Why does head hair constantly grow, arm hair and cat hair grow then stop?

As we all know, our head hair grows constantly so long as we're alive (and even seems to grow a little when we're dead, but that's just because the skin dries out), and without a haircut, as a baby grew to an adult, its hair could very well grow down to it's butt, or even to it's toes and it'd look like Cousin It. However, hair on every other part of our body, be it arms, knuckles, chest, armpits, pubes, or legs, seems to grow to a cirtain length, then stop. Meanwhile, on many animals the same thing seems to happen. If part of a cat is shaved for surgery or whatnot, it's hair will grow back to the length of the rest of it's hair (or in this case, fur), and no longer. Why does this happen? Why doesn't our hair stop growing after a cirtain length, and for that matter, why doesn't, for example, our arm hair grow indefinitely?

Why does head hair constantly grow, arm hair and cat hair grow then stop?

All hair has a set length at which it stops growing the follicle rests then drops the old hair and grows a new one.

The hair on our heads has a much longer set length than the hair elsewhere. Most folks have their hair cut long before it reaches the point of not growing any further.

Between the age of 20 and 32 I never had may hair cut. It stopped getting longer when it reached the small of my back.

There's a good bit of variation on what the set length for head hair is amongst people though. Same goes for beard hair as well.

Why does head hair constantly grow, arm hair and cat hair grow then stop?

All hair grows continuously. Arm hair and the like just shed with greater frequency.

Why does head hair constantly grow, arm hair and cat hair grow then stop?

All the hair on our bodies grows continuously. The hair on our head is obviously much denser, and the hairs are very seldom shed. The hairs on the remainder of our body (with the exception of the beard for men) are shed quite frequently, so they never have the chance to grow long.

Why does head hair constantly grow, arm hair and cat hair grow then stop?

hair grows .005mm a day. that is all i know. not to split hairs