🚀 go-pugleaf

In article <4bbqu6$r2q@marina.cinenet.net>, vergon@cinenet.net says...
>
>Ross Tessien (tessien@oro.net) wrote:
>: In article <4b6p20$bm7@scotsman.ed.ac.uk>, ajc@reaxp01.roe.ac.uk 
says...
>: >
>: >In article <4b6nep$gu3@ixnews2.ix.netcom.com>,
>: >Alan \"Uncle Al\" Schwartz  <uncleal0@ix.netcom.com> wrote:
>: >>The radiometer is under a light vacuum.  Heating of the black side 
of 
>: >>each vane launches mass convection currents with sufficient 
orthogonal 
>: >>component to drive the vanes.
>: >
>: >        what is the fine detail behind the phrase `convection 
currents'?
>: >
>: >        i guess that the dark side of the vane is heated by radiation
>: >        and so any air molecule that collides with the vane is heated
>: >        slightly and then leaves with more energy that it arrived (on 
>: >        average).  this gives a net loss of momentum to leaving 
>: molecules
>: >        and so the vane moves in the opposite direction.
>: >
>: >        (you could think of the process as molecules being held on 
the
>: >        surface, heated, and released like the gas flying out of a
>: >        rocket.)
>: >
>: >        alternatively, if the mean free path of molecules is less 
than
>: >        the size of the vane, then these heated molecules remain to 
the
>: >        dark side of the vane for a few collisions, giving a locally
>: >        increased pressure.  (i'm automatically suspicious about this 
>: because
>: >        it's talking about gas that's not in thermal equilibrium).
>: >
>: >        i think these are two separate processes and i don't know 
which
>: >        dominates, or if `convection currents' implies some other 
>: process -
>: >        any comments?
>: >
>: >        andrew
>: >
>: >-- 
>: >           work phone/fax: 0131 668 8356, office: 0131 668 8357
>: >    institute for astronomy, royal observatory, blackford hill, 
>: edinburgh
>: >                     http://www.roe.ac.uk/ajcwww
>: 
>: 
>: Well, all of the previous comments are excellent in this post and the 
>: others addressing the question.  Let me take the phenomena one level 
down 
>: in detail to show where the force originates in each of the two kinds 
of 
>: radiometer.
>: 
>: The first kind of radiometer is a reflective one.  It requires a very 
>: good vacuum and is not normally sold as a science toy so I doubt this 
is 
>: the kind the teacher has.  But lets consider it any way.  Normally, to 
>: maximize the effect, one has a black surface on one side and a highly 
>: reflective surface on the other.  White paint meerly decreases the 
>: effeciency of the effect but in space would work fine.
>: 
>: Now the energy imparted by a photon colliding with the black side of 
the 
>: surface and being absorbed is one times its momentum.  This is given 
by 
>: its relativistic mass times velocity, or, U = mc
>
>Then you agree, a photon that has mometum has mass.
>
>That's where this whole subject of radiometers started.
>
>
Always have, always will.
Ross Tessien
	There exist in nature, no attractive forces.



>
>VERTNER VERGON -
>
>Who indisputably re-established the existence of radiant mass.
>Who indisputably corrected two errors in the special theory of 
relativity.
>Who produced the final solution to the twins paradox.
>
>And who developed a successful model for QED.
>