Implosion
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Template:Otheruses4 Image:Nuclear weapon implosion.gif Implosion is a process in which objects are destroyed by collapsing in on themselves. The opposite of explosion, implosion concentrates matter and energy. Buildings are colloquially, though mistakenly, described to implode when demolished through explosives, causing them to collapse on themselves. Another example of implosion is a submarine being crushed from the outside by the high pressure of the surrounding water, because of a leak.
In an implosion-type nuclear weapon, a sphere of plutonium, uranium, or other material may be imploded by spherical explosive charges, increasing the density by a factor 2 to 3, making the mass critical, resulting in a nuclear explosion. In a fusion bomb, this in turn triggers nuclear fusion. These spherical high explosive charges form a spherical assembly of multiple high explosive charges. When a spherical assembly of multiple high explosive charges is used this is called a segmented design.
In the context of cavitation, implosion is a suctional process that causes matter to move inwards, not outwards as is the case with explosion. This inward (centripetal) motion, however, does not follow a straight (radial) path to the centre; it follows a spiralling, whirling path. This is called a vortex. In cavitation, a number of small bubbles of water vapor are created by the low pressure on one side of a propellor. When these bubbles collapse they can produce intense local shock waves which create noise and can cause local failure at the propellor's surface, a process leading to material erosion.
A characteristic feature of a vortex is that the outside of the vortex moves slowly and the centre moves fast. As water is imploded in a vortex, suspended particles, which are denser than water, are sucked into the centre of flow, frictional resistance is reduced and the speed of the flow is increased.
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