What happens to the density of a fluid when it is heated?

When a fluid is heated, its density decreases. This occurs because as the temperature of the fluid increases, the molecules within it gain energy and move more rapidly. This increased movement causes the molecules to spread farther apart, resulting in a larger volume of the fluid while maintaining the same mass. Since density is defined as mass divided by volume, an increase in volume with constant mass leads to a decrease in density. This principle applies to most fluids, including gases and liquids, facilitating convection processes where warmer, less dense fluid rises and cooler, denser fluid sinks. Understanding this relationship is crucial in fields such as meteorology and engineering, where convection plays a significant role in heat transfer.