How fast must an object be moving before it becomes imperceptible to humans?

Answer 1

Under ordinary circumstances (with air pressure), I don't think any large 3D object would be fast enough to be "imperceptible" if you're paying attention. Even if it goes past you fast enough to not be visible(mesured in angle per time relative to you, not absolute velocity, e.g. moon velocity example), you would notice the rush of air, or if it's much faster, a sonic boom that might damage your hearing, or much much faster, you'd be burned by the heat of the object (like a meteor in re-entry). So I think that's going to remain in the realm of comic book heroes, unless you're taking about A) in a vacuum like space, or B) an object with close to zero air resistance, like a sheet on edge, or C) Something going too fast to be seen but too small and slow to be heard, like a fast fly or a sleek bullet... ?

Answer 2

Objects can be moving thousands of miles per hour and you can still see them. The moon for example, orbits the earth at more than 2000 mph yet you can see it plainly. Its not just how fast an object is moving. Its how fast, how big it is and how close it is to you. Think of a jet airliner travelling at 600 mph. If it was passing you on the road it might be a blur but up in the sky a few miles away you see it clearly.

Answer 3

it depends on the size of the object

Answer 4

20 oscillations per second

Answer 5

It depends on its size, distance, and brightness!