What types of explosives do people use? How do explosions take place? How can explosions be beneficial?
David confronts the dangers of
explosives when he discovers
a ticking bomb in the Newton's
Apple Studio!
We often see the negative side of explosives on the news--images of twisted metal on damaged buildings or debris and rubble in a war zone. But explosives also help us construct tunnels, mine underground, remove obstacles during road construction, extinguish oil well fires, inflate automobile air bags, and destroy hazardous wastes.
An explosive is a stable material that, upon stimulation, very rapidly changes from a solid or liquid into a hot, expanding gas. The sudden release of energy and the accompanying pressure exerted on the surrounding materials by the expanding gas constitute an explosion. If you confined an explosive, you would increase the likelihood of the detonation by increasing the speed of the reaction. For example, when gunpowder is confined within the paper wrapping of a firecracker, it explodes when ignited. However, the same powder sprinkled in the open simply burns when ignited. In the confined state, the heat generated at the point of ignition will immediately ignite a large amount of surrounding material. The expanding gases from all the "burning" gun powder will act together, resulting in an explosion.
Explosives fall into two categories: detonating and propellant. Detonating explosives are further classified as initiating (primary) or secondary. Initiating explosives, the more sensitive of the two, must be handled with extreme care. They require only a low energy stimulus, such as being touched with a hot wire or tapped with a hammer, to explode. For that reason, they are put into blasting caps.
Secondary explosives are less sensitive and can burn without producing an explosion. They only detonate by means of a severe shock, delivered by another explosive (usually a blasting cap) placed in or near them. Since they are relatively stable, large amounts can be moved and handled safely.
The velocity at which explosives detonate determines their function. Explosives of low detonating velocity supply a slow push or heave. Explosives with a high detonating velocity have a bursting or shattering effect.
Propellant explosives are used for firearms, rockets, general engineering, and demolition work. They differ from detonating explosions in that an avenue of escape is provided for the expanding gases. For example, when the explosive propellant in the space shuttle solid rocket boosters is ignited, all the gases from the resulting continuous explosion escape out the bottom, providing upward thrust. Unlike a detonating explosive, not all the explosive material is burned at once in a propellant explosive.
Industries rely on small explosive charges for a number of purposes. In metallurgy, for example, metals can be pressed into dies, extruded, or welded together by means of such explosions. New metal alloys have been created that way.
a capsule containing a small amount of easily explosive
material used to explode more stable high explosives
Additional sources of information
Community resources
Explosives have different detonation velocities. Some shatter and others push. With water balloons, you will simulate the range of a blast.
Materials
How are explosives used for constructive purposes? In small groups, brainstorm the ways society benefits from explosives.
An explosion is considered anything that combusts with a spread of over 3,000 feet per second. Convert this rate to miles per hour. What other events occur at this speed?
Explosives have been around for a long time. Construct a time line to show the history of explosives from their invention to the present.
View some videos dealing with explosives. They could be World War II documentaries, footage of a shuttle launching, or motion pictures such as Hellfighters (about Red Adair's life). Write an account of the role of explosives in these videos.
From time to time, you will hear news of hydrogen gas, coal dust, grain dust, and even gasoline vapors that have exploded. What causes them to behave like an explosive? Research one of the above materials to determine its explosive characteristics and the conditions needed for explosions to occur.
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