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Convection Currents

two black upside down mugs on a white table cloth, with a silver cylinder between them, and a small aluminium dish sitting on the cylinder

Have you ever boiled rice or pasta and wondered why it rises and falls? Did you watch Finding Nemo and consider trying to catch a ride on the East Australian Current with all those cute, animated cartoon characters? Well, be prepared to be carried away by the currents that you'll create in this simple activity!

Australian Curriculum links

  • Science > Chemical Sciences > Year 3 > ACSSU046
  • Science > Physical Sciences > Year 3 > ACSSU049
  • Science > Earth and Space Sciences > Year 7 > ACSSU116
  • Science > Nature and Development of Science > Year 7 > ACSHE223
  • Science > Physical Sciences > Year 9 > ACSSU182

You'll need

  • 2 ceramic coffee mugs
  • ruler
  • 5 tea light candles
  • sticky tape
  • small aluminium pie tin
  • ½ cup of vegetable oil
  • 1 teaspoon of glitter
  • spoon
  • matches

Try this

Safety: This experiment requires adult supervision. Perform this experiment away from curtains or other flammable materials.

  1. Place the coffee mugs upside-down on a table, leaving a 5 cm gap between them.
  2. Stack the tea light candles on top of each other to create a candle tower. Your tower should be just shorter in height than the coffee mugs. (Please note: The number of candles required depends upon the height of your coffee mugs.)
  3. Tape the candles together to stabilise the candle tower.
  4. Place the candle tower in the 5 cm gap between the coffee mugs.
  5. Pour the oil into the pie tin.
  6. Place the glitter in the oil.
  7. Using the spoon, stir the oil to evenly distribute the glitter.
  8. Place the pie tin on top of the coffee mugs, with one edge of the pie tin on one coffee mug and the opposite edge of the pie tin on the other coffee mug. Ensure that the pie tin is stable before proceeding with steps 9 and 10.
  9. Use a match to light the candle at the top of the candle tower.
  10. Observe what happens to the oil and glitter for 2 to 3 minutes.

Further investigation

Try using a slightly bigger pie tin and use more candles under it. How do the extra heat sources change the movement of the oil?

Put a couple of ice cubes in a zip-lock bag. Place the bag in the oil at one edge of the pie tin. How does the ice change the movement of the oil? What could the bag of ice represent?

How could you represent islands or continents in your 'ocean of oil'? Test your ideas. How do they change the movement of the oil?

What's happening?

Glitter has been added to the oil to make it easier to observe the movement of the oil. The oil that is near the lit candle gets hot and rises. As the oil moves away from the lit candle, the oil cools and sinks.

The different areas of hot and cool oil in the pie tin cause the oil to flow. When the oil heats up, it becomes less dense and rises. The density of oil is a measure of how many oil molecules are in a given volume. Hot oil molecules have more energy than cool oil molecules. This means that hot oil molecules move around and spread out, making hot oil less dense than cooler oil. Because hot oil is less dense than the cooler oil surrounding it, the hot oil molecules rise.

As the hot oil moves away from the candle's flame, it cools down. Cool oil molecules have less energy than hot oil molecules. This means that cool oil molecules move less and take up less space, making cool oil denser than hot oil. Because the cool oil is denser than the hot oil surrounding it, the cool oil molecules sink.

This flow of fluid of different temperatures is called a 'convection current'. There are convection currents in the ocean. The ocean water is heated in areas where heat is escaping through the crust of the Earth, called hydrothermal vents. The less dense hot water rises. As the hot water rises it cools down, becomes denser and sinks. The cool water heats up again as it approaches the hydrothermal vent and rises and continues the cycle of rising and falling. This cycle is what creates the deep ocean currents.

The global conveyor belt is a collection of deep ocean currents. It is a massive flow of water that circles the globe, below the surface of the ocean. The water in the global conveyor belt moves very slowly, at only a few centimetres per second. The global conveyer belt is very complicated because the currents in the global conveyor belt are heated by a number of sources and the flow of the water is impacted by factors other than convection currents, such as differences in salinity.

Real world links

You may have seen the currents modelled in this experiment in the movie, Finding Nemo. In Finding Nemo, the main character, Nemo, rides the East Australian Current (EAC) from the north-east to the south-east coast of Australia. The EAC is an example of an ocean current that is created by the heating and cooling of water. The EAC carries warm water along the eastern coast of Australia from the warmer waters in the north to the cooler waters in the south.