swim是动词,而swimming则是名词,表示游泳这项运动.
e.g.I usually swim a few laps as warm-up during practices.---我一般都会在训练中先游几圈作为热身.
My hobbies are painting and swimming.---我的兴趣是画画和游泳.
注：swim的现在进行时同样是swimming,不要把它和作为名词的swimming搞混了.
e.g.He is swimming right now.---她现在在游泳.