Re: Nuclear Isomer Decay: A Possibility for Breakthrough Space

["John R. Laferriere 671-8316" <John.R.Laferriere@dupontpharma.com>]

In response to my description of my understanding of a radiometer, Bernard
Cohen wrote:

"        --This is dead wrong. Why would gas molecules kick the black side
more than the shiny side?
         The photon hitting the black side is absorbed transferring its
momentum. But the photon hitting the shiny side is reflected backward,
transferring twice its momentum. Thus there is more momentum transferred
to the shiny side."

According to this description, the vane should rotate with the black side
moving toward the light source, but in fact it does the opposite.  The url
that Jerry Falo provided gives an explanation that bears more resemblance to
my description than to the one above.

The gas molecules coming off the hotter black side leave that surface with
more kinetic energy than they started with.  The url explains that this 
layer of warmer gas then provides a stronger push at the vane's edges than
the colder air on the white or shiny side.

Here's that url that Jerry gave:
http://www.public.iastate.edu/~physics/sci.physics/faq/light-mill.html

One final observation: The energy of a photon is hv, and the momentum is
hv/c.  There's a lot more radiant energy available to push those vanes than
there is momentum.


John Laferriere, CHP
john.r.laferriere@dupontpharma.com
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