How fast do you need travel to leave an after image?

Answer 1

Well, you have to move much faster than 200 mph to be faster than the human eyes.

LeClairity shared this bit of info a while ago:

The question really is - can you move fast enough so that the eye won't perceive you. So, you don't have to move faster than the speed of light as some contributors suggest here - only fast enough so that you're moving faster than the eye's response time.

Think about a movie - the frames are about 24 frames per second, and you can't perceive the flickering. That is for no perception of flicker - the perception limit is maybe around 100-300 Hz depending on person and conditions. So, maybe around a few millisec.

So, lets say you are staring straight ahead, and a 0.25 meter wide person runs past. If they can move that 0.25 meter in 1 millisec, then they will effectively be "invisible". Or about 250 m/s. Then, by the time your eye catches up, the person has moved aready, so there is no overlap.

and


1 mile = 1609.344 meters
1 hour = 3600 seconds

First we find out how many meters per hour:

(250 meters / 1 second) * (3600 seconds / 3600 seconds)
900,000 meters seconds / 3600 seconds^2
900,000 meters / 3600 seconds
900,000 meters / 1 hour

Convert our total meters into miles:

900,000 meters * (1 mile / 1609.344 meters) = 559.235 miles

Therefore 250 meters/sec = 559.235 miles/hour

so if something moved at 559.235 miles/hour, or faster, it would be faster than your eye can perceive unless they saw it coming to or from, like a vehicle on a road or in the air.

but a Person would be a flicker or less.. The main problem is that Mach 1 is 760 mph and something moving that fast causes a physical atmospheric disturbance. A loud one

Answer 2

To leave an afterimage, an object must move faster than your eye can track. This varies individually, but typically around 60 mph is required to create a noticeable afterimage. The speed needed also depends on factors like distance traveled during the exposure time.