One of the standard action
film clichés that
really bugs me is the scene in which the hero and the heroine are shown, in
slow motion, running away from an explosion.
Every time I see that, I think, "That is nonsense. An explosion expands much faster than anyone
can run." But of course I don't know that, so I just grumble a bit to
myself and go on watching. This morning,
during my regular four mile walk, I started thinking about this, for some
bizarre reason, so when I got home, I turned to Google. As always, Google did not disappoint. Here is a passage from a site I found,
at http://express.howstuffworks.com/explosion.htm.
"Can you really
outrun an explosion, like Sydney does every other week on "Alias"?
Let's go to the starting blocks: Sydney vs. chunk of C-4 explosive.
Let's go to the starting blocks: Sydney vs. chunk of C-4 explosive.
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Let's say
Sydney can sprint at about 15 miles per hour, or 22 feet per second. If we give
her a 10-foot head start to get to top speed, she'll be 32 feet away from the
center of the blast one second after the C-4 detonates. Not too shabby, but
it's not nearly fast enough. A C-4 explosion will expand at a rate of 26,400
feet per second. In other words, the blast is so fast it's almost
instantaneous. If she were in range of the explosion, she wouldn't have time to
think about running - or anything else. "
Never mind Alias, which I have never watched [so I
don't know whom Sydney is]. Isn't this
cool?
6 comments:
There is also an episode of Mythbusters where they tested this and, of course, came to the same conclusion.
I had never heard of Mythbusters, so I checked it out. very cool. Thanks for the info.
Yeah, they are big fans of C4 on that show. It's a little goofy sometimes, but on the whole a geeky pleasure.
Not so fast! Clearly the shock wave must be decelerating (I don't think dark energy is a factor here.) Thus, there must be a point at which a human being, running at a constant speed of 22 feet per second (say for 30 seconds) will be able to out run the blast. What is that distance from the point of explosion?
I think you would have to be so far away that you could not hear the explosion [since if the explosion is traveling at the speed of sound, that is way, way faster than anyone could run!] Obviously, if a bomb goes off in South Carolina, and I am here in North Carolina, I can, in some bizarre sense, outrun it, if I know to start running. But that is not what one sees in the movies. If Oppenheimer and the other physicists observing the first atomic bomb test had started running away from it as fast as they could run, even though they started several miles away, they still would not have outrun the bomb blast, for all that the blast was slowing down.
This post makes me sad because I can't help but thinking about all our soldiers coming hom with brain damage from IED explosions. They are going to need our help. I didn't vote for Bob Dole but I think he would handle this problem much better than "you're on your own" RMoney. Maybe Obama should talk about this problem a little. We'll be dealing with damaged minds and damaged souls for at least 50 years.
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