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amendment
[edit]Canadian Islamic Congress' filing of human rights complaints against Islamophobic articles published on Maclean's magazine.
By contrast, American courts would not stop a planned march by the American Nazi Party in Skokie, Ill., in 1977, though a march would have been deeply distressing to the many Holocaust survivors there.
Six years later, a state court judge in New York dismissed a libel case brought by several Puerto Rican groups against a business executive who had called food stamps “basically a Puerto Rican program.”
In the United States, that debate has been settled. Under the First Amendment, newspapers and magazines can say what they like about minorities and religions — even false, provocative or hateful things — without legal consequence.
But racial segregation, second-class citizenship, racist terrorism (lynchings, cross-burnings, fire-bombings of churches) are living memories in the United States— they are no less vivid than the memories of McCarthyism that haunt the defenders of the First Amendment.
Explosion corresponds to rapid heat release or pressure rise. [1] A system could go from steady reactions to explosion, or vice versa. [2] Depending on the flammability limits of the gas mixtures (fuel and oxidizer) at given temperature and pressure, it is not necessarily that explosions result in combustion waves (fire). [3] Explosion is in itself a branched chain phenomenon. [4] What determines whether the [thermodynamic] system will explode or not is whether chain termination is faster or slower than chain branching. [5] From this analysis one concludes that if one radical is formed at a temperature in a prevailing system that could undergo branching and if this branching system includes at least one chain branching step and if no chain terminating steps prevent run away, then the system is prone to run away; that is, the system is likely to be explosive. Demonstrated by a kinetic model. [6]
thermal explosions. A thermal explosion occurs when a chemical system undergoes an exothermic reaction during which insufficient heat is removed from the system so that the reaction process becomes self-heating. [7]
Since the rate of reaction, and hence the rate of heat release, increases exponentially with temperature, the reaction rapidly runs away; that is, the system explodes. [7]
Astrophysical explosions result from the release of magnetic, gravitational or thermonuclear energy on dynamical time scales, typically the sound-crossing time for the system. These explosions include solar and stellar flares, eruptive phenomena in accretion discs, thermonuclear combustion on the surfaces of white dwarfs and neutron stars, violent magnetic reconnection in neutron stars, thermonuclear and gravitational collapse supernovae and cosmic gamma-ray bursts, each representing a different type and amount of energy release.[8]
2. Solar flares and flare stars 3. White dwarfs and neutron stars in binary star systems 4. Supernovae 5. Cosmic gamma-ray bursts
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An explosion is a rapid increase in volume and release of energy in an extreme manner, usually with the generation of high temperatures and the release of gases. Supersonic explosions created by high explosives are known as detonations and travel via supersonic shock waves. Subsonic explosions are created by low explosives through a slower burning process known as deflagration.
Causes
[edit]Natural
[edit]Explosions can occur in nature due to a large influx of energy. Most natural explosions arise from volcanic or stellar processes of various sorts. Explosive volcanic eruptions occur when magma rising from below has much dissolved gas in it; the reduction of pressure as the magma rises causes the gas to bubble out of solution, resulting in a rapid increase in volume. Explosions also occur as a result of impact events and in phenomena such as hydrothermal explosions (also due to volcanic processes). Explosions can also occur outside of Earth in the universe in events such as supernova. Explosions frequently occur during bushfires in eucalyptus forests where the volatile oils in the tree tops suddenly combust.[9]
Astronomical
[edit]Among the largest known explosions in the universe are supernovae, which results when a star explodes from the sudden starting or stopping of nuclear fusion gamma-ray bursts, whose nature is still in some dispute. Solar flares are an example of a common explosion on the Sun, and presumably on most other stars as well. The energy source for solar flare activity comes from the tangling of magnetic field lines resulting from the rotation of the Sun's conductive plasma. Another type of large astronomical explosion occurs when a very large meteoroid or an asteroid impacts the surface of another object, such as a planet.
Chemical
[edit]The most common artificial explosives are chemical explosives, usually involving a rapid and violent oxidation reaction that produces large amounts of hot gas. Gunpowder was the first explosive to be discovered and put to use. Other notable early developments in chemical explosive technology were Frederick Augustus Abel's development of nitrocellulose in 1865 and Alfred Nobel's invention of dynamite in 1866. Chemical explosions (both intentional and accidental) are often initiated by an electric spark or flame in the presence of Oxygen. Accidental explosions may occur in fuel tanks, rocket engines, etc.
