scale but the dial didn't move.  so, can you accidentally,,, the whole thing, of photon? |
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Posted: 12/29/2009 5:28:42 PM EDT
[#7]
Wait, is the photon on a treadmill?
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Posted: 12/29/2009 5:31:49 PM EDT
[#8]
Isaac Asimov's Book of Facts:
"If a set of fine scales is arranged so that one scale is kept dark, and light is allowed to fall on the other, the lighted scale will sink slowly. Light has "weight." The pressure of light on the Earth's surface is calculated as two pounds per square mile." |
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Posted: 12/29/2009 5:37:48 PM EDT
[#9]
Quoted:
Isaac Asimov's Book of Facts: "If a set of fine scales is arranged so that one scale is kept dark, and light is allowed to fall on the other, the lighted scale will sink slowly. Light has "weight." The pressure of light on the Earth's surface is calculated as two pounds per square mile." Not weight in the sense we normally think of, i.e. F=m*a. A dark scale will absorb light, whereas a light scale will reflect it. This will vary the change in momentum experienced by each scale, creating different impulses, and registering as different forces (weights). That is the principle behind the little flag-in-a-bulb things mentioned before, but it has nothing to do with what we associated with the acceleration of gravity acting on a mass that we normally associated with weight. |
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Posted: 12/29/2009 5:39:58 PM EDT
[#10]
Ok, here's a brain twister.
Those of you mentioning that gravity does not affect photons, but instead the 'space' around it. If we assume space to be a perfect vacuum (the absence of anything, except for these purposes, some photons zipping by), then how does gravity effect any change to 'it'?  |
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Posted: 12/29/2009 5:40:23 PM EDT
[#11]
Quoted:
weigh yourself. then, hold a photon and weigh yourself again. subtract Good idea. Just don't do it while holding a helium balloon.. I gotta go. This threads gonna mess with my head. 
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Posted: 12/29/2009 5:41:10 PM EDT
[#12]
Quoted:
Photons from a Fenix TK11 have twice as much mass as natural light, and it can knock over styrofoam cups from 6 feet away. LOL! |
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Posted: 12/29/2009 5:43:03 PM EDT
[#13]
Depends... lekos, cans or fresnels?
I usually throw a brick on the arbor for every 3 or 4 and check for trim. |
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Posted: 12/29/2009 5:45:15 PM EDT
[#14]
because your perspective is the one that matters.
Quoted: so if photons are going away from you at the speed of light, aren't you going away from the photons at the speed of light from their perspective? If so, how come I can go the speed of light and not have to use infinite energy? |
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Posted: 12/29/2009 5:45:56 PM EDT
[#15]
Threads like these make my head hurt.
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Posted: 12/29/2009 5:46:08 PM EDT
[#16]
they have some or else solar sails wouldn't work.
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Posted: 12/29/2009 5:47:25 PM EDT
[#17]
Quoted:
Ok, here's a brain twister. Those of you mentioning that gravity does not affect photons, but instead the 'space' around it. If we assume space to be a perfect vacuum (the absence of anything, except for these purposes, some photons zipping by), then how does gravity effect any change to 'it'? Gravity would have no effect on light in a pure vacuum. When gravity bends light, it's due to the mass of an object "near" the light. |
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Posted: 12/29/2009 5:50:14 PM EDT
[#18]
Light does not have mass, but it does have momentum so it can "push" on stuff.
I am not sure why it is important, or, why ya'll think that noodling it out will work when the same thing (photons) is both a wave (when you aren't looking) and is a particle (when you are) at the same time. Sometimes ya gotta just go "well, my Wii still works so I don't give a shit." |
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Posted: 12/29/2009 5:50:40 PM EDT
[#19]
let's say you are in a box on a platform that shakes so you can't tell if you are moving or not. attached to the box is a radar gun and you can see the display but you cannot see out of the box.
