bobbin, bobbing

Bobbin or bobbin means a reel or spool for thread, yarn, or wire--
The sewing machine has a spool of thread on top, and a bobbin underneath.
The machine is working fine, but the bobbin is empty.

Bobbing or bobbing is a form of "bob", meaning to move up and down; to walk or move with an up-and-down motion--
He walked to the music, bobbing his head as he went.
The children want to try bobbing for apples.

Now that you know that, you can say--
"If you wind the bobbin too fast, you'll see it bobbing up and down."

Note--"bobbin' ", with an apostrophe at the end, is a way of trying to write colloquial speech, meaning "bobbing"--
"When the red, red, robin comes bob, bob, bobbin' along..."