Talk:Radiation pressure

message: I have a problem with the statement that the energy density for a black body
is \sigma T^4/3 c. It should be 4 \sigma T^4/c which is
the radiation constant
The energy density of a black body per unit frequency is (see Planck's law of black body radiation or Hyperphysics)
:u_\nu=\frac{8\pi h}{c^3}\,\frac{\nu^3}{e^{h\nu/kt}-1}
Integrating this from ν=0 to infinity gives for the energy density
:u=\frac{8k^4\pi^5}{15c^3h^3}\,T^4
and the Stefan Boltzmann constant is (see Stefan-Boltzmann law and Stefan-Boltzmann constant)
:\sigma=\frac{2\pi^5k^4}{15c^2h^3}\,T^4
substituting gives u=4 \sigma T^4/c. Did I go wrong here or is the article wrong? PAR 00:17, 20 November 2006 (UTC)
replies: text: The compression section now has the correct value, same as above. SpaceSailor (talk) 02:50, 10 August 2013 (UTC)
thread_title:  Energy density incorrect? 

message: Neat image. Would be cool to get permission for the image somehow. --Eean 15:04, 29 March 2007 (UTC)
replies: text: The effect is from heat transfer, not light pressure.--SpaceSailor 17:13, 10 August 2013 (UTC)
thread_title:  Pressure of Light Can Move Liquid 

message: What is the total amount of light pressure of the Sun light on Earth?  —Preceding unsigned comment added by 86.163.165.101 (talk) 12:20, 27 August 2008 (UTC)
replies: text: Approximately 4.7*10^-6 Pascal.  —Preceding unsigned comment added by 86.92.80.224 (talk) 19:23, 11 June 2009 (UTC)
replies: text: Anyone else can confirm this? As atmosphere pressure is only double this at ~ 9.8×10−6  —Preceding unsigned comment added by Seb-Gibbs (talk • contribs) 19:27, 2 August 2009 (UTC)
replies: text: As the article states, the pressure at the earth is 4.6*10^-6 Pascal. That does not depend on the size of the object (i.e. the Earth). What you probably want is the force, which you get by multiplying the pressure with the cross section of the Earth. That yields a total force of Pi * (6,371 km)^2 * 4.6*10^-6 Pa = 587,000,000 newtons (i.e. the pressure from a 60 kiloton weight on the surface). Not that impressive when applied to a planet :-)Oh, and the pressure of the atmosphere at the surface is around 10^5 Pa, ie. 2*10^10 larger. At height ofcourse the atmospheric pressure drops to zero (and as it does, I guess the solar radiation is partly responsible for some of it escaping. Which is why we have almost no free hydrogen and helium in the atmosphere) Tøpholm (talk) 01:44, 5 August 2009 (UTC)
replies: text: it states that, if the whole light from the sun is absorbed, the pressure is 4.6*10^-6 Pascal. It doesn't say at any point that the earth absorbs all light, it's just a supposition in case it absorbs it all. Does any one know the real pressure? It should be between 4.6*10^-6 (fully absorbed) and  9.15*10^-6 (fully reflected) Pascal.  — Preceding unsigned comment added by 79.147.28.155 (talk) 18:18, 2 January 2012 (UTC)
thread_title:  Pressure of the Sun's light on Earth 

message: Useful for active ablative armor systems, feedback loops offer protection from bullets to explosions, as well rebreather filters can utilize this force given a sufficient power source. However verifiable sources of applied consumer goods as well as concepts are to be calculated and debated. Aditya.m4 (talk) 03:16, 19 January 2010 (UTC)
thread_title:  Radiation Pressure in Defense Systems 

message: hey i got a web http://www.blazelabs.com/f-g-rpress.asp that explain it quiet well for elementary level  —Preceding unsigned comment added by ArielGenesis (talk • contribs) 21:52, 9 June 2010 (UTC)
thread_title:  elementary explaination 

message: "It may be shown by electromagnetic theory" is insufficient theoretical reference. Please, add more detailed explanations or derivations, or apropriate references. Especially useful will be direct derivation from Maxwell equations or Lorentz force equation. Softvision (talk) 10:30, 22 January 2011 (UTC)
replies: text: Derivations from those equations would be out of scope for this article.  See those respective articles.  I am working on improving the explanations, which are definitely in need of reworking. SpaceSailor 02:48, 2 August 2013 (UTC)

text: The "theory" section has been reworked, which should take care of the concerns.  Emission pressure is now included (Previously missing).--SpaceSailor 00:30, 11 August 2013 (UTC)
thread_title:  Section Theory is insufficient 

message: This article doesn't have any explanation of WHY radiation exerts pressure. How about something that explains this in a sort of intuitive way, or if that is impossible, says that no one understands why it happens, but there is experimental proof that it does.   Right now the article is very technical, pitched towards people who have degrees in physics rather than the average reader.  It seems to assume that anyone reading it already has a basic understanding of what light pressure is and how it works.   Which is what I was trying to find out when I looked it up.     Can't you put in a top level section that is easy enough for most people to understand?   Right now you are losing about 99% of the population.  —Preceding unsigned comment added by 74.38.247.10 (talk) 13:50, 21 May 2011 (UTC)
replies: text: The revised text uses momentum to explain the existence of pressure, hopefully making it more understandable. SpaceSailor 02:54, 10 August 2013 (UTC)
thread_title:  no explanation of WHY --- and way too hard 