The radar is pointed at the car. One of you is moving away from the other at 70mph
How will the display read if you are stationary and the car is moving? what about if you are moving and the car is stationary? What makes your question relevant, is that you and the car have a common frame of reference, namely the ground (or road, etc). But what if you are in space and the only point of reference is each other? You could both be traveling at 35mph and to each other the other one would appear to be traveling away at 70mph. Quoted: Quoted: so if photons are going away from you at the speed of light, aren't you going away from the photons at the speed of light from their perspective? If so, how come I can go the speed of light and not have to use infinite energy? If someone drives a car at 70 mph away from you, are you travelling 70 mph away from them? Or are you standing still? |
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Posted: 12/29/2009 5:50:54 PM EDT
[#20]
Quoted: Threads like these make my head hurt. Suck it up, it's good pain!  |
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Posted: 12/29/2009 5:52:03 PM EDT
[#21]
Quoted: Light does not have mass, but it does have momentum so it can "push" on stuff. I am not sure why it is important, or, why ya'll think that noodling it out will work when the same thing (photons) is both a wave (when you aren't looking) and is a particle (when you are) at the same time. Sometimes ya gotta just go "well, my Wii still works so I don't give a shit." I don't know, maybe some of us have fun thinking about this stuff?  |
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Posted: 12/29/2009 5:52:22 PM EDT
[#22]
Slightly less than an Aircraft on a treadmill taking off
  
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Posted: 12/29/2009 5:55:02 PM EDT
[#23]
Quoted: Quoted: Gravity would have no effect on light in a pure vacuum. Ok, here's a brain twister. Those of you mentioning that gravity does not affect photons, but instead the 'space' around it. If we assume space to be a perfect vacuum (the absence of anything, except for these purposes, some photons zipping by), then how does gravity effect any change to 'it'? When gravity bends light, it's due to the mass of an object "near" the light. I think you might be on the right track but you said that very badly. Mass (of other things) is needed to bend space. Light then travels in a "straight line" through this bent space. The light therefore appears to bend. The straight line path that the light follows would also appear to be an actual straight line if there were no nearby massive bodies. |
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Posted: 12/29/2009 5:58:07 PM EDT
[#24]
Quoted: Quoted: Ok, here's a brain twister. Those of you mentioning that gravity does not affect photons, but instead the 'space' around it. If we assume space to be a perfect vacuum (the absence of anything, except for these purposes, some photons zipping by), then how does gravity effect any change to 'it'? Gravity would have no effect on light in a pure vacuum. When gravity bends light, it's due to the mass of an object "near" the light. If gravity has zero effect on photons (this is current accepted theory, I understand), then I wonder why other things do. Gravity can affect a medium, and a medium can affect photons. But gravity cannot affect photons in any way without aid from a medium? I wonder to what extent this has been proven, and under what conditions. Because I am having a difficult time imagining an accurately reproducible experiment (mathematical or otherwise) that could establish this without relying someone heavily on other theories. |
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Posted: 12/29/2009 6:03:03 PM EDT
[#25]
Quoted: If gravity has zero effect on photons (this is current accepted theory, I understand), then I wonder why other things do. Gravity can affect a medium, and a medium can affect photons. But gravity cannot affect photons in any way without aid from a medium? I wonder to what extent this has been proven, and under what conditions. Because I am having a difficult time imagining an accurately reproducible experiment (mathematical or otherwise) that could establish this without relying someone heavily on other theories. No! There is no "medium" in space. Gravity effects the space itself. This has an apparent effect on things in that space including light and objects of mass. |
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Posted: 12/29/2009 6:04:32 PM EDT
[#26]
Quoted:
Quoted:
Quoted:
Gravity would have no effect on light in a pure vacuum.
Ok, here's a brain twister. Those of you mentioning that gravity does not affect photons, but instead the 'space' around it. If we assume space to be a perfect vacuum (the absence of anything, except for these purposes, some photons zipping by), then how does gravity effect any change to 'it'? When gravity bends light, it's due to the mass of an object "near" the light. I think you might be on the right track but you said that very badly. Mass (of other things) is needed to bend space. Light then travels in a "straight line" through this bent space. The light therefore appears to bend. The straight line path that the light follows would also appear to be an actual straight line if there were no nearby massive bodies. You're right, I did say that badly. In my head the two comments directly follow each other, but yeah, you need the comment regarding space being the medium. I'll stop now
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Posted: 12/29/2009 6:08:33 PM EDT
[#27]
It's been a long while since college...
