I was trying to read up on the mechanics behind an explosion in light of the tragedy in Beirut, but there’s a couple of things I’m not really understanding. I’m unsure of the concept of entropy and I’m unclear of the term shockwave if it applies to the visible portion of an explosion or the resulting blast followed afterwards. Any help is appreciated!
In: Physics
Entropy is concept usually taught senior year for physics majors. Understanding entropy is not really required to understand an explosion. All an explosion is, is an extremely rapid release of stored energy. In the case of ammonium nitrate, this energy comes from the nitrogen. Nitrogen’s lowest energy state is when it is bound to another Nitrogen atom. It really, really wants to return to this low energy state. So once enough energy is added to a system the nitrogen atoms to break their bonds with their current atoms and recombine with each other and release an incredible amount of energy in the process. Ammonium Nitrate by itself is not explosive, but when mixed with hydrocarbons (ANFO) or allowed to sit for a long period of time and decay, it will turn in into an extremely volatile nitrogen explosive.
A shockwave is just a wave of compressed air. The gases released during the explosion expand so quickly it compresses the air and rapidly increases the temperature. This increase in temperature, and the rapid cooling that occurs immediately afterwords is what causes the visible cloud to form in the shockwave’s path. The wave of compressed air travels outwards from the source in all directions and is the primary damage dealer in an explosion. Even in a nuclear blast it is the shockwave, not the heat and fire, that causes a vast majority of the damage.
When an explosive detonates, it creates a burst of supersonic hot gases (the actual fireball you see). These hot gasses push away the air around detonation, creating an expanding wall of pressurized supersonic air. This is a shockwave. The shockwave will continue traveling and expanding until it runs out of energy provided by the initial explosion. If you’ve ever felt a quick blast of compressed air, picture your entire body being hit with that, except several times more powerful.
Depending on the size of the initial blast, the shockwave can have enough energy to travel for miles, and damage property or even kill people (this is one thing movies continually get wrong, if you’re close enough to a blast to be thrown by the shockwave, you’re close enough for the shockwave to rupture your blood vessels and internal organs).
I don’t fully understand you answer, do you want to know what happens with the shockwave afterwards? that is simple to answer. the shockwave gets weaker over time, because of friction
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