Some people claim that they've seen stroboscopic effect in truck wheels on the highway. Supposedly the wheels look like they are turning backwards slowly. SUpposedly this occurs in sunlight, NOT under streetlights which flash at 120Hz, and NOT with the truck driving past with changing angles.
Well, a "great" mystery is solved! :) I finally saw the effect myself. The cause is pretty obvious. The backwards motion comes entirely from the flashing facets of the lug nuts on the wheels. Trucks have ten lug nuts, and if the flashes from the hex nuts occur at slightly different locations for each nut, then we might see a pattern which moves at a different speed than the wheel. The lug nuts must be oriented in organized fashion. If they've been applied with an air wrench, they will be randomized, and no "strobe patterns" will appear. The simplest pattern is to orient all the lug nuts radially. This produces reflections which remain static as the truck wheel spins. If instead we twist the first nut by 6deg, the next by 12deg, etc., then the tenth nut will twist by 60deg or one hex facet. Spin this wheel, and we see a rotating light pattern which moves 6x slower than the spinning wheel. We can make the pattern go backwards or forwards depending on which way the lugs were turned. Now here's something weird. If we twist the nuts by -36deg each time, then all the nuts will be aligned parallel to a single parallel line. This orientation gives a flashing pattern, but also products a backwards drifting pattern as the wheel rotates. This orientation of nuts would occur naturally if the nuts were tightened with a tire-iron. (If you step on the handles of the tire-iron so it tilts to the same angle each time, then all the nuts will be aligned parallel.) I made some spinning disks with lug nuts stuck on with foam tape. Take a look at the youtube videos: Nuts aligned parallel (the tire-iron tightening pattern.) http://www.youtube.com/watch?v=78Mc9kg2kU8 Improved version (progressive 6deg twists) http://www.youtube.com/watch?v=6LRnJIPoF9w So... it looks like the "strobe effect" pattern on truck wheels is entirely real, and is most probably a naturally-occuring effect which happens whenever someone tightens the nuts with a tire iron and not an air-wrench. And by setting the nuts to an improved orientation, much more clear and obvious patterns can be produced! PS I bought a thermal camera: http://www.youtube.com/watch?v=bQPUzPXKRuU http://www.youtube.com/watch?v=SJ-8yFgWt-c http://www.youtube.com/view_play_list?p=6E21BC6820E062A6 (((((((((((((((((( ( ( ( ( (O) ) ) ) ) ))))))))))))))))))) William J. Beaty SCIENCE HOBBYIST website billb at amasci com http://amasci.com EE/programmer/sci-exhibits amateur science, hobby projects, sci fair Seattle, WA 425-222-5066 unusual phenomena, tesla coils, weird sci
