= Bound orbit
An <orbit> that remains within a bounded spatial region for all times for which the motion is defined. In an attractive inverse-distance <central potential> with zero <potential energy> at infinity, a noncolliding <orbit> is bound when its total <mechanical energy> is negative. That sign test depends on the potential and its energy origin; it is not a universal definition of bounded motion. A <closed orbit> repeats its position and velocity, whereas a general <bound orbit> can precess without closing.
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