A trick with a tie

Son: Dad! I learned an awesome new trick at school in science class. Can I borrow your tie?

Dad: Let's see it.

Son: if we fold your tie in half, and roll the fat end toward the middle, and the thin end toward the middle, we have two rolls - one big and one small, both the same length, right?

Well, if I hold up the tie from the middle, and let go of both sides at the same time, which side will unroll first?

Dad: I have no idea.

Son (drops both ends, which open at the same time):

It's a tie, dad.