Stephen A. Lawrence wrote:
Terry Blanton wrote:
From: Harry Veeder>
In reality the wavelength (and consequently momentum) of the
reflected photon
is slightly less than the wavelength ( momentum ) of the incoming
photon.
That should say "slightly longer" instead of "slightly less"!
But, but, but, that means the sail should be black not reflective,
right?
No. If it's reflective, it absorbs all the incoming momentum.
OOPS I meant "If it's black, it absorbs all the incoming momentum".
(And energy, too, of course.)
For each photon with momentum "p", a black sail absorbs momentum of "p".
But if it bounces the photons off, a reflective sail picks up momentum
of (almost!) 2*p from each photon. So it absorbs _twice_ the incoming
momentum.
