Xref: utzoo rec.autos:5910 talk.bizarre:6116 alt.flame:893
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From: ulrich@grasp.cis.upenn.edu (Nathan Ulrich)
Newsgroups: rec.autos,talk.bizarre,alt.flame
Subject: Re: Truly relevant discussion
Message-ID: <2770@super.upenn.edu>
Date: 9 Dec 87 18:57:54 GMT
References: <4134@bellcore.bellcore.com> <7106@sunybcs.UUCP>
Sender: news@super.upenn.edu
Reply-To: ulrich@grasp.cis.upenn.edu (Nathan Ulrich)
Organization: University of Pennsylvania
Lines: 37

In article <7106@sunybcs.UUCP> ugjeffh@joey.UUCP (Jeffrey Horvath) writes:
>In article <4134@bellcore.bellcore.com> tr@wind.UUCP (tom reingold) writes:
>>
>>What color should my interior of my car be to make my car go faster?
>
>  Why, I should imagine that you would want the interior parts that face
>foreward to be white, and the backwards facing parts to be black.
>
>  Reasoning:
>
>The black would absorb the energy of the light, thus transferring your energy
>to the car in the forward direction.  The white would reflect the light, thus
>reflecting potentially harmful backwards thrust. :-)

No, no, no.  According to what I remember of my statistical thermo, you want
the *rear* of the car to be white.  That way you take advantage of the transfer
of momentum from the photons striking the car.  If the surface is white, then
the momentum transferred to the car per photon will be 2mccosT, where m is the
mass of the photon, c is its velocity, and T is the angle of incidence.  If
the surface is black, then most photons will be absorbed, transferring only
mccosT momentum per photon.  Therefore, if the front is black, the back is
white, the sides are any color, and we neglect the top, and there is equal 
amount of radiation from all sides, then we have a net transfer of 
		mccosT times the photon density then integrated from 0 to pi.

This must be of huge significance--think of the huge number of photons striking
your car every second....

Of course, to *really* move, you should put the back (white) side of your car
to the sun. :-) :-) :-) :-) :-) :-) :-) :-) :-) :-) :-) :-) :-) :-) :-) :-) 

(by the way, I think this is how the outer space "sun-sailers" work, by using
the photon pressure to move spacecraft....it really is a measurable phenomenon)


Nathan Ulrich
ulrich@grasp.cis.upenn.edu