とまらない in One Punch Man OP meaning とまれない (negative potential)

Question

The negative form of 止{と}まる (to stop) is 止まらない, and the negative potential form is 止まれない.

However, I've noticed that 止まらない can be used in the sense of 止まれない. For example, the OP for One Punch Man goes like this:

ONE PUNCH!

(Three! Two! One! Kill shot!)

参{さん}上{じょう}！　必{ひっ}勝{しょう}！　至{し}上{じょう} 最{さい}強{きょう}!

なんだってんだ？　フラストレーション　俺{おれ}は止まらない (meaning: Nobody can stop me)

http://www.lyrical-nonsense.com/lyrics/jam-project/the-hero-ikareru-kobushi-ni-hi-wo-tsukero/#page=Japanese

Other examples:

2. "Help! I can't stop!" = 「助{たす}けて。止まらない。」http://japanese.about.com/blpod021101.htm

3. The song 涙{なみだ}が止まらない放{ほう}課{か}後{ご} is translated as "Unstoppable Tears After School". Wouldn't "Unstoppable Tears" mean 涙が止まれない? https://en.wikipedia.org/wiki/Namida_ga_Tomaranai_H%C5%8Dkago

Why is this so? Are there other verbs that behave like this?

Answer 1

Well, it appears to me that you're confused with the transitivity of 止まる. While the English word "stop" is used both transitively (as in "I stopped the taxi.") and intransitively (as in "Then the taxi stopped."), 止まる is always intransitive. The transitive version is 止める, and its potential form is 止められる.

So 俺は止まらない just means "I don't stop" or "I will never stop." The translation in the linked site, "Nobody can stop me," is a kind of free translation.

And 「助けて、止まらない」 means "Help! This [car/horse/machine/etc] won't stop!", not "I can't stop [something]!" (I don't think English speakers usually say "This car can't stop!" either, but correct me if I'm wrong)

涙が止まらない is a natural way to say "tears keep falling down", but 涙が止まれない sounds very unnatural, because tears don't have their own will and they don't move or stop actively. (私が)涙を止められない makes sense.