Subject:
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Re: Hypothetical design question
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Newsgroups:
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lugnet.space
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Date:
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Thu, 26 Jun 2003 21:26:53 GMT
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Viewed:
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709 times
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In lugnet.space, George Haberberger wrote:
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No, light does exert force.
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Correct.
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Have you ever seen those little glass bulbs with
black and white squares of paper mounted on arms? Something sets them
spinning.
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Yes, *something* does. It’s not light though, since if it was light, they would
spin in the black direction (with the black side leading the rotation).... (the
momentum imparted to something perfectly reflecting is twice that of something
being absorbed)
Instead, the spin in the white direction, and that’s because they are in an
imperfectly evacuated chamber... what imparts motion is the differential between
air temperatures on the black side and the white side. The black, absorbing
energy, heats up air near it more than the white, reflecting energy, does.. and
the air, bouncing off the black paddle and having much more mass than a photon
does, swamps the momentum differential transfered by the reflected light that
would tend to push it the other way
see here, for example:
http://www.theharrowgroup.com/articles/20030505/20030505.htm
(then search for the word black and read in that area)
You guys need to learn to google better, IMHO.
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Also, a solar sail uses light propulsion, cf. Attack of the Clones and The
Mote in God’s Eye.
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Yes. IIRC someone was going to actually test one of these in real life but I
dunno if it happened or not.
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Message is in Reply To:
 | | Re: Hypothetical design question
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| (...) No, if you use simple conservation of momentum, at subrelatavistic speeds, you can still get a modest boost with a propellant speed of 2 mph. Your speed increase is propellant weight x 2 mph / remaining vehicle weight. since total momentem has (...) (21 years ago, 26-Jun-03, to lugnet.space, FTX)
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