My first plumbing problem

There's something strange going on with the tub in one of the bathrooms.

No hot water. Cold water comes out nice and strong like it's supposed to, but when I turn on the hot water, there's only a small dribble.

Hot water to the bathroom sink is fine. Hot water to every else in the house is fine. Just no hot water to the bath.

Not sure what's going on, but I guess I'll be learning a little bit about plumbing.