The reverse wheel rotation, an optical illusion?

in #stemng2 years ago (edited)

There are so many theories and so many sciences behind the very little things that happen even when we cannot explain them. This afternoon I got so inquisitive after finding it difficult to explain why something this awkward will happen. Let me tell you what this awkward thing is.

I was watching this movie on a satellite tv channel where a couple disagreed on something and one of them got pissed. He picked up the key to his car it was a 2006 Toyota Camry. And as he drove out of the compound everything looked normal till he got on the high way.

Something bizarre happened and even though I was not sure I tried to explain or find out what this thing that was tricking my eyes. Let me explain what it was as the man drove on the highway, everything looked normal and his car was moving in the right direction but as time went by, I began to notice his wheels. They looked like they stopped moving whereas the car was still moving past other cars comfortably which means the cars was still moving.

As time went by, I felt like I was losing my eyes or my mind as the wheels began to spin in the opposite direction but the other cars and the vegetation say otherwise as it was moving past them effortlessly. Then I decided to keep shut and not tell anyone of us watching the movie together because I hate going to the hospital, especially for treatment.

I picked up a mobile phone to check on the internet what could have happened to my eyes. It was then I discovered that this trick was not only been played on my eyes but on several people’s eyes. My instinct definitely told me there has to be something behind this strange thing that is happening right in our eyes. What this phenomenon or the science behind this is called the wheel wagon effect.





spinning, what do your eyes see?...image from pxhere from the public domain


The wheel wagon effect


The wheel wagon effect is considered to be a form of optical illusion, in fact, that would not be wrong considering the trickery these things play with my eyes. It could also be referred to as the stroboscopic effect, you would not be wrong to call it the stagecoach wheel effect it just depends on which one you can grab faster and easier.

The wheel wagons effect is not only noticed in the wheels of a car but in most rotational objects in movies but do you actually know why this happens?? The propeller of ships, the helicopter rotors, wheels of cars and carts.

The wheel wagon effect or stagecoach effect occurs in three stages just as I noticed earlier in my description where everything appeared to be moving normally and all of a sudden, the motion appeared to stop this stage. The last stage is the confusing part where the reverse rotation occurs, and all your eyes see is that the wheel is reversing but the motion is forward.

These are the stages of the wheel wagon effect and they would be discussed well in the next subtopic we are about to investigate.


What do your eyes really see?

see a video of the wheel wagon effect here.


If you were a game lover especially those who play FIFA or Pro evolution soccer on your system which can barely work with the capacity or specification of your computer system. Lol.
I know the struggle as I have been in such situation trying to manipulate the settings to the most compatible setting for such system one of such setting most of us do tamper with is the frame rate.

Why do I do such?

Sometimes when I start the game on my system I feel it is either too slow or most times I just feel my eyes are being pulled out as the movements of the players are either too fast or too slow for my eyes.
This doesn’t mean I have a kind of defect in my eyes or something? Of course, no! I have had several eye tests after and I was declared okay. This is what the frame rate does to one's eye.

Officially Wikipedia defines framerate as the frequency which consecutive or following images appear on display. Framerate is usually expressed in frequency per seconds (fps). source

This framerate is responsible for the way we see things either in videos or in real life. In fact, there are theories that our eyes see things just like the video camera.

Does this actually mean we haven’t been watching videos after all but pictures at a fast rate?

I remember taking some pictures using my android phone and I somehow wanted to turn them into a video, I had to download an app called android vid to mesh the pictures and guess what I had almost a straight video just as if I recorded it.

Now, let us imagine some sophisticated phones like Samsung whose camera has the feature of taking burst shots I mean multiple shots within seconds. I remember my phone could take up to forty in a blink of an eye. Well if such forty videos which were taken in a second and mesh together with microseconds as the time spacing in the application. We would get a perfect video.

So, yes! It is just like we have been seeing consecutive images in a very short period. This is what a video is, a compilation of pictures in swift motion.

The main thing we see or the problem is that the framerate of the camera used in recording those videos are lesser than the frequency produced by the wheels of the tyre.

It has been noted that most movie cameras operate at a frame rate of 24 every second so what really happens is that when the revolution or frequency is the same then what your eyes would interpret to your brain is a stationary movement whereas the tyres are moving so one might be confused.

Whenever this rotational frequency of the aircraft propeller, turbine vanes are rotating or tyre wheels are more than one begins to see the reverse movement because the camera is picking up the image at a negative degree which is interpreted to one's eye as a negative movement.

Although there might be cases where the wheels are decorated by spinners which revolve backward, in this case, your eyes see the right thing when taking a close look in the way the spinners rotate as the air acting on them turns them in any direction.


Summary

There have been many inquisitive moments as to why someone’s eyes at one point pick up a movement in a movie and it fades away slowly till one can only see the reverse rotation of the tyres. The sole reason is not due to our bad eyes but rather the cameras falling short of the frequency required to pick up the right speed.

So, the optical illusion that is being played on your eyes is actually not real although I still can't tell if some wheels are actually rotating or not if they do not have an environment to tell me what is going on.

Its something that is so annoying and stresses my mind out, perhaps in the near future better cameras used for recording great framerates would be produced and we can see better movements of tyres and machine parts on television.


References

Here are some of the books read for further knowledge:



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This is due to Nyquist–Shannon sampling theorem which says that you can reconstruct a signal only if you have twice the sampling rate. It's important in signal processing.
For example, in hi-fi audio you have a sampling rate of 44.1 kHz or above. This is to ensure that you can reconstruct 20 kHz which some humans can still hear, not me anymore :)
It is also the reason telephone sounds crappy. It is sampled at 8 kHz which means that it cuts all frequencies below 4 kHz. But it's a good trade-off for the bandwidth you get.
The same principle applies to the images captured by a camera.

Wow.. I have just learnt something. Thanks for this piece of information.

I came here to mention Nyquist-Shannon and see you've already handled it. As you mentioned, it applies to cameras, and is especially important in microscopy.

Interesting topic I must say. I do experience this in reality, I mean without viewing from a video playback. I think the eye as well has the frequency it can keep up with before it then begins to lag, as I have observed ceiling fans speed up, appear stationary and then reverse in direction.

Great post man.

It happens to your eyes?
Well i have not really focused on something moving.. I tend to take my eyes away before I start feeling dizzy but i can't take my eyes when it happens in movies.

I guess our eyes is almost like a camera.

This is so common.... Esp in movies where I get to see speeding tyres....

Thanks for this exposition!

Yea it is... Thanks for stopping by.

I've always noticed this phenomenon, but I never took out time to find out the reason behind it. About movies, remember they are called motion pictures...it is because motion pictures spliced together gives the feel of a motion. Same way flip book appear animated
flip book.gif

Yeah, the first time i saw this was a footage from a Lionel messi wonder goal versus Bilbao. The artist was good and he sketched the pictures well.

I guess that's what the movies do too they are just faster than the traditional scrolling

It's nice to learn about the wheel wagon effect. I usually observe that reverse movement in wheels but never had I sat down to think about it. I salute your good work, nice post.



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@adetola, it's a very nice post. I learnt a lot from it.
Thanks.

Thanks man

Wow, this post has answered a lot of questions.
I also used to wonder why the wheels appear like that.. Now i know

Hehehe.. Thanks bro

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