does the frequency of light have to something to do with it?
2006-07-27 15:40:49 · 7 answers · asked by anony m 1 in Science & Mathematics ➔ Physics
Discharge light sources like fluorescent bulbs or street lighting actually flicker on and off 60 times per second. They flash so fast that you normally can't see the strobing.
When a wheel is spinning at 60 rps, the wheel will be in the same position every time the light flashes on, so it will appear to stay still. When the light flickers off, the wheel completes its cycle: but you can't see it do that because the light is off.
If the wheel is going slightly slower than 60 rps, it will appear to rotate backward.
If you get a fan and a variable speed strobelight you can have hours of fun by yourself in a dark room... I need to get a life...
2006-07-27 15:55:05 · answer #1 · answered by spagmess 2 · 3⤊ 1⤋
In fact the human eye has a refresh rate that varies from person to person. Thus we don't see the world as it moves continuously, but in discrete chunks. For example: Say you are watching a wheel spinning clockwise, and say your eye sees a spoke at the twelve o'clock position, and then your vision refreshes when the spoke has traveled all the way to the 11 o'clock position. Even though you know the wheel is spinning clockwise, your brain will assume it is spinning counter-clockwise because it saw the spoke the second time only a few degrees away from where it saw it the first time, thus this is the easy assumption. The next time you see the spoke it will be in the 10 o'clock position, and you will again think it is moving backward. Think about it for a minute, you will get it.
2006-07-27 15:51:06 · answer #2 · answered by 1,1,2,3,3,4, 5,5,6,6,6, 8,8,8,10 6 · 0⤊ 0⤋
Frequency of light determines its color and has absolutely nothing to do with the effect you describe.
The human brain, much like a video camera does, creates the illusion of motion from a fast series of still images taken by the eye. In video that's normally 30 frames per second, but in the human eye, it's about ten "frames" per second. Thus, if the wheel turns at a speed slightly slower than 1 revolution per tenth of second, the "second frame" will show the wheel's spikes like they moved a bit backwards. Now if every frame gets the wheel's spikes as if they moved a bit backwards, you get the illusion that it's moving backwards.
You can check this by looking at an accelerating car, you'll notice that you get the effect only after the car reaches a certain speed, then the wheel seems still, then it seems that it's moving slowly forwards, and then the effect disappears.
2006-07-27 15:56:26 · answer #3 · answered by Sinelnic 1 · 0⤊ 0⤋
It's the same thing with car wheels and propellers. I see it all the time and I've wondered the same thing. The tv thing may be right but it happens with the naked eye too. Is that the same principal? I don't know the scan or refresh rate of my eyes :-)
2006-07-27 15:47:15 · answer #4 · answered by AK 6 · 0⤊ 0⤋
yes..
It's called the wagon wheel effect...
and you're exactly right.
the scan rate of tv which is 30 time a second for the first field, and then the second... favors the spoke that has just past being highlighed... so it appears to move BACKWARDS.
2006-07-27 15:43:30 · answer #5 · answered by Anonymous · 0⤊ 0⤋
No. But the frequency of the scanning rate of the camera does.
2006-07-27 15:42:38 · answer #6 · answered by Anonymous · 0⤊ 0⤋
its an illusional effect.
2006-07-27 15:43:27 · answer #7 · answered by millikant02 1 · 0⤊ 0⤋