On Jul 17, 7:53*am, Smitty Two wrote:
In article
,
*harry k wrote:

The number of each feature doesn't matter. *Look at a bicycle wheel
again. *Many spokes (one would do) but only 1 valve stem. * The drill
and all parts are all turning the same *rpm . *The features all appear
at the same time because they all come around together. * The ones
being illuminated *repeat all at the same repetition rate, I have been
puzzling all day how to explain that better but can't come up with a
way.

Of course the number of features matter. This is the way the illusion
works:

In your mind, superimpose a four-spoke wheel on a clock face, with
spokes pointing to 12,3,6, and 9. Label the spokes A,B,C, and D,
respectively.

Now, turn the wheel clockwise. Let's say you turn it 1/6 revolution,
a.k.a. 60 degrees, a.k.a. "two hours" of rotation. So A is pointing to
2, B to 5, C to 8, and D to 11.

But during the rotation, turn off the light, close your eyes, whatever.
Now what happens in the mind is that it misinterprets what the eye sees.
It makes more sense to the mind that the spokes have each moved
backwards one hour, rather than forwards two hours.

So you think that A moved from 12 to 11, rather than from 12 to 2. Of
course, it isn't A that you're seeing at 11, it's D. But A and D look
the same, because they're identical spokes.

The mind wants to believe that while the lights were out, things moved
as little as possible. So it sees the rotation slowly in reverse, rather
than more quickly in forwards.

Now superimpose another set of different features, but say there's six
of them instead of four. Call them A2, B2, C2, D2, E2, F2. Now with each *
60 degree rotational increment, each of those features also moves "two
hours." But they were already at 2 hour increments from one another (as
opposed to 3 hour increments for the 4-feature set.) So now, A2 takes
the exact place of B2, B2 takes the place of C2, etc. Result is that
this feature set will appear to stand still.

Finally let's look at a ten feature set, A3 through J3. Now they don't
all start out lined up with clockface numerals. A3 is lined up with 12
o'clock, and F3 is lined up with 6 o'clock, but the rest of them are
some fractional hours. So it will be easier to consider degrees of
rotation instead of clock readings.

360 degrees / 10 = 36 degrees. The last "spoke" (J3) in this feature set
is located at 360 - 36 = 324 degrees. After one 60 degree incremental
movement, A3 will be at 60 degrees, and J3 will be at 24 degrees. The
mind wants to see minimal change of position, so it now sees J3 as A3,
and believes that the wheel is rotating slowly clockwise (24 degrees per
increment instead of 60)

So, if you've followed this along, I hope you can see that the number of
features is critical to whether the mind sees forward motion, backward
motion, or a standstill, and that the apparent motion, either forwards
of backwards, is also slower than what's actually happening.

In the commercial, the different parts of the drill have different
numbers of features, so can't exhibit the same illusion at the same RPM.

I repeat. Teh strobe takes a "still picture" not a moving picture.
If it is timed to show reverse rotation then the same features _all_
of them visible will be in the right location each time the strobe
fires.

You can keep fighting it but you are wrong. Visit your local HS and
talke to the physics teacher, I have resorted to that in the past and
found out I was wrong on a point once.

Harry K