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Comment by delinka | Hacker News Reader

Holy Hell. That second video really drives home the devastation caused in the blast wave. Paint on vehicles turned instantly to ash and blew away. Wooden structures instantly caught fire. What was unexpected to me (I saw this in the first video which made me aware of it) was the 'backwash' after the initial shock wave.

Terrifying.

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If you haven't seen a lot of atomic blasts, look up Trinity and Beyond. It's a documentary about nuclear warhead development and testing, with a lot of historical footage of the blasts themselves. In fact, I think the clip you reacted to is from that documentary.

Anyway, the damage you're seeing isn't actually typical for a nuclear blast. It's an effect called the precursor wind, and is in fact one of the distinctive things tested by shot Grable.

    A precursor is a very strong dynamic wind caused by the
    shell’s oblique angle of approach, and its high   
    horizontal speed. The nuclear explosion essentially 
    inherits the shell’s forward momentum, which sweeps 
    across the landscape causing extensive drag damage in 
    addition to the typical destruction. For instance, a jeep 
    which had been left virtually untouched by the much more 
    powerful Encore device was completely torn apart by the 
    artillery blast, and thrown a distance of about 500 feet.

http://www.damninteresting.com/atomic-annie-and-her-nuclear-...

I grew up in the 1960s and we lived within about 30 miles of 10 Titan II silos. They showed us these films constantly in school. With commentary. I can remember taking a map and using a compass to draw out the overlapping blast circles for a class project.

I highly recommend The Making of the Atomic Bomb. It goes into incredible detail about the blasts. One of the later chapters, using the example of hiroshima, discusses the effect of the blasts on the human body -- often to excruciating detail.

Your comment about the paint instantly turning to ash and blowing away made me think of the book. At a certain distance from the bomb, the wave isn't strong enough to instantly kill you, but much like paint on a car, you're skin will instantly blister from the heat, and then be blown off by the shock wave.

Horrifying stuff, but a really, really interesting read.

The prompt X-rays from the physics package heat up a lot of air very quickly. This expands, producing the supersonic shockwave front.

Then the fireball, being very hot and much less dense than the air around it, rises. Air is sucked towards ground zero, producing the backwash, and the characteristic mushroom cloud of any very large explosion.

And the fireball created by the X-rays is, for a moment, hidden behind the shock wave. This makes a "double flash" which can be detected from orbit without even the need for a camera, just point a photodetector at the Earth's surface.

Bhangmeters are one kind of specialised photo detector used to detect nuclear explosions:

http://en.wikipedia.org/wiki/Bhangmeter

I'm pretty sure these were used in bunkers (at least in the UK) as well as satellites.

Actually that second video looked mostly fake. Some of the footage was in "The Day After".

Its real. Many movies have reused stock nuclear footage. I recognize that video. Also, the effects in it are typical of nuclear blasts.

Sorry if I wasn't clear. The video was a clear hack job, interspersing many different pieces of footage from different tests. It was designed to fool a 1950s crowd. Let's be better than that.

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