Wheels Turning Backwards in Video
11-27-2011, 06:43 PM
#1
Карты убийцы
Thread Starter
Wheels Turning Backwards in Video
What's the scientific explanation of seeing the wheels turning backwards in videos. Some wheel patterns seem more visible than others.
What's weird is I see this effect on video, but can not see it in person.
What's weird is I see this effect on video, but can not see it in person.
11-27-2011, 06:45 PM
#2
Rooting for Acura
iTrader: (1)
Good question. I always wondered about this myself.
edit: here is one theory
http://askville.amazon.com/car-wheel...equestId=42753
edit x2: Yeah, I think that just about sums it up. Plenty of good responses there.
edit: here is one theory
http://askville.amazon.com/car-wheel...equestId=42753
edit x2: Yeah, I think that just about sums it up. Plenty of good responses there.
Last edited by knight rider; 11-27-2011 at 06:48 PM.
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phee (11-28-2011)
11-28-2011, 09:54 AM
#4
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Not a very complicated concept.
Video works by taking however many frames per second. If you're recording a wheel spinning, and the wheel completes just under one rotation each time the camera takes a frame, the wheel will be just behind where it was the previous frame. And then in the next frame, it'll be just behind what it was before, and so on. Link all the frames together, and the wheel will look like it's rotating backwards.
The time it takes for the wheel to complete one full rotation is slightly more than the time between capturing frames.
Reason you can't see it with your eyes is because obviously your eyes don't work by taking hundreds of pictures per second.
Video works by taking however many frames per second. If you're recording a wheel spinning, and the wheel completes just under one rotation each time the camera takes a frame, the wheel will be just behind where it was the previous frame. And then in the next frame, it'll be just behind what it was before, and so on. Link all the frames together, and the wheel will look like it's rotating backwards.
The time it takes for the wheel to complete one full rotation is slightly more than the time between capturing frames.
Reason you can't see it with your eyes is because obviously your eyes don't work by taking hundreds of pictures per second.
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hANDYcaptd (11-28-2011)
11-28-2011, 10:25 AM
#5
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You can see an example with your eyes, as a car on a dyno with the building lit by florescent or LED lights. These lights have a frame rate and you can get the same effect.
11-28-2011, 10:34 AM
#6
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11-28-2011, 10:39 AM
#7
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Bingo, blink fast and you've just simulated it.
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11-28-2011, 11:01 AM
#8
video tends to be 30 fps. in between these frames there is a period of darkness, during that darkness the wheel continues moving and it make it look like the wheel is moving backwards because the location of spoke A is moving faster than the frequency of the frame rate
11-28-2011, 12:42 PM
#10
Senior Moderator
Airplane props do the same thing on video.
11-28-2011, 01:54 PM
#11
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With an iPhone the propellers fly off.
http://www.youtube.com/watch?v=1iPnHyBdctA
http://www.youtube.com/watch?v=LVwmtwZLG88
Magic Helicopter:
http://www.youtube.com/watch?v=rVSh-au_9aM
Last edited by Bearcat94; 11-28-2011 at 01:56 PM.
11-28-2011, 03:01 PM
#13
Senior Moderator
Great examples.
11-29-2011, 12:11 PM
#15
Chapter Leader (Southern Region)
Such a troll thread. 
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