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I’m stumped

  1. Jun 26, 2006 #1
    I opened the garage doors and turned on a pair of 150-watt incandescent (note INCANDESCENT) floodlights to admire a torrential thunderstorm and newly created river rushing down my driveway.

    What amazed me most was a strobe effect on some of the raindrops. There was little or no wind, the droplets seemed to fall at 4 different rates. The slowest, presumably smallest, fell only a few feet per second like very fine snow. The next fell at a rate that one could track continuously as it passed through the floodlight beam. Others seemed to draw a line as they passed through the beam similar to a meteor trail. The fastest drew a DIScontinuous line as they passed through the beam. As they passed at about two meters in front of me, they formed a broken line segment about 2 cm bright, 2 cm invisible, exactly as one would observe if they were illuminated by a strobe lamp. The only illumination was the incandescent flood lamps (no dimmer in circuit). The strobe effect seemed only to occur with the fastest (largest?) droplets.

    I can’t think of anything that would cause this.
     
  2. jcsd
  3. Jun 26, 2006 #2

    Danger

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    Drugs?[color=#eded]....[/color]
     
  4. Jun 27, 2006 #3
    No thanks.
     
  5. Jun 27, 2006 #4
    Maybe you are seeing different droplets reflecting light to your eyes..maybe a few different droplets appear as one droplet dropping to the ground. Just a theory...
     
  6. Jun 27, 2006 #5
    Maybe there is a slight strobe like effect from the incandescent lights due to the alternating current of the power source?

    "[URL [Broken] ]http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00Bh5c&tag= [Broken]

    This page seems to support this hypothesis.
     
    Last edited by a moderator: May 2, 2017
  7. Jun 27, 2006 #6

    DaveC426913

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    Link busted (an extra http// in there). Here is the correct link:

    http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=00Bh5c&tag="" [Broken]

    Unfortunately, it does NOT support the strobe hypothesis, since the objects in the SUV picture are not being lit by any strobe source.
     
    Last edited by a moderator: May 2, 2017
  8. Jun 27, 2006 #7

    DaveC426913

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    I put forth the following hypothesis:

    The first three size of drops are not doing anything out of the ordinary:
    - Small drops are falling slowly like snow,
    - Medium drops are falling fast enough to track,
    - Larger drops are falling fast enough to be a blur
    So, the only thing needing explaining is the fourth type, the discontinuous line.

    I submit that the discontinuous trails are a trick of the eye. The eye does not move smoothly, but jerks very rapidly - faster than we are conscious of. This is known to produce stroboscopic effects under the right circumstances.

    I'd go further, to suggest that the difference between types I-III and type IV is a matter of what you are trtying to focus on - something moving or something still. I'd bet that you couldn't see types I-III and type IV simultaneously (though you may not realize it).
     
  9. Jun 27, 2006 #8
    It seems a camera can detect the warming cooling cycle and I have seen he effect on film before but never took note of it. I just now dimmed a halogen lamp using a common residential dimmer control. I dimmed it to the point where it extinguished if dimmed any further. I could easily count the turns in the coiled filament. I could not discern any flickering even if I shook my head rapidly.

    Any links?
     
  10. Jun 27, 2006 #9
    Try waving your hand rapidly back and forth in front of the light source, Geniere, and compare with the same in front of the TV in a darkened room.

    Oh go on then, I've just run out back and looked at the spray from the hosepipe in torchlight. There did seem to be something of a morse-code effect with some dots and some dashes. Interesting.
     
  11. Jun 27, 2006 #10
    Been doing that since 1946 when my dad got our first TV.
    Using a garden hose (good idea-thanks) and floodlights I was able to duplicate the strobe effect. It required adjusting the hose nozzle to obtain large droplets. The effect was not quite the same in that the bright/invisible components of the trail were about 4cm rather than 2cm. I attribute that to the droplets moving slower.

    My 3 million candlepower flashlight (torchlight?) decided not to work tonight so I tried to use my SUV’s headlights to eliminate the possibility of the effect being caused by 60hz ac power. Using the garden hose and the headlights, I did discern the effect; at least I think I did. I need to find a way to eliminate glare and use a wider part of the beam.

    My theory of the moment is that the droplets are oscillating as they fall
     
  12. Jun 27, 2006 #11

    DaveC426913

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    Oscillating how? And how would that cause the effect?
     
  13. Jun 27, 2006 #12

    Mk

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    Drugs?... ................
     
  14. Jun 28, 2006 #13
    No longer stumped!

    No longer stumped!

    http://www.highbeam.com/library/docFree.asp?DOCID=1G1:3670324
     
  15. Jun 28, 2006 #14
    Good one, Geniere. We learn something new every day!
     
  16. Jun 28, 2006 #15

    DaveC426913

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    Wow. Talk about getting the answer to your question...It's like they wrote that just for you.
     
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