ballistics

n [sing v] study of things that are shot or fired through the air, eg bullets, missiles, etc 弹道学（对射击或发射之物如子弹、导弹等的研究）: [attrib 作定语] a ballistics expert 弹道学专家.

bale, baleful, balefully, balk, balk (also baulk), balky, ball, ball game, ball-bearing, ball-point, ball-point pen, ballad, ballade, ballast, ballboy, ballgirl, ballcock, ballerina, ballet, ballet-dancer, ballistic missile, ballocks, ballocks (also bollocks), balloon, balloon-borne, ballooning, balloonist, ballot, ballot-box, ballpark, ballroom, balls-up, bally, ballyhoo, balm, balmily, balminess, balmy, baloney, balsa, balsam,