Why we see an object motion blurred if it is fast enough? And why it seems like stopped if it is super fast, rims of a car or helicopter propeller for example?
In: Biology
(not a completely educated assumption below)
I dont have the complete answer… But it has to do with timing.
The rims on a car and helicopter can be replicated by the matching the frame rate of the filming with the speed of the rotation of the object.
I assume in real life its similar… Maybe out eye speed matches the speed of ye spinning object.
So your eyes work similar to a camera, light hits the receptor and creates an image. When things move really fast, the light gets to your eye before the image has enough exposure time, so you end up with a speed blur from where the light hit your eye before, and after the object had moved, making a blur.
I’m not sure if you’re asking about eyes or cameras. But I think the ‘cameras’ answer is interesting enough to share:
> Why we see an object motion blurred if it is fast enough?
Cameras cannot capture a single instant in time. If they did, the picture would be pitch black. A picture is created on the camera sensor as individual particles of light hit the camera over a *period of time*. This means you need to continuously expose the sensor in order to take a picture. The duration of this exposure is controlled by the camera shutter.
If the camera shutter is open for 1 second, and the object moves halfway across the camera’s field of view during that second, the resulting picture will show the object ‘smeared out’ over half the image.
You can reduce the amount of blur by making the period of time you leave your camera shutter open shorter and shorter. But if you make it too short, you eventually hit the limitation of there not being enough light particles to make a clear and crisp image.
> And why it seems like stopped if it is super fast, rims of a car or helicopter propeller for example?
Imagine a ball bouncing up and down, at a rate of once per second. If you take a photo at exactly 1 second intervals, the ball would appear to not be moving at all! (Apart from motion blur, which is still a thing)
The apparent ‘freezing’ happens because you happen to be taking pictures at *exactly* the points in time when the object appears identical to before.
The reason it happens so often for cars and helicopter propellors has more to do with the fact that they are rotationally symmetric, as well as them being fast *enough* to be faster than most picture rates used in video.
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