You’ll need
- 2 ceramic coffee mugs of the same height
- A ruler
- 5 tea light candles
- Sticky tape
- A small foil pie tin
- Half a cup of vegetable oil
- A teaspoon of glitter
- A spoon
- A box of matches
What to do
- Gather your materials on a flat surface.
- Place the coffee mugs upside down on the table, with a 5 cm gap between them.
- Stack the tea light candles on top of each other to create a candle tower. Your tower should be just shorter than the coffee mugs. You may need more or fewer candles depending on how tall your coffee mugs are.
- Tape the candles together to keep the tower steady.
- Place the candle tower in the 5 cm gap between the coffee mugs.
- Pour the oil into the pie tin.
- Add the glitter to the oil and stir it through.
- Place the pie tin on top of the coffee mugs, so that it sits between them.
- The bottom of the foil tin should be just above the top of the candle tower. Make sure that the pie tin is stable.
- Light the candle at the top of the candle tower.
- Watch what happens to the oil and glitter for 2 to 3 minutes.
Questions to ask
What causes the movement in the oil?
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 ziplock 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
When liquids and gases warm up, they rise above the cooler parts. In this activity, the oil that is closest to the candle flame gets warmer than the surrounding oil and rises. As the oil moves away from the flame, it cools and sinks. The glitter helps you see this pattern of movement.
The warm oil rises because it is less dense than the cooler surrounding oil. When something is dense, the molecules are packed tightly together. When it heats up, the molecules spread out and move around, making it less dense. Because the cool oil is denser than the hot oil surrounding it, the cool oil molecules sink. The hotter ones rise.
This flow of liquid of different temperatures is a convection current. There are big convection currents in the ocean. As cool water is less dense than warm water, cool water sinks to the bottom and the warm water rises to the top. Have you ever noticed this when swimming in a pool, river or ocean?
Convection currents deep in the ocean form when the cool water heats up. In some parts of the sea floor, heat from deep within Earth escapes through vents in Earth’s crust. This heats the cool water at the bottom of the ocean, causing it to rise. Cool water rushes in to fill the space left by the warm water. This cool water in turn gets heated and rises. As the hot water rises it cools down again, becomes denser and sinks, and the cycle continues.
Ocean currents help push water around the world, like a global conveyor belt. In fact, the system of ocean currents is actually known as the ‘global ocean conveyor belt’! This helps transport nutrients and sea animals around the oceans, just like in Finding Nemo. The water in the global conveyor belt moves very slowly, only a few centimetres every second.
Did you know
In the movie 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 ocean water is heated in the north where the climate is warmer closer to the equator. The EAC carries this warm water along the eastern coast of Australia down to the cooler waters in the south.
