Implosion (mechanical process)

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Implosion is the collapse of an object into itself from a pressure differential or gravitational force. The opposite of explosion (which expands the volume), implosion reduces the volume occupied and concentrates matter and energy. Implosion involves a difference between internal (lower) and external (higher) pressure, or inward and outward forces, that is so large that the structure collapses inward into itself, or into the space it occupied if it is not a completely solid object.^{[citation needed]} Examples of implosion include a submarine being crushed by hydrostatic pressure^[1] and the collapse of a star under its own gravitational pressure.

In some but not all cases, an implosion propels material outward, for example due to the force of inward falling material rebounding, or peripheral material being ejected as the inner parts collapse. If the object was previously solid, then implosion usually requires it to take on a more dense form—in effect to be more concentrated, compressed, or converted into a denser material.