Re: radiometer vs. light mill

[John Denker <jsd@MONMOUTH.COM>]

At 09:28 AM 5/18/00 -0400, Chuck Britton wrote:

> (I'll not bring up my continuing disbelief in this list's PC
> explanation of the Light Mill's driving force - but they MIGHT be
> related IF heating were the cause?!)

*Any* simple PC (politically correct) explanation of such devices is
probably not PhC (physically correct).  There are two kinds of thing that
spin in response to light.  I've seen them in operation side by side.

If the device is in a hard vacuum, it spins one way due to simple light
pressure (momentum).

If the device is in a soft vacuum, it spins the other way due to heating
(energy).

For homework, ask yourself:  what is the energy-per-momentum ratio for
light?  Is that smaller or larger than what students might expect based on
other momentum flows they have experienced?