swim是动词，而swimming则是名词，表示游泳这项运动。swim，作及物动词时意为“游过；使浮起”，作不及物动词时意为“游泳；漂浮；浸；眩晕”。

第三人称单数：swims

现在分词：swimming

过去式：swam

过去分词：swum

swim是动词,只能做谓语

swimming可看成动名词,即名词,可作主语、be swimming作谓语,swimming还能做伴随状语

例如 he's thinking of something,swimming in the pool.

swimming还能做后置定语,修饰前面的名词

如bread is eaten by a fish swimming in the pool.

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。

She swam the 400 metres medley ten seconds slower than she did in 1980.她400米混合泳的成绩比其1980年慢了10秒。

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。