Isn't the whole "bends space" thing more of a model of the behavior than an explanation? Has space been defined to the point where we can quantify it? sort of like the "gravity well" of a black hole. It's a great model and we can do math around the event horizon and all that, but we really haven't been able to define gravity beyond a few constants and distance / mass relationships. Or am I really that far out of touch on my physics? Quoted: Quoted: If gravity has zero effect on photons (this is current accepted theory, I understand), then I wonder why other things do. Gravity can affect a medium, and a medium can affect photons. But gravity cannot affect photons in any way without aid from a medium? I wonder to what extent this has been proven, and under what conditions. Because I am having a difficult time imagining an accurately reproducible experiment (mathematical or otherwise) that could establish this without relying someone heavily on other theories. No! There is no "medium" in space. Gravity effects the space itself. This has an apparent effect on things in that space including light and objects of mass. |
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Posted: 12/29/2009 6:14:24 PM EDT
[#28]
Quoted: It's been a long while since college... Isn't the whole "bends space" thing more of a model of the behavior than an explanation? Has space been defined to the point where we can quantify it? sort of like the "gravity well" of a black hole. It's a great model and we can do math around the event horizon and all that, but we really haven't been able to define gravity beyond a few constants and distance / mass relationships. Or am I really that far out of touch on my physics? You are pretty much right. This is still a very "new" area of physics with much theorizing and debate going on. I was simply giving an explanation based on the accepted model without attempting to give an explanation as to "why". There is a reason for that. I do not know the "why" and I don't know many people who think they do either. |
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Posted: 12/29/2009 6:18:57 PM EDT
[#29]
Quoted:
but light can be bent by gravity. it has to have mass if gravity can effect it, right? Yes, but most of the people who have less intelligence than education seem to think otherwise. There are two main flaws in physics. One is the assumption that light ALWAYS travels at a constant speed, the other is that time can speed-up or slow down. Prove me wrong.
Quoted:
so if photons are going away from you at the speed of light, aren't you going away from the photons at the speed of light from their perspective? If so, how come I can go the speed of light and not have to use infinite energy? From their perspective, yes. ...but you're standing still for all intents and purposes. |
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Posted: 12/29/2009 6:22:57 PM EDT
[#30]
Quoted: Quoted: If gravity has zero effect on photons (this is current accepted theory, I understand), then I wonder why other things do. Gravity can affect a medium, and a medium can affect photons. But gravity cannot affect photons in any way without aid from a medium? I wonder to what extent this has been proven, and under what conditions. Because I am having a difficult time imagining an accurately reproducible experiment (mathematical or otherwise) that could establish this without relying someone heavily on other theories. No! There is no "medium" in space. Gravity effects the space itself. This has an apparent effect on things in that space including light and objects of mass. Agreed. Or at least, there is so little substance (Gas, particulates, etc: Medium) that it could not possible explain the effects observed on photons by high gravitational anomalies. So, if gravity cannot affect photons without a medium, but extremely powerful gravitational anomalies seem to have an effect on photons anyways, then Space must be the medium. How do we quantify the 'fabric' of Space if it is a perfect vacuum? Would it be reasonable to assume this fabric is in fact the gravitational effects of bodies with measurable mass, and the interactions of the gravitational effects? (This was where I was originally trying to clumsily steer things, and it's one I enjoy pondering). |
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Posted: 12/29/2009 6:28:17 PM EDT
[#31]
The notion of a photon as a discrete light particle is a MODEL, and the model has bandwidth. It's functional for making predictions in certain scenarios and it has engineering merit, but it is backwards to use a limited-function model to shape your analysis of the actual physicality.
The simple answer to the 'dualities' and oddities is that the model is incorrect or incomplete. |
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Posted: 12/29/2009 6:30:09 PM EDT
[#32]
Quoted:
Quoted:
African, or European? What? I don't know that! AAAAAAAAaaaaaaaaaaaaaaaahhhhhhhh!!!!!!!!!1 Stupid bridge! What is the velocity of an unlaiden swallow? 
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Posted: 12/29/2009 6:31:21 PM EDT
[#33]
Light (unlike all other waveform phenomena) does not need a medium to propagate.
