Why do liquid and gasses rise when heated?

When liquids and gases are heated, their molecules gain energy and move faster, causing them to spread apart and decrease in density. This decrease in density makes the heated liquid or gas lighter than the cooler surrounding fluid. As a result, the warmer, less dense fluid rises, while the cooler, denser fluid sinks, creating a convection current. This process is fundamental to many natural phenomena, such as weather patterns and ocean currents.