Download printable Experiment Sheet here.
Convection is the process of heat transfer within a fluid. This fluid could be a gas such as in the atmosphere, water in the hydrosphere, or even molten rock in the geosphere! It is a very critical process four our dynamic Earth, and has a large role in driving how the four Earth systems interact.
If a point source of heat is applied unevenly to a fluid, the warmer fluid becomes less dense and rises, and begins to move to distribute the energy to the rest of the fluid. This is called advection, or the motion of hot fluid through colder fluid. This motion begins to mix the fluid and as the fluid moves, cold fluid moves to fill the volume of the hot fluid leaves behind.
Over time, this will result in a circular motion of fluid as hot fluid rises and cold fluid sinks. This process in large part is a driver of many of the air and ocean currents we see on Earth. Likewise the convection of rock in the deep Earth drives Earth's plate tectonic motions, as plates move and collide, providing the energy to create earthquakes, and make mountain ranges rise up.
Once the source of heat is removed or equalized, the advection will stop and heat will equalize through a process called diffusion. In diffusion, heat energy is shared by the water molecules in contact with each other without motion.
In this experiment, we can observe simple convection occurring in water on a stove top in boiling water.
Electric Kettle , Stove top or Hot Plate
- Fill kettle with water and bring to boil.
- Once boiling add a drop of food coloring. Note how the food coloring shows that the hottest areas of fluid are rising, and cooler areas are descending to fill the void.
- Observe what happens as the water cools.
Questions to consider:
- What is the temp of the food coloring at the beginning of the experiment compared to the water?
- Does heat tend to cause things to rise or fall?
- What happens when we turn off the heat? Or add food coloring to cold water only? If all the water is the same temperature will the water convect?
Examples of Convection on Earth
Thunderstorms and Air Currents