Is hot water heavier than cold water?

Is hot water heavier than cold water?

Hot water is actually a little bit heavier than cold water because as Einstein told us E=mc2. So if E, the energy in the water, goes up because it’s hotter then mass, m, must also go up to keep the equation balanced [c, the speed of light in a vaccuum, doesn't change]. So there will be a very subtle and very tiny increase in mass of the hot water, compared to the cold water.

The reason the ice floats is actually because it’s a lot less dense than the water. The ice is made of water but it’s pushing a bigger volume of water out of the way, than the ice itself weighs. For that reason, it’s actually feeling a big push up from the water underneath it which makes it float, so that's the reason.