Final answer:
Hot fluids rise while cold fluids sink due to convection, where warmer material rises and colder material sinks. This happens because as the temperature of fluids increase, they expand and become less dense, causing them to rise.
Step-by-step explanation:
Hot fluids rise while cold fluids sink because of a phenomenon called convection. In convection, warmer material rises and colder material sinks, transferring energy. This happens because as the temperature of fluids increase, they expand and become less dense, causing them to rise. For example, when you heat soup, you may observe cells forming as the warm fluid rises to the top.