today i learned – mon 27th feb 2017

we’re talking optical illusions today! #exciting 😬. have you ever noticed that when a car pulls off, the wheels look like they move normally but then at a certain speed they look like they’re moving backwards or not moving at all?

well in today’s #tdil, i’m going to tell you why that happens! well, try at least…i’m starting to worry that this blog is a bit like karl pilkington in word form. 

anyway, it’s called the ‘wagon wheel effect’ (omg wagon wheels with jam ❤️) and it’s all to do with frames per second (fps) and stuff. firstly, i think we should probably discuss that for a second! when talking about cameras, frames per second is defined as:

“a measurement for how many unique consecutive images a camera can handle each second”

in the mad wagon wheel effect, it’s exactly the same only with your eyes seeing images instead of a camera. so, if something can film at 30fps, then it captures 30 unique pictures (frames) every second.

your eyes are capable of operating at upwards of 200fps when processing light but not when detecting motion. in fact, when it comes to detecting changes in motion, your eyes can only operate up to 13fps.

despite your eyes operating at up to 13fps, your brain can only really compute 10-15 images per second (apparently, you can up that if you grab a nintendo and do lots of brain training).

right then, how does this translate to car wheels (and other things) going backwards or not moving? well, imagine a car wheel has four spokes in a cross shape (+) if the 12 ‘o’ clock spoke rolls slowly to 2 ‘o’ clock, your brain will be able to process it normally. this is because it catches the movement in multiple individual images (frames).

however, if the 12 ‘o’ clock spoke moves quickly through the positions before your brain processes the next frame, it’ll be tricked into thinking the wheel never moved <- this is why wheels/rotors/propellors/whatevs sometimes look like they aren’t moving.

however, if the 12 ‘o’ clock spoke manages to go all the way around to the 11 ‘o’ clock position before the next frame is processed by your brain, then the brain will determine the movement as the reverse of what it actually was (if a wheel is moving clockwise the brain will determine it as anti-clockwise) therefore, a wheel would look to you like it was going backwards.

this is why you get that transition between a wheel looking like it’s going forward and then backwards – your brain can process the movement normally until the wheel reaches a certain speed and frames per second.

it’s exactly the same principle when it comes to cameras 🎥 … if you film a wheel spinning and match the wheel’s spinning with the fps that the camera is filming at, it’ll look like it isn’t moving! (because the camera will only ever see it in one position, like in this video!)

and there you go! you’re now wiser than you were before you read this (possibly, you might have already known this or i may have made no sense) either way, you’re welcome 😬.

if you want to read more and see some examples, go –> here <– … although, if i’m honest, you’ve basically just read everything on there anyway!

tatty bye 🙂🙂 #tdil

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