Archive for May, 2014

So we’ve seen it in every Die Hard and James Bond movie, in most action flicks and, of course, in Star Wars (but I’m referring to Tomb Raider because, hey, I really like the games). And, of course, we love it: at some point there’s a huge explosion and the hero either outruns it or even uses its power to reach some other previously out-of-grasp location. We are pretty sure that using a explosion for transportation does not sound really healthy, but … is it possible to outrun a explosion?

starwars

Basically, any explosion consists of releasing a large amount of energy in a small space really fast. This is usually achieved by burning explosive material. This process releases a large amount of concentrated gas that immediately fills the space around and pushes the surrounding air. Think, for example, of a small firecracker. If you make it explode on your OPEN hand, at most you’ll get some burning. If you close it, you’d better learn to tie your shoes singlehanded.

The power of the explosion, of course, depends on the material. For example, we would need 320000 large grenades (aprox) to equal the force of the explosion at Chernobyl and yet the largest nuclear device ever tested was approximately 100000 times stronger (50 megatons).

The material also has influence on how fast the explosion spreads: it depends on which gas combination is released. For example, in a C4 explosion gases are released at (approx) 8000 m/s (17900 mph). A really fast race car can reach 220 mph (around 350 Km/h), while the fastest (puny) humans can do 100 m in around 10 seconds. If no other factors are considered, a really fast guy could outrun a C4 explosion in a second if he was at least 7990 meters away from its center when he started to run and he accelerated from 0 to 10 m/s instantly. You get the idea.

This is not exactly true, because (depending on the material) a blast does not usually last that long -typically some milliseconds- and the area of influence of the expanding gas is not infinite either. Whatever. In any case, given the numbers above, the only way to outrun a explosion is basically to be out of its range from the very beginning, which, depending on the explosive, may range from a few hundred meters to a few kilometers (we are not going nuclear here, obviously). Still, it looks great on screen.

More information in How Stuff Works

Note: This entry covers the explosion, not the deflagration (the wall of fire that are associated to explosions in the movies to make them look cooler) which are waaaaay slower

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