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Hubcabs (or helicopter or airplane props) do that - they spin one way-slow
down-reverse-speed up-slow down etc when you see them on TV, because the
frame rate of the video camera is "interfering" with the rate of wheel
motion; for example, suppose the TV camera waits 0.033sec between frames. In
that amount of time, the spokes of the wheel might turn enough that each
spoke ALMOST lines up with the position of the spoke that used to be there.
If this occurs, each successive frame of video will show the spokes moving
slightly BACKwards. However, if the wheel is changing speed you will observe
the speedup-slowdown effect.
The effect of waving your fingers or spinning a prop in front of the monitor
works the same way. The monitor refresh rate is about 70Hz. In fact, it's
probably (not sure cause I've never tried it) possible to calulate the speed
of the propellor using the "observed speed" and comparing it to the known
refresh rate of the monitor.
This effect is kind of like in early science when the value of the speed of
light was still under experiementation. Scientists tried to measure c using
several spinning apparatuses, incluing a light beam bouncing off an
octagonal arrangement of mirrors spinning at high speed, or a beam of light
passing through the narrow notches in a rotating gear.
I kinda rambled on a bit, but I just thought it was interesting.
Dan Simonson <Jedi101673@aol.com> wrote in message
news:G2JnwM.ByF@lugnet.com...
> That's wierd. If you notice on the higway though car hubcaps do the
> samething. It's cool illusion though.
>
> --
> Chef
> ICQ:84584424
> AIM: Jedi101673
> http://members.xoom.com/legobase
>
>
> Bradley Dale <dinosauria_ca@yahoo.ca> wrote in message
> news:G2Hyx3.Fu6@lugnet.com...
> > To answer: Is my computer emitting abnormal magnetic fields?
> >
> > Materials needed: 8504 Jet Throwbot (or LEGO toy with similar • propellor),
> your
> > computer
> >
> > Directions:
> > 1. Stand away from the computer.
> > 2. Spin the propellor by tapping on one side
> > 3. Note the direction of spinning.
> > 4. Now hold the propellor up against the monitor.
> > 5. Spin in a similar manner
> > 6. Observe.
> > 7. Reply to this message.
> >
> > I was playing with Jet near the computer, and when I spun his propellor • it
> > changed direction and acted weird. It doesn't do this when its not near • the
> > computer. Is this normal (safe?), or do I need a new monitor? This • isn't
> > exactly LEGO-related, but I just want to see if this happens to other
> people.
>
>
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