Ry's Blog

Ben asked if there was anything we could learn from this:

While I was trying to go to sleep, I thought of something: the mass of the cardboard (that is, the resistance to acceleration) is enough to cause a very energetic gas of high volume to route around the constraint the mass provides. You can see some fringing along the top flap; I think this is the corrugation of the flap meeting the box edge. Light is escaping the corners and open edges, but the edges where the cardboard is folded are still holding.

We’ve wondered if the cardboard actually provides any extra “oomph” to the explosion; by confining it, it appears to allow the reaction to proceed at a higher pressure. This causes the reaction rate to increase, thus increasing the detonation velocity.

This is trivially provable; if you take a pile of explosives and put it on the ground, a detonation will cause a crater of some size. The same amount in a small tube will cause more damage on one axis and less on the other; if you lay it on the ground, it will cause less. If you stand it on end, it will cause more.

All of this is well known in the explosives community, but for me it was hard to buy that a small skin of inconsequential cardboard could really cause the extra “oomph”. For me, at least, this end the debate.