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Re: A riddle
[Re: ventilator]
#95638
10/27/06 03:57
10/27/06 03:57
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Joined: Jul 2002
Posts: 5,181 Austria
Blattsalat
Senior Expert
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Senior Expert
Joined: Jul 2002
Posts: 5,181
Austria
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its not our eyes but the brain and the frequency it needs to calculate what input it gets from the eyes. if our brain would "see" faster we would be able to see bullets shot out of a gun. because its damn slow we need special flare ammuniton for it
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Re: A riddle
[Re: Dan Silverman]
#95641
10/27/06 07:14
10/27/06 07:14
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Joined: May 2002
Posts: 2,541 Berlin
EX Citer
Expert
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Expert
Joined: May 2002
Posts: 2,541
Berlin
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I donīt think lifeforms see in pictures. If something moves very fast we see a blurred mix of endless sequences. Very simple example, if you watch out of the driving train you donīt see every third bush, you see a smeared green line. Or a rotating picture with black and white stripes gets, grey, acutally it doesnt gets grey it gets colorfull, but thatīs still not a single picture, but a mix of endless pictures.
By the way, semimodern video games, have the choice to play them with 50Hz or 60Hz. And with 60Hz it looks indeed more realistic. My teacher always says 30 frames are enough for a prerendered movie, but I think that's is so wrong because we see the interpolated frames as well. The motion blur. I mean if something moves with 60 frames per second in on 1/6second from left outside of the screen to right outside of the screen we should recognize something hushing from left to right. With 30 frames the movement from left to right has interuptions and should be less visible. Yeah itīs moving the same fast, but with bigger interuptions the object should be more invisible.
Itīs like watching somethign when a stroboskob is on isnīt as easy as without stroboskob.
:L
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Re: A riddle
[Re: Dan Silverman]
#95642
10/27/06 08:06
10/27/06 08:06
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Joined: Mar 2006
Posts: 3,538 WA, Australia
JibbSmart
Expert
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Expert
Joined: Mar 2006
Posts: 3,538
WA, Australia
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from what i've heard, the frequency at which our brain interprets the image coming into our eyes is between 60 and 80 hertz. my old software design teacher told me this when i asked him for some help and he said "excuse me" and changed the settings up to 80 hertz and explained that otherwise the image was constantly flickering, from what he could see. a quick look at wikipedia doesn't seem to confirm this, but that's just what i heard.
julz
Formerly known as JulzMighty. I made KarBOOM!
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Re: A riddle
[Re: Dan Silverman]
#95643
10/27/06 08:31
10/27/06 08:31
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Joined: Jul 2000
Posts: 27,986 Frankfurt
jcl
OP
Chief Engineer
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OP
Chief Engineer
Joined: Jul 2000
Posts: 27,986
Frankfurt
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Quote:
This is not true. It can indeed be seen in real life. In fact, my entire family was travelling north on a highway when we were passing an 18 wheeler (a truck). One of my kids became really excited and asked outloud why the front wheels of that truck were moving backwards! We all looked and sure enough the illusion of the wheels moving backwards was very strong! The truck had very shiney rims with many, many nuts/bolts to hold the tire onto the hub. It was a bright day and the light reflecting off the rims was pretty intense. However, the nuts looked as if they were moving in the opposite direction and thus the wheel looked like it was rotating backwards.
Our brain has no fixed 'frame rate' and our eyes have definitely no shutter. Nevertheless, contrary to what I said you can indeed observe the backwards rotating effect in real life. The prerequisite is that something external must then act as a shutter.
The most usual effect is a stroboscobe. When lighting a rotating wheel with a stroboscobe that flashes faster than the rotation speed, you see it slowly turn backwards. If the stroboscobe flashes slower, you can see the wheel slowly turning forward. If you ever have adjusted the distributor arm of a car engine you know the effect.
In the case of your truck, what your kids were seeing was a double reflection. Sun light was reflected from two different wheels into their eyes, and both wheels had a slightly different rotation speed (due to a different diameter). So you probably saw one wheel slowly turning backwards and another one forward. Maybe the other wheel was not directly visible so the backwards effect was predominant.
You can use that effect to ask your kids small riddles, for instance "Which wheel has a newer tire, the backwards rotating or the other one?"
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Re: A riddle
[Re: jcl]
#95644
10/27/06 08:59
10/27/06 08:59
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Joined: Jul 2000
Posts: 11,321 Virginia, USA
Dan Silverman
Senior Expert
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Senior Expert
Joined: Jul 2000
Posts: 11,321
Virginia, USA
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Quote:
In the case of your truck, what your kids were seeing was a double reflection. Sun light was reflected from two different wheels into their eyes, and both wheels had a slightly different rotation speed (due to a different diameter). So you probably saw one wheel slowly turning backwards and another one forward. Maybe the other wheel was not directly visible so the backwards effect was predominant.
While I hear what you are saying, JCL, I highly doubt this is what happened. The affect was on the front wheel and the second wheel on th cab was a bit too far away to cause this affect. The wheels on the trailer did not have shiny rims. I am guessing it is even simpler than you stated. It probably only had to do with the way the light was reflecting off the nuts, onto the rim and back into our eyes. BTW - It wasn't just my children that saw it. I did too. It was quite cool.
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Re: A riddle
[Re: jcl]
#95646
10/27/06 12:07
10/27/06 12:07
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Joined: Jun 2004
Posts: 2,234 Wisconsin USA
FoxHound
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Expert
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Posts: 2,234
Wisconsin USA
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I see this all the time actually. Seems once a car gets past 40mph the wheels seem to go backwards. I'm also very near sighted and wear contacts so this might have something to do with it.
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Re: A riddle
[Re: FoxHound]
#95647
10/27/06 12:45
10/27/06 12:45
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Joined: Jul 2002
Posts: 5,181 Austria
Blattsalat
Senior Expert
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Senior Expert
Joined: Jul 2002
Posts: 5,181
Austria
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of course there is no framerate for our visual organs (nobody said that). the fact that you see blurred hands if you move it fast enough infront of your eyes idicates the speed our brain needs to interprete the visual ("framerate" if you dont mind the word ). i doubt this spinback effect can be seen in real life. because if the wheel turns fast enough it will start to look blurred instead of turning backwards. the strobe effect jlc mentioned (same as the frames of a movie) is what "saves" the position of the wheel. if it fits the alias effect sheme then our brain will interprete it as backwards moving, still standing or forward motion. in real life other optical illusion would be needed i think to achieve this effect (if possible)...something that "burns" or fakes single frames to our visual system as a tv would do (strobe lights maybe) i also doubt it can be seen in real life (at least that easy) though i have never thought about it so far. I will have to take a look today when a car passes by cheers
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