You'll need

  • A 10 cm piece of cheap plastic twine. It might also be called poly string. You can get it from supermarkets, hardware stores or office supply stores
  • Sticky tape
  • A stick. This can be a real stick, or a ruler, spatula or skewer
  • Scissors
  • Hot water
  • Cold water or an open fridge

What to do


Scissors are sharp. Be careful using them. Be aware of dangerous heat sources and don’t use materials that might get too hot. Ask an adult to handle hot or boiling water. Don’t use your heat octopus over open fires or other extremely hot surfaces. Supervision is recommended for young experimenters.

Moving air will interfere with your heat octopus. It works best indoors with air conditioners and heaters turned off.

  1. Take your 10 cm piece of plastic twine and tape one end of it to one end of the stick.
  2. Tease apart the other end of the twine into thin strands. This will be your heat octopus. The thinner and lighter the strands of twine, the better your heat octopus will be.
  3. Try holding the heat octopus over some hot water so the arms dangle just above and see what happens. Try and hold it as still as possible or rest it on something stable. You should see the arms start to move around.
  4. Now hold your heat octopus over cold water. Can you see a difference?

Questions to ask

Can you make your heat octopus move faster or slower? Try holding your heat octopus to the side of a heat source and watch what happens.

What's happening

Hot air rises in a process called convection. Air that is heated becomes less dense than colder air. For example, a litre of warm air weighs less than a litre of cold air. This means warm air floats on cold air, so warm air rises. Cold air then flows in at the bottom, filling up the space left by the rising warm air. In your experiment, the hot air pulls the thin strands of twine along with it as it rises. This lets you see convection happening!

Convection happens outside as well. The Sun heats up air particles, which rise up and spread out. This results in areas where there are not as many air particles in a given space. This is called an area of lower air pressure. The cooler air around the warm air will rush in to fill the gaps, creating wind. Convection is what causes winds to blow around Earth. Convection is also responsible for the most powerful storms, especially cyclones and hurricanes that form over warm ocean waters.

Did you know

Have you ever thought about how the Sun sustains Earth? Almost all living things on Earth, including us, get energy from the Sun. The Sun’s light and heat travel approximately 150 million kilometres to reach us. This energy powers life-sustaining processes and systems, such as photosynthesis and the water cycle. We can’t survive without the Sun.