What is the slowest possible motion that a human can perceive as a moving object ?

 

 

In what time scale? And with just the naked eye or with the aid of technology?

 

With the naked eye, if I look at the clouds today, then they do not seem to move. But if I look for 15 seconds, and I take a stationary referencepoint (like a tall building), then I can see that they move. In some cases I only observe movement in 24 hrs, or even a week. I just have to come back and see if something changed.

 

Using more precise technology, we can measure that the leaning tower of Pisa actually moves by just a few centimeters per year (or millimeters per year?). We can measure that the continents move by a few cm per year. And with more precise technology we can surely measure even slower movements.

 

The longer you wait, the more obvious movement becomes. And the better the technology available, the better your measurements. I think you have to set some limits to the time scale... because I think (not sure) that we can argue that with infinite time, you can observe all motions, however slow.

This is a hypothetical . If an object moved 1 mm per 3600 seconds and if a person said they could see it move with the unaided eye over any few seconds of observation taken in this time interval , I would suppose this is extremely unlikely . Where does the speed start to get plausible ? 1mm/10min ? , 1mm/2min ? , 1mm/30sec ? , 1mm/5sec ? , etc