Aside from the stabilizing tail of a bottle rocket, they physically don’t appear to differ much from a firecracker. They’re about the same size and appear to be constructed similarly, a short line of gunpowder wrapped in a cylindrical roll of paper. Yet they behave quite differently; one immediately explodes in place and the other shoots off into space due to a progressive ignition.
So what exactly is it that causes these two disparate reactions? Is it a different type of gunpowder? Is one vessel completely confined while the other is provided an escape point for the gasses? Is it the tightness of the wrap? I’ve wondered since I was a kid and no better place to ask…
[QUOTE=lieu;15411987 Is one vessel completely confined while the other is provided an escape point for the gasses? [/QUOTE]
Bing Bing Bing We have a winner! The hot gases have no way to expand in a firecracker, except by exploding the paper wrapper. In a bottlerocket (at least the propulsion stage), they gases can shoot out the open bottom.
And, the bottle rocket will usually include a secondary chamber with too small an entry for the gases to escape, so they explode once they’re up there.
Similar size and shape of charge, maybe, but the composition of a bottle rocket is more forceful. As a kid, it was a fun thing to do to crack open a firecracker and ignite the compound in a pile to a quick flash. If you try that with a bottle rocket, the flash is more of a light bang, even though it is no longer contained. I was pretty surprised, and the guys warned me, people have singed their fingers that way. It was serious, but apparently, not serious enough to warm me before I did it. Pre-teen boys are like that.