Electrical and magnetic
[edit]A high current electrical fault can create an 'electrical explosion' by forming a high energy electrical arc which rapidly vaporizes metal and insulation material. This arc flash hazard is a danger to persons working on energized switchgear. Also, excessive magnetic pressure within an ultra-strong electromagnet can cause a magnetic explosion.
Mechanical and vapor
[edit]Strictly a physical process, as opposed to chemical or nuclear, e.g., the bursting of a sealed or partially sealed container under internal pressure is often referred to as an explosion. Examples include an overheated boiler or a simple tin can of beans tossed into a fire.
Boiling liquid expanding vapor explosions are one type of mechanical explosion that can occur when a vessel containing a pressurized liquid is ruptured, causing a rapid increase in volume as the liquid evaporates. Note that the contents of the container may cause a subsequent chemical explosion, the effects of which can be dramatically more serious, such as a propane tank in the midst of a fire. In such a case, to the effects of the mechanical explosion when the tank fails are added the effects from the explosion resulting from the released (initially liquid and then almost instantaneously gaseous) propane in the presence of an ignition source. For this reason, emergency workers often differentiate between the two events.
Nuclear
[edit]In addition to stellar nuclear explosions, a man-made nuclear weapon is a type of explosive weapon that derives its destructive force from nuclear fission or from a combination of fission and fusion. As a result, even a nuclear weapon with a small yield is significantly more powerful than the largest conventional explosives available, with a single weapon capable of completely destroying an entire city.
Properties of explosions
[edit]Force
[edit]Explosive force is released in a direction perpendicular to the surface of the explosive. If a grenade is in mid air during the explosion, the direction of the blast will be 360°. In contrast, in a shaped charge the explosive forces are focused to produce a greater local explosion, shaped charges are often used by military to breach doors or walls.
Velocity
[edit]The speed of the reaction is what distinguishes an explosive reaction from an ordinary combustion reaction. Unless the reaction occurs very rapidly, the thermally expanding gases will be moderately dissipated in the medium, with no large differential in pressure and there will be no explosion. As a wood fire burns in a fireplace, for example, there certainly is the evolution of heat and the formation of gases, but neither is liberated rapidly enough to build up a sudden substantial pressure differential and then cause an explosion. This can be likened to the difference between the energy discharge of a battery, which is slow, and that of a flash capacitor like that in a camera flash, which releases its energy all at once.
Evolution of heat
[edit]The generation of heat in large quantities accompanies most explosive chemical reactions. The exceptions are called entropic explosives and include organic peroxides such as acetone peroxide.[10] It is the rapid liberation of heat that causes the gaseous products of most explosive reactions to expand and generate high pressures. This rapid generation of high pressures of the released gas constitutes the explosion. The liberation of heat with insufficient rapidity will not cause an explosion. For example, although a unit mass of coal yields five times as much heat as a unit mass of nitroglycerin, the coal cannot be used as an explosive (except in the form of coal dust) because the rate at which it yields this heat is quite slow. In fact, a substance which burns less rapidly (i.e. slow combustion) may actually evolve more total heat than an explosive which detonates rapidly (i.e. fast combustion). In the former, slow combustion converts more of the internal energy (i.e. chemical potential) of the burning substance into heat released to the surroundings, while in the latter, fast combustion (i.e. detonation) instead converts more internal energy into work on the surroundings (i.e. less internal energy converted into heat); c.f. heat and work (thermodynamics) are equivalent forms of energy. See Heat of Combustion for a more thorough treatment of this topic.
When a chemical compound is formed from its constituents, heat may either be absorbed or released. The quantity of heat absorbed or given off during transformation is called the heat of formation. Heats of formations for solids and gases found in explosive reactions have been determined for a temperature of 25 °C and atmospheric pressure, and are normally given in units of kilojoules per gram-molecule. A positive value indicates that heat is absorbed during the formation of the compound from its elements; such a reaction is called an endothermic reaction. In explosive technology only materials that are exothermic—that have a net liberation of heat and have a negative heat of formation—are of interest. Reaction heat is measured under conditions either of constant pressure or constant volume. It is this heat of reaction that may be properly expressed as the "heat of explosion."
Initiation of reaction
[edit]A chemical explosive is a compound or mixture which, upon the application of heat or shock, decomposes or rearranges with extreme rapidity, yielding much gas and heat. Many substances not ordinarily classed as explosives may do one, or even two, of these things.
