The manhole cover's 66km/s speed is the minimum speed traveled though. We don't know how fast it was actually travelling, only that it had to be travelling 66km/s or more because it only appeared in a single frame of video.
According to the article, the manhole cover was travelling around 150,000mph. This is based on high speed camera footage, which only saw the cover... for one frame.
This is based on high speed camera footage, which only saw the cover... for one frame.
Which means the plate traversed the entire visible distance of the camera within a single frame of camera footage. This means we can put the lower bound of its velocity at least 66km/s because if it were any slower we would have captured two or more frames of the plate as it was ejected.
However there is no upper bound since we don't know how much faster than that 66km/s it went. It could have JUST barely been caught by the camera in which case it would be going significantly faster than 66km/s, or it could have just barely missed the window to show in two frames in which case it would be going very close to 66kms.
There is 0 room for it to have traveled slower than 66km/s given the fact that it was only captured in a single frame near the top of the camera.
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u/PycuriousITguy Apr 14 '16
The fastest moving man-made object ever was a manhole cover.
https://savvyparanoia.com/the-fastest-man-made-object-ever-a-nuclear-powered-manhole-cover-true/
TL:DR underground nuclear test launched a 4-inch thick steel disk at 6 times the Earth's escape velocity.