Some types of cherries do float and some do not.
For some cherries if they do float then they may be bad and then again there are some types of cherries that do float.
In my experience any cherries that I've had and eaten they never floated and always sank to the bottom of any drink I put them in.
However even if a cherry does float it still may be good.
Look inside the cherries because sometimes they may contain worms which are not harmful to humans to eat however they are not very appetizing that way.
Cherries are very good for your health and contain lots of vitamins, minerals and nutrients to keep your body healthy and energized.