I have also seen this effect on You Tube in clips of helicopters, especially when their rotor blades are starting up, and reach a certain RPM. Sometimes looks like the rotors are turning very slowly, or not at all. I saw a clip where it appeared as though the helicopter was flying with the rotor blades barely moving.
Back in the olden days, there was one record label (Epic, I think) that had a ring of black bars around the edge of the label (pointing outwards from the center) which appeared stationary if you looked at the record under fluorescent light while it was rotating at precisely 33 1/3 RPM. That way you could tell if your turntable was at the correct speed.
Nah, it’s pretty common: You’ll see it any time you have a strobing light source (which a lot of them are) and something turning fast (like car wheels).
Actually it’s pretty common in real life. Happens w/sunlight, no 120Hz streetlights needed. But only works with truck tires having chrome lug nuts. If you commute on a highway, start watching for backwards-moving lug nut patterns. “False Strobe Effect.”
If the nuts were tightened with a tire iron, they all end up at about the same angle. When the tire then spins, the flashing chrome facets march backwards slowly. If the nuts were tightened with an air tool this won’t work, since they’ll be positioned randomly.
Go chuck a dvd in a drill so you can spin it, then stick ten hex nuts spaced evenly around the rim. If they all point inwards, then when you spin the disk, the flash of the facets will remain still. By positioning the nuts so you advance or retard the rotation as you go from nut to nut, you can force the “flash” to drift forward or back.
Oddly, if all six nuts are adjusted parallel to the same line, this gives a backward drift effect.
…should be ALL TEN HEX NUTS ADJUSTED
Here’s youtube, but since video aliasing interferes with the “non-strobe” pattern, you’ll really have to build and observe your own model.
http://www.youtube.com/watch?v=6LRnJIPoF9w
How is this NOT a strobe effect? With a strobe, you get a ‘beat,’ where the rotating object seems to come to a stop and reverse directions. But with the flashing lug-nuts effect, this never happens. The nuts always move backwards, and if you spin the disk faster and faster, the nuts always appear to speed up. There is no magic RPM where the pattern seems to come to a stop.
Thanks for confirming this. I’d noticed this effect personally and was dismayed when one of the world’s self-appointed top vision experts informed me I was mistaken. :smack:
Discs were made and used in those days with rings of black bars, each ring with different spacing timed for different rotational speeds: 78 RPM, 45, 33 1/3 and 16 2/3, exactly for that purpose. If you saw it on a record label, they were just copying it.
Some turntables also had timing bars painted on or viewable thru windows.
Maybe a bit OT, but what the hell- A highway in Texas. A row of evenly placed, rather roundish trees along the roadside. Just beyond the trees a railroad track ran parallel to the highway. The setting sun shone through the spaces between slowly moving boxcars and the trees appeared to be rotating. It was both weird and cool.