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Andrew Buren
- 18
- 0
This is another thing that I have trouble figuring out. Why do the spokes on a wagon seam to rotate backwards at certin speeds?
Help!
Help!
Vanadium 50 said:Have you ever seen this? I have not. I have seen film of this, but that's a different question.
Later and current turntables have a built in strobe and the speed pattern on the side of the turntable.TVP45 said:Long ago when Hi-Fi enthusiasts worried about turntable speeds, there were poor-man's strobes that looked something like an optical encoder disk that you could put on the turntable and view under a fluorescent light. Depending on the speed, it went forwards, stood still, or went backwards.
TVP45 said:Now, how you get your Conestoga wagon under a fluorescent light is another.
mgb_phys said:There's a similar effect giving the stretched wheels on racing cars in early movies.
The shutter in early film cameras is a slit in a wheel that rotates in front of the film.
As it turns it exposes the top of the image first and then the next slice below it and finally the bottom.
So between the time when the top of the wheel is photographed and the bottom the car has moved forward and so the wheel looks like it is stretch backward at the top and forward at the bottom.
Cartoons draw this effect exaggerated to make the car look fast, but usually draw the wheel forward at the top.
ps. You can show the 'frame rate' of your eye in a dark room by swinging a flashlight or laser pointer at arms length. You will see a series of lights rather than a continuous blur.
Depending on the lighting etc your eye runs at around 15fps.
mgb_phys said:I love the dancer illusion, try staring at it and relax-let your eyes go to infinity
when you focus again you can get it to switch directions.
pallidin said:The dancer illusion is awesome!
I am able to switch directions as well as have it appear to go back and forth.
I heard it said here that it's a left/right brain thing.
What I wonder is if it's healthy to do this. Maybe it would be a great tool for brain strengthening, or maybe it would fry what few brain cells i have left.
Anyone know?
Scroll the picture up until you can just see the dancers foot or just focus on the dancers foot. Without the front + back information it's easier to see imagine the dancer turning the other way. Once you get the foot to appear to be spinning counter clockwise, scroll the picture down slowly or stop looking at just the foot. The dancer will appear to be spinning towards her right if you imagine she is standing on her left leg, and vice versa. Once the model appears to be spinning in a particular direction, my brain "expects" the motion to continue so it's difficult for me to mentally change the direction unless I look away for a brief moment, because to change direction, the dancer has to instantly change which foot she's standing on (and instantly change angular momentum). If I focus on the foot, I can imaging the image changing direction back and forth by imagining either the heel or the toes are always pointed towards me or to the side.leroyjenkens said:I can only see that dancer spinning clockwise. I've tried everything to make it look like she's spinning counter-clockwise and I just can't seem to do it.
I see streaks (so do most people), not a series of lights, unless the light source is pulsing.mgb_phys said:You can show the 'frame rate' of your eye in a dark room by swinging a flashlight or laser pointer at arms length. You will see a series of lights rather than a continuous blur.
The Dagda said:Someone who is autistic can't sense optical illusions generally, why do you think that might be?
pallidin said:Good point.
Dagda, I recall a specific illusion involving optically switching left/right viewing by a headset mirror arrangement.
This causes, say, bumps in a road to appear as depressions, and holes to appears as "bumps"; among other odd visual consequences.
What disturbed me is that I read continued use could result in a lasting(though not permanent) reversal after using the headset.
These levels of illusions are very powerful.
Similarly, as mentioned before, I wonder if actively practicing left/right brain switching is a good thing, or not.
leroyjenkens said:I can only see that dancer spinning clockwise. I've tried everything to make it look like she's spinning counter-clockwise and I just can't seem to do it.
robphy said:
The phenomenon of the spokes on a wagon appearing to rotate backwards is known as the "wagon-wheel effect." It occurs when the frequency of the rotation of the wheel is similar to the frequency of the camera's frame rate. This creates an optical illusion where the spokes appear to be moving in the opposite direction of the wheel's rotation.
The frequency of the camera's frame rate is directly related to the perception of the wagon-wheel effect. If the frame rate is too low, the illusion will not occur. However, if the frame rate is close to the frequency of the wheel's rotation, the effect will be more pronounced.
Yes, the wagon-wheel effect can also be seen in other moving objects such as car wheels or helicopter blades. As long as the frequency of the object's rotation is similar to the frame rate of the camera, the illusion will occur.
The wagon-wheel effect is a real phenomenon that is caused by the way our brain interprets visual information. While it may seem like the spokes are actually moving backwards, they are in fact moving in the same direction as the wheel's rotation.
The wagon-wheel effect can be reduced or eliminated by adjusting the frame rate of the camera or by using a different type of camera with a higher frame rate. It can also be prevented by using a strobe light to "freeze" the motion of the wheel, making it appear as though the spokes are not moving at all.