What is the most unexpected thing to break the sound barrier?

This question came up on Quora, and got a few interesting answers. I like this one, from a Dan Cohen.

In 1957 the US conducted a series of nuclear tests, called operation plumb-bob. During the test 29 nuclear explosions were conducted.

During the test one especially interesting event happened. The US wanted to test what would happen if they detonated a nuke underground. To test it they drilled a long hole deep underground. Lowered a nuke inside very carefully and covered the nuke under several meters of concrete. And placed a manhole cover over the hole so nothing would fall inside. Similar to this one:



Although it was presumably a bit larger. For the test they positioned a high speed camera to capture the test filming at 1000 frames per second. Which I find very impressive they had considering it was 1957, before Sputnik was launched.

This was the first US underground nuclear explosion; as such they had no idea what to expect.

Anyway, they detonated the bomb as planned. However the camera caught something very interesting. In a single frame of the video the camera caught the manhole cover. By calculating the distance the manhole traveled in the time it did they could calculate the minimum speed it traveled. This is exactly what they did. And one of the researchers on the project calculated the minimum speed it traveled at was 6x the Earth's escape velocity. Or 200,000 kph! Or 162x the speed of sound! Depending on how you measure it that would make the manhole cover the third fastest or the fastest human-made object ever.

The reason it was so fast is that when the bomb exploded it vaporized the concrete which in turned expanded pushing the manhole cover. Or in other words the bomb turned the entire hole into a large gun barrel.

There is a bit of a debate if it made it to space, as some say it would have burned up by the atmosphere on its way to space, while others say it was so fast it didn't have time to burn up.

If it did it would be one of the first human-made objects to make it to space, with only the German V2 rocket beating it.

I would link the video but it was never declassified.

richard09 wrote:

Although it was presumably a bit larger.

Yes, the steel bore cap was 2,000 pounds, and welded to the shaft opening. A minority of scientists think it shot into the atmosphere.  The wider opinion is that it simply vaporized in the explosion, like almost everything else around a nuclear detonation.  There simply isn't enough structural integrity to survive acceleration from zero to 150,000 mph in 1/1000 of a second.

One more comment, a personal one from me.  The very first nuclear explosion held the possibility, discounted but not ruled out, of igniting the atmosphere.  These underground detonations held dangers of their own, ranging from opening up cracks in the crustal plates to earthquakes to disturbing oil & natural gas deposits to permanently embedding radioactivity underground.  It seems to me that these scientists were extraordinarily careless.

Just vaporizing isn't nearly as amusing. I want to vote with the minority.

The idea of setting the atmosphere on fire sounds far-fetched, although I have heard it mentioned before. The idea of doing serious damage underground is much easier to believe, especially these days. We now know much more about fault lines and earthquakes, and have seen how many deep faults exist in areas that we thought we already understood. I don't know that cracking a crustal plate is a live possibility, but rearranging the countryside for miles around the blast looks very real, maybe even likely.