Use the convection demonstration video with Lesson 14: Steps 1-2, How and Why Does Air Move in the Tropics, of the GLOBE Weather curriculum.
This video shows convection happening as a model to partially explain the movement of air around the Earth. The cup below the center of the clear tub contains hot water, which is warming the water inside the tub above it. A drop of red food coloring on the bottom of the tub helps us to see what happens to the water as it warms. The warmed water rises and cold water, with blue food coloring, moves slowly along the bottom, towards the center of the tub.