It is it's own medium for all intents and purposes. See the illustrated version for details.  |
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Posted: 12/29/2009 6:48:41 PM EDT
[#34]
Quoted:
So, if gravity cannot affect photons without a medium, but extremely powerful gravitational anomalies seem to have an effect on photons anyways, then Space must be the medium. How do we quantify the 'fabric' of Space if it is a perfect vacuum? Would it be reasonable to assume this fabric is in fact the gravitational effects of bodies with measurable mass, and the interactions of the gravitational effects? (This was where I was originally trying to clumsily steer things, and it's one I enjoy pondering). Fabric-of-space, ether/medium concepts, dark matter, and dark energy are all weak extrapolations that people make up (and don't test) to explain away the deficiencies of their model. |
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Posted: 12/29/2009 6:54:25 PM EDT
[#35]
Quoted:
Dark is Heavy though! There is no such thing as "Dark" it is just the absence of Light. And light does have Mass as far as I remember. It is very light however. |
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Posted: 12/29/2009 7:01:38 PM EDT
[#36]
Quoted: Being that I do not have any model, and I am implying in my quote that 'fabric of Space' and Space are concepts that we gave name to to describe the effects of gravitational fields on other things, I'm not sure what you're implying?Quoted: So, if gravity cannot affect photons without a medium, but extremely powerful gravitational anomalies seem to have an effect on photons anyways, then Space must be the medium. How do we quantify the 'fabric' of Space if it is a perfect vacuum? Would it be reasonable to assume this fabric is in fact the gravitational effects of bodies with measurable mass, and the interactions of the gravitational effects? (This was where I was originally trying to clumsily steer things, and it's one I enjoy pondering). Fabric-of-space, ether/medium concepts, dark matter, and dark energy are all weak extrapolations that people make up (and don't test) to explain away the deficiencies of their model. |
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Posted: 12/29/2009 7:05:14 PM EDT
[#37]
Quoted: they have some or else solar sails wouldn't work. Are we talking light photons or other forms of "charged particles" which defnately do have mass? |
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Posted: 12/29/2009 7:08:13 PM EDT
[#38]
This is very important to me, but it's late and I'm tired, so I'm going to bed, but will wake up bright and early for the all-important answer. Just don't know how I could start my day without it.
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Posted: 12/29/2009 7:09:09 PM EDT
[#39]
Quoted:
Quoted:
The weight of light depends on whether its a particle or a wave. In typical arfcom fashion, its both!
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Posted: 12/29/2009 7:11:33 PM EDT
[#40]
Quoted: Quoted: Are we talking light photons or other forms of "charged particles" which definitely do have mass?they have some or else solar sails wouldn't work. Solar sails are propelled using pressure from light. Photons do have momentum. |
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Posted: 12/29/2009 7:11:51 PM EDT
[#41]
Quoted: Quoted: Quoted: In typical arfcom fashion, its both!The weight of light depends on whether its a particle or a wave.  |
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Posted: 12/29/2009 7:14:31 PM EDT
[#42]
The morning after a night of heavy alcohol cosumption when you open the blinds, light is pretty damn heavy.
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Posted: 12/30/2009 5:43:44 AM EDT
[#43]
Quoted:
Quoted:
well then someone explain how a solar sail works then Light does have momentum. how does something with out mass have momentum??? 
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Posted: 12/30/2009 5:46:19 AM EDT
[#44]
Quoted:
weigh yourself. then, hold a photon and weigh yourself again. subtract You've blinded me with science. |
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Posted: 12/30/2009 6:14:28 AM EDT
[#45]
Quoted: how does something with out mass have momentum??? E = energy p = momentum c = speed of light in a vacuum m = rest mass h = Planck constant v = frequency In relativistic mechanics, this is one way to define the energy of a particle. E2 = (pc)2 + (mc2)2 Since light has no rest mass the second term drops out of the equation. E2 = (pc)2 Simplifying... E = pc From my avatar. E = hv Combine equations. hv = pc Momentum of a photon is a function of its frequency.  p = (hv)/c |
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Posted: 12/30/2009 12:27:12 PM EDT
[#46]
No comments?
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Posted: 12/30/2009 12:35:46 PM EDT
[#47]
...
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Posted: 12/30/2009 12:38:07 PM EDT
[#48]
87 units.
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Posted: 12/30/2009 12:39:56 PM EDT
[#49]
Quoted:
Quoted:
but light can be bent by gravity. it has to have mass if gravity can effect it, right? No, gravity bends the fabric of space itself. Light merely travels through the curves gravity creates. What does the fabric of space consist of? |
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Posted: 12/30/2009 12:44:44 PM EDT
[#50]
Quoted: What does the fabric of space consist of? Interesting question. If you figure it out, let me know first. |
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