A reaction must be capable of being initiated by the application of shock, heat, or a catalyst (in the case of some explosive chemical reactions) to a small portion of the mass of the explosive material. A material in which the first three factors exist cannot be accepted as an explosive unless the reaction can be made to occur when needed.
Fragmentation
[edit]Fragmentation is the accumulation and projection of particles as the result of a high explosives detonation. Fragments could originate from: parts of a structure (such as glass, bits of structural material, or roofing material), revealed strata and/or various surface-level geologic features (such as loose rocks, soil, or sand), the casing surrounding the explosive, and/or any other loose miscellaneous items not vaporized by the shock wave from the explosion. High velocity, low angle fragments can travel hundreds or thousands of feet with enough energy to initiate other surrounding high explosive items, injure or kill personnel, and/or damage vehicles or structures.
Notable explosions
[edit]Chemical explosions
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Nuclear explosions
[edit]Use in war
[edit]- Artillery, mortars, and cannons
- Gunpowder and smokeless powder as a propellant in firearms and artillery
- Bombs
- Missiles, rockets, and torpedoes
- Atomic bombings of Hiroshima and Nagasaki
- Land mines, naval mines, and IEDs
- Satchel charges and sapping
- Hand grenades
Volcanic eruptions
[edit]- Santorini
- Krakatoa
- Mount St. Helens
- Mount Tambora
- Mount Pinatubo
- Toba catastrophe theory
- Yellowstone Caldera
Etymology
[edit]Classical Latin explōdere means "to hiss a bad actor off the stage", "to drive an actor off the stage by making noise", from ex- (“out”) + plaudere (“to clap; to applaud”). The modern meaning developed later:[11]
- Classical Latin: "to drive an actor off the stage by making noise" hence meaning "to drive out" or "to reject"
In English:
- Around 1538: "drive out or off by clapping" (originally theatrical)
- Around 1660: "drive out with violence and sudden noise"
- Around 1790: "go off with a loud noise"
- Around 1882: first use as "bursting with destructive force"
See also
[edit]
Definitions from Wiktionary
Quotations from Wikiquote
- Combustion
- Deflagration
- Detonation
- Dust explosion
- Explosion protection
- Explosive limit
- Fuel tank explosion
- Implosion (mechanical process): opposite of explosion
- Internal combustion engine
- Mushroom cloud
- Piston engine
- Plofkraak
- Standards for electrical equipment in potentially explosive environments
- Underwater explosion
Footnotes
[edit]- ^ Glassman & Yetter, p. 261.
- ^ Glassman & Yetter, p. 87.
- ^ Glassman & Yetter, p. 84.
- ^ Glassman & Yetter, p. 85.
- ^ Glassman & Yetter, p. 82.
- ^ Glassman & Yetter, p. 79.
- ^ a b Glassman & Yetter, p. 77.
- ^ Wheeler 2012, p. 774.
- ^ Kissane, Karen (2009-05-22). "Fire power equalled 1500 atomic bombs". The Age. Melbourne. Archived from the original on 2009-05-27.
- ^ Dubnikova, Faina; Kosloff, Ronnie; Almog, Joseph; Zeiri, Yehuda; Boese, Roland; Itzhaky, Harel; Alt, Aaron; Keinan, Ehud (2005-02-01). "Decomposition of Triacetone Triperoxide Is an Entropic Explosion". Journal of the American Chemical Society. 127 (4): 1146–1159. doi:10.1021/ja0464903. PMID 15669854.
- ^ wikt:explode#Etymology
References
[edit]- Keller, Jay O.; Gresho, Martin; Harris, A.; Tchouvelev, Andrei V. (December 2014). "What is an Explosion?" (PDF). International Journal of Hydrogen Energy. 39 (35): 20426–20433.
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- Lemkowitz, Saul M.; Pasman, Hans J. (2014). "A Review of the Fire and Explosion Hazards of Particulates". KONA Powder and Particle Journal (31): 53–81. Archived from the original on 2020-02-05.
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- Glassman, Irvin; Yetter, Richard A. (25 August 2008). Combustion (4 ed.). Elsevier. ISBN 9780080568812.
- Wheeler, J. Craig (13 February 2012). "Astrophysical explosions: from solar flares to cosmic gamma-ray bursts". Philosophical Transactions of the Royal Society A. 370 (1960): 774–799.
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