This article is from the Star Trek Tech FAQ, by Joshua Bell inexorabletash@hotmail.com with numerous contributions by others.
Warp travel is non-Newtonian. Without a constant influx of energy, the
subspace field will decay, and the ship will drop out of warp. In
other words, you *must* continue to provide energy to maintain your
warp velocity.
Anything which travels at FTL speeds must use a warp field (or some
other technology) to keep moving at those speeds.
 
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