Why do high speed wheels sometimes look like they re reversing?

It's not a physical phenomenon.

It's caused by the human eye focusing on one point.

If there is a bit of b c d e f g h i on the wheel.

And the point that the eye sees is a

Then when the wheel is spinning rapidly, b c d e f g h. These dots will all pass through a split second

The human eye cannot keep staring at a point on the wheel (say B) because the eye cannot turn that fast.

So we'll see b c d e f g h i . The remnants of the image.

Then you will see that the wheels are not moving.

As for the inversion, it's actually another level of eye illusion.

It's like the rising circle of color in front of the barbershop.

Because the remnants of the approaching points are almost the same, and in some places people are not looking at them in focus, so it looks like the wheels are moving backwards.

It's just a magic trick of the eyes.

The above is my speculation and is not necessarily authoritative Comments are welcome.

Fast speed, visual residual problems (such as only 1ms can be seen at the minimum).

For example, if you turn 359 degrees per second, then you see that it is 1 degree.

Because people have visual residues.

I don't know, it must have something to do with a specific speed. I've done a physics problem before asking at what speed the wheel looks reversed, but I can't do it.

Due to the visual residue of the human eye.

It is a visual misunderstanding, and this phenomenon is called poor beating.

When the frame rate of the picture is higher than 10 to 12 frames per second, the eye will not be able to distinguish between a still image and a moving image, and will think that it is a coherent movement. Movies are 24 frames per second, that is, 24 frames flash per second, while TV is 25 frames per second, in other words, every 0.00 seconds, the line of sight will be cut off by the switching of images.

In information theory, this phenomenon is actually a manifestation of "aliasing". When we sample a continuous signal at equal intervals, if the sampling theorem cannot or is not satisfied, the frequencies of the signal will overlap after sampling, i.e., the frequency of the front group that is higher than half of the sampling frequency will be rebuilt into a signal that is less than half of the sampling frequency.

The distortion caused by this overlap of the spectrum is called aliasing, and the reconstructed signal is called an aliasing double of the original signal because the two signals have the same sample value. The wonderful phenomenon that we see that the wheel does not rotate, or even turns backwards, is the aliasing caused by the overlap of the two signals sampled by the wheel and the camera.

When the rotational speed is higher than the visual frequency, the wheel turns forward; When the rotational speed is lower than the visual frequency, the wheel is spinning backwards. The phenomenon of visual persistence is a phenomenon in which the vision produced by light on the deficit retina is retained for a period of time after the light stops working, and its specific application is the shooting and projection of movies. The reason is caused by the speed of reaction of the optic nerve.

It is the basis for the formation and dissemination of animation, film and other visual **. Vision is actually imaged by the lens of the eye, and photoreceptor cells sense light, and convert light signals into nerve currents, which are transmitted back to the brain to cause human vision. The photoreceptor cells rely on some photoreceptor pigments, and the formation of photoreceptor pigments takes a certain amount of time, which forms the mechanism of visual suspension.

Main advantages: Visual temporary Bi elephants were first used by the Chinese, and the marquee lantern is the earliest visual temporary use according to historical records. In the Song Dynasty, there were already horse lanterns, which were called "horse riding lanterns" at that time

Then in 1828, the Frenchman Paul Rogue invented the photographic disc, which is a disc that is pinned through on both sides by a rope. A bird is drawn on one side of the plate, and an empty cage is drawn on the other. When the disc rotates, the bird appears in the cage, which proves that when the eye sees a series of images, it retains one image at a time.

It is a phenomenon of visual persistence. When the wheels are driving at high speed, the dots on the wheels are like people running on a circular playground, for example, at the starting point, and the image of the person's next reaction is after the starting point, but it has actually run nearly a lap, and it is like a person going backwards in a row. You can also do a simple experiment by drawing a distinct black dot on the disc to change the speed of the rotating disc, and you can see a change similar to clockwise and counterclockwise clockwise.

The phenomenon of visual persistence (persistence of vision, visual staying phenomenon, duration of vision), also known as the "afterglow effect", was first proposed by Peter Mark Roget, a professor at the University of London, in 1824 in his research report "The Visual Persistence Phenomenon of Moving Objects".

When the human eye observes the scene, the light signal is transmitted to the brain nerves, and it takes a short period of time to pass through the end of the light, and the visual image does not disappear immediately.