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Physics of Pyrotechnics
| Greater amounts of blackpowder/pyrex, when burned, produce more excess gases than do smaller amounts. These larger amounts of excess gases cause the shell to be pushed or propelled out of the mortar faster, resulting in greater initial velocities. The greater initial velocities produced by larger shells result in the shell attaining a greater height before it explodes and emits its bright flash of light. Shells usually travel about 100 feet vertically for every inch they are in diameter; depending on the angle they are fired from. |
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Pyrotechnics has always been a part of my other hobby, chemistry. It was not the only reason I was interested in chemistry - even today, the chemistry I am now happily doing really hasn't much to do with fireworks or pyrotechnic phenomena - but it provided an exciting field where to apply my newly acquired knowledge of chemistry.
For several years, my interest merely smouldered; it was not until I got my hands at real pyrotechnic literature that I wanted to learn the art properly. Since then, I have acquired a modest supply of chemicals, and a lot more skill in making stars, rockets and shells.
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The reactions we use must certainly be spontaneous, yet must not begin until the proper moment, even though all necessary ingredients are in close contact. This means that there must be some energy barrier to initiation of the reaction, which will not occur until this energy is supplied. This is only meant in a general sense; no such unique barrier can be identified. The agents will exhibit a range of sensitivity from the exquisitely sensitive that will be set off by the slightest shock, such as the decomposition of NCl3, to an almost total insensitivity, like that of TNT. In most cases, we search for a degree of sensitivity that will not respond to the usual shocks of handling and transport, but will detonate reliably when a definite stimulus is applied. |
The energy to start a reaction may be supplied by impact, friction, heat, flame, spark, radiation, shock wave or deformation. Each explosive agent has its own set of sensitivities to the various stimuli, so there is no single detonation energy that can be supplied by multiple means. The device supplying the initiating reaction is called the detonator, initiator, primer, first fire or some other descriptive name. The reaction in this device then initiates the main charge. A match is a simple example. The head of the match is the first fire, lighting by friction. Its heat then ignites the wood of the match, which represents the main charge. Often the "first fire" is not the initiator, but is ignited by it and strengthens its effect.
Nuclear explosions will not be included here, but they are precisely analgous to chemical explosions, in that the energy is liberated in a very short time interval by a very exothermic reaction. There are also mechanical "explosions" where the energy transfers occur in brief intervals. These, also, will not be included.
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