Anyone think of a way to code string?

Not a string of text! Think of a man on the stage. In his hand is a string attached to a balloon flying above him.

When the man jumps the balloon goes up slower and so the string is relaxed a bit.

Anyone know how I would do this? I want it to be dynamic so he may be running, suddenly stop and the balloon would act appropriately.

I couldn’t even think of what to search for in Google…

Thanks to everyone who tries to help!