First motion definitions

first motion

The first indication of motion of a vehicle from its launcher. Synonymous with takeoff for vertically launched rockets and missiles.
Found on http://www.daviddarling.info/encyclopedia/F/first_motion.html

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first motion

first motion. On a seismogram, the direction of ground motion as the P wave arrives at the seismometer. Upward ground motion indicates an expansion in the source region; downward motion indicates a contraction.
Found on http://www.encyclo.co.uk/local/21456

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