Heat convection demonstration

Observe a beautiful demonstration of heat convection.
Can also be used to demonstrate the convection currents in the Sun.
Science content
Chemistry: Atoms, Molecules (3-7)
Physics: Heat (3)
  • large tub with clear sides (I use a 15L clear storage tub) - remove all labels
  • cold water, to fill the tub (from the cold tap is fine)
  • styrofoam cups
  • food dye - blue or darker colours work best
  • pipette or eye dropper
  • kettle, for boiling water
  • four tin cans, or supports, taller than a styrofoam cup

Set-up prior to experiment:
Stand a desk or table in an open area of the classroom. Arrange the four cans on the desk so that they can support the tub at each corner. Fill the large tub with cold water and stand it on the four cans so that it is stable. Wait for the water to become completely still before proceeding. Boil the kettle of water, so that it is quick to boil again. (Outdoors, hot water from a good quality thermos will work fine. Heat pads that get very hot also work, though not as well.)

Ask all the students to sit in a circle around the tub, so that they can see through the sides of the tub.
Suck up a little food dye into the pipette, then very slowly and carefully lower the pipette into the water and deposit a pool of food dye on the base of the tub. Slowly remove the pipette from the tub, so as to disturb the water as little as possible. (A second pool of food dye was used as a control in the photos above, but this is optional.)
Get the styrofoam cups ready - use one, or stack them, until they just slide under the tub.
Bring the kettle to the boil again, then immediately fill the a styrofoam cup (stack) with boiled water. Slide the cup(s) under the tub, and leave it directly below the pool of food dye.
After a few seconds, streams of food dye should start to flow upwards from the food dye (see last photo above).
Make sure all the students are able to see the food dye streaming upwards before continuing discussion. You may need to carefully wipe condensation from the outside of the tub for a clearer view.

The hot water in the styrofoam cup heats up the water and food dye directly above it, making the molecules here move faster as they gain heat energy. This group of fast moving molecules flow upwards in the water (because they are less dense than the surrounding cooler water). They take heat energy with them, and are moving by "convection". The visualized convection currents are beautiful as they trace out the curving patterns of heated water.
Convection is the movement of a group of higher-energy molecules through a liquid, or a gas. Convection is how heat moves around the air in the classroom.

For a lesson on the Sun, this demonstrates the convection currents that carry hot gas (not liquid) from the centre to the surface of the sun.
Diagram of section of the sun with convection zone:…
Each granule has a bright centre, which is the hot gas rising through a thermal column. The granules’ dark edges are the cool gas descending back down the column to the bottom of the convective zone. (From
Many, separate convection cells, form the granulation patterns on the surface of the sun.
Image of convection cells in the sun:
Video of granulations on the sun's surface:


This and other convection demonstrations at
Alternative set up: add an ice cube to the top of water. Drop food colouring on top of the ice cube. ?But then we see cold water sink, rather than warm water rise?
A thermometer dipped in should detect the difference between the warm water at the top and cooler water below. (From book Weather Watcher p.34, DK)
Coloured tablets (e.g. to put in the bath) do not dissolve fast enough to work.
Make convection cells with pearlescent shampoo in water in a tin plate on a hot plate.

Grades taught
Gr K
Gr 1
Gr 2
Gr 3
Gr 4
Gr 5
Gr 6
Gr 7