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Movies and TV shows frequently show buildings being bombed, cars blowing up, etc. Frequently these are really explosions of miniatures filmed up close.

Aside from the speed that the explosion expands relative to the size of the object (which can be adjusted by slowing down the film), are there any features of an explosion that clue us in to the scale on which it occurs?

To be definite, let's imagine two tank trucks of gasoline, one 10m long and one 10cm long, but otherwise with the same proportions and made from the same materials. We film the big one exploding from 100m away and film the little one exploding from 1m away. How would we tell which footage is which?

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I think they may have done this on Mythbusters one time... can't remember details though. – David Z Apr 13 '11 at 6:23
up vote 4 down vote accepted

Note that by changing the overall scale by a factor k, you are changing the volume of the gasoline by k^3, and the area you are viewing by k^2. So the overall size of the explosion (ie visible flames etc) is not invariant. To find out what is k, you'd have to know lots of details about the fuel etc I suppose.

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not just that, but many materials behave differently depending on thickness, volume, etc. That smaller volume of gasoline may well burn much more completely and quickly than the larger volume in the full scale model, causing a hotter but shorter lived flame. And of course the small model will be made of different material, certainly much thinner material, which fragments differently. – jwenting Apr 13 '11 at 6:34

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