As the temperature of a fluid increases, what happens to its density?

As the temperature of a fluid increases, its density decreases. This occurs because heating a fluid generally causes its molecules to move faster and spread apart, leading to an increase in volume. Since density is defined as mass divided by volume, if the mass remains constant while the volume increases due to the increased molecular motion, the overall density of the fluid decreases. This principle is particularly important in understanding buoyancy and convection currents, as fluids with lower densities tend to rise, while those with higher densities sink.