To do and notice Make a cup of hot water. Notice the shape of the colored region, it resembles a plume or a candle flame. Hold an ice cube about a centimeter over the card. Notice the color changes brought on by the downward flowing cold air. Air near the liquid is warmed by conduction, the warmer air rises transporting thermal energy to the card.
Air expands when it is warmed becoming less dense than the surrounding air and therefore buoyant.
Similarly, air falls when it is cooled. Convection occurs when thermal energy is transported from one place to another by the motion of a liquid or a gas. During a hot summer afternoon the warm ground heats the air, the air then rises forming large convective plumes called thermals. Soaring birds and glider pilots seek out thermals and enter them to be lifted to higher altitudes by the rising air. Convection also occurs within the tall towers of cumulus clouds.