Alain <ele### [at] netscapenet> wrote:
> Take an empty globe of glass, place a needle holding a light rotor made from a 
> glass axis and holding 3 or 4 blades, white on one side, black on the other. 
> Place the rotor on the needle. Remove all air from the globe. Have ANY light 
> shining on that rotor, even a candle light, and the rotor will spinn. That 
> experiment is over 100 years old!

  AFAIK that's the same kind of flawed experiment as the "measure the weight
of an empty balloon, then fill it with air and then weight it again" which
supposedly demonstrates the weight of air. (In actuality that's completely
silly. It's like trying to demonstrate the weight of water underwater by
weighting an empty balloon and a balloon filled with water: You won't get
any difference. What this air balloon experiment actually demonstrates is
the compressibility of air and that compressed air inside the balloon has
a higher density.)

  AFAIK that "experiment" does *not* work in complete vacuum and, moreover,
makes the blades rotate in the wrong direction. The real reason for the
rotation is that the black sides get heated while the white sides don't,
and the heated black sides heat up the air close to them, making the air
push that side of the blade.

  AFAIK photon pressure would not be even near enough to cause the rotation
of such small blades with such (relatively) huge mass.

-- 
                                                          - Warp

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