>>> Why do you think that those frequencies are far above 50 Hz?
>>
>> My engine *idles* at several thousand RPM...
> The significant character here is 'M'

Hmm. What is 2,000 RPM in Hz? 33 Hz? That's interesting...

>>> What sound does your motor make? Can you find the base frequency on 
>>> your keyboard?
>>
>> Surely that's just the resonant modes of the exhaust system and the 
>> chasis?
>>
> Whatever it is, that is what you see. If it moves faster than 50 Hz you 
> either see it not moving at all or, viewed in the right direction, as a 
> semitransparent surface.

AFAIK, the retina sees the "integral" of incident light over time, 
roughly. So I'm not sure why an object moving fast enough would appear 
to stop moving. Become invisible, perhaps, if it's small enough...

> If you can prove that you can see something 
> moving at, say 200 Hz, I have a couple of friends working on the retina 
> that would be most interested in such a physiological anomality. ;)

How about my tuning fork? That says "440 Hz" on it, and I can see that 
vibrating plainly enough... ;-)

(Oddly though, it doesn't seem to make much audible sound, despite the 
ends of the fork traversing really quite some distance. I can only 
surmise that it doesn't move the air around very much or something...)

-- 
http://blog.orphi.me.uk/

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