message: The article says "It may be shown by electromagnetic theory, by quantum theory, or by thermodynamics, making no assumptions as to the nature of the radiation, that the pressure against a surface exposed in a space traversed by radiation uniformly in all directions is equal to one third of the total radiant energy per unit volume within that space.[citation needed]". Is it really possible to derive it from thermodynamics alone, without any information about electromagnetic theory?  I would be very interested to see the reference if so, but I suspect it's not possible. Planck derived most of the properties of radiation from thermodynamics alone, but he got the starting point of p=U/3V from Maxwell's equations. Nathaniel Virgo (talk) 10:40, 2 January 2012 (UTC)
thread_title:  Derivation from thermodynamics alone? 

message: F_{SR} = -p_{SR}c_{R}A_{\odot}r_{\oplus\odot} 
is apparently incorrect: for black bodies it yield zero force!
The correct one should be:
F_{SR} = -p_{SR}(1+c_{R})A_{\odot}r_{\oplus\odot}
:The equation was correct, but not useful.  The equation says nothing about black bodies.  It was removed when the section was rewritten. SpaceSailor 03:11, 10 August 2013 (UTC)
thread_title:  Expression for radiation force is incorrect 

message: I am making an effort to tighten up the article.  A lot of things have gotten into it that are out of scope and will be removed.  An explanation of momentum is being added under the photon section. SpaceSailor 20:25, 31 July 2013 (UTC)
thread_title:  Article overhaul 

message: In the section Laser applications of radiation pressure there's a mention of laser radiation pressure being used for fusion research.
The force on the pellet is primarily ablation of the surface.
In fact in many cases, radiation pressure is confused with other effects involving the transfer of real mass - see the Crookes Radiometer for example.
I will revise this paragraph, and perhaps add a reference to Effects Commonly Confused With Radiation Pressure.
Thomasonline (talk) 15:39, 11 September 2014 (UTC)
thread_title:  Radiation pressure not used for fusion 

message: This inserted topic is based on speculative, unsubstantiated pseudo-physics.  A single source from 1968 without any experimental verification is not adequate, and not appropriate for this article--this article is not about speculative physics.  Unless the author of the insert presents some hard evidence and shows acceptance by the physics community, it will be removed. SpaceSailor (talk) 01:49, 17 March 2016 (UTC)
thread_title:  Re: Negative radiation pressure and negative momentum 

message: The vanes spin the same way as a Crookes Radiometer in the video, showing the greater force exerted on the black face rather than the reflective face. Vanes rotating the opposite direction would be expected with a radiation pressure demonstration because more momentum would be transferred to the reflective face on the vanes. I couldn't find a good video of a Nichols Radiometer, so I suggest this video should be removed or replaced with something which illustrates the concept described in this section.  — Preceding unsigned comment added by 67.170.72.164 (talk) 03:24, 10 October 2016 (UTC)
thread_title:  Crookes Radiometer seems to be described as Nichols Radiometer in video under "Radiation pressure by reflection (using particle model: photons)" 

message: I expect that radiation pressure decreases by a factor greater than the square of the radius, because photons would not only spread-out, but also lose momentum or be red-shifted as they go against gravity. This effect would be very small in a low-gravity environment, but near a black-hole, it would be very significant. They pressure would also drop with distance as a result of interaction with interstellar medium. The pressure density would also be affected by dopler effects if the star or accretion disk is rotating, causing the peak-intensity to be offset from the centre of mass. MathewMunro (talk) 00:33, 19 April 2020 (UTC)
thread_title:  Radiation pressure and the inverse-square law. 

message: The article, in particular the "Discovery" section, claims that Maxwell proposed radiation pressure in 1862. I cannot (easily) find a source for this claim. I briefly leafed through Maxwell's personal and scientific letters for 1862 and didn't find anything (although I may have just missed it), and the Nichols & Hunt paper references the treatise from 1873. If anyone knows the correct time and has a source for it, I think that would be beneficial. ChristofferOestfeldt (talk) 15:48, 25 May 2022 (UTC)
thread_title:  Lacking source for Maxwell 1862 claim 

message: We need an explanation for how radiation pressure is explained using the theory of general relativity. OpticalSystem (talk) 17:24, 14 January 2024 (UTC)
thread_title:  Explanation from General Relativity 

message: It has been colonised by people having 'their own theory' and by students who are 'still studying'. No traditional encyclopedia would permit its readers to be confused by amateur opinions, so why should Wikipedia allow it? This is a very 'mature' topic, and no doubt concerning it exists in the minds of physicists. If Wikipedia readers do not understand the subtleties, they should seek out suitable textbooks rather than misleading others. One cannot help but think that the fatuous EmDrive propulsion device was proposed by Roger Shawyer simply because he confused himself by using some of the defective reasoning demonstrated here. 78.145.10.148 (talk) 18:27, 18 May 2024 (UTC)
thread_title:  Proposal to Delete this Entire Discussion