How does the density of a fluid change as it heats up?

When a fluid is heated, its density typically decreases. This happens because the molecules within the fluid gain kinetic energy as the temperature rises, causing them to move more rapidly and spread apart. As the molecules become more spaced out, the mass of the fluid remains constant while the volume increases, leading to a decrease in density.

This behavior is a fundamental characteristic of most fluids, especially liquids and gases, under normal conditions. As the density decreases with heating, the phenomenon plays a crucial role in convection. Warmer, less dense fluid rises while cooler, denser fluid sinks, creating convective currents that facilitate heat transfer.