Ice floating and cooling the upper part of a drink should start a natural convection type cycle which cools the whole drink. If the ice sank, you’d have a very warm surface layer. Never thought about this with focus before 😅
2 points
Stones are less effective overall because they don’t melt. A very substantial part of the temperature change you get from putting ice in something is actually from thermal energy in the liquid going towards breaking the bonds between molecules that comprise solid ice in order to make it water. Without that sink for heat, you’ll still cool your drink by allowing the colder solid to absorb heat from the liquid, but the temperature change will not be nearly as much.
