Why hot water rises and cold water sinks?

Question

During the descent of the submarine once a submarine starts sinking; it will always sink to the bottom of the ocean if no other changes are made.

Answer 1

Any object or substance that is less dense than a fluid will float in that fluid, so hot water rises (floats) in colder water. When fluids are cooled, they contract and therefore become more dense. Any object or substance that is more dense than a fluid will sink in that fluid, so cold water sinks in warmer water.