I first saw the demonstration in the video below done by Clare Thomson at the “Best of PhysEd” lecture at the ASE Conference in 2010. Ever since I tried to make various versions of it, from using two very tall gas columns, filming it with high frame rate cameras, etc. But today I think I have made a really interesting variation of this really nice demo. The video below was made this morning in my kitchen.

Recreating this demo is very simple and I strongly recommend you do it with your classes, because the colours in the video don’t really reflect what you can see with your naked eye. I used water beads that I previously immersed in water containing blue food colouring for the cold water beads and red food colouring for the hot water beads. You will need to leave them in dyed water for about 8 hours. Then, I put cold water in the glass with blue beads and boiling water in the glass with red beads. When you mix cold and hot water with the cold water at the top, the red bead (much hotter) will rush upwards and the blue beads (much colder) will fall downwards. As the two types of beads swap places you have a nice simulation of what happens to the particles from hot and cold water, i.e. with more or less kinetic energy, when they mix. You have a very visual representation of a convection current forming in the two glasses. There is a limitation though, in fact, you can see that after a while the red beads begin to fall and collect at the bottom on top of the blue beads, but this is still quite effective at making the point that they have swapped places.

  1. Gary says:

    That may well be the best thing you ever did!! You need to write that up for Phys Ed. Awesome!

    • Alessio Bernardelli says:

      Thanks Gary,
      I thought it was quite clever 😉 Thanks for the comment. I can write about it on Phys Ed. it’s just a shame that paper doesn’t support videos yet 🙂

  2. Audrey says:

    Wow, this is a wonderful demo of convection! Where can you get the water beads? Thanks!

  3. Audrey says:

    Thanks! Will try this demo!

    • James says:

      Magic – what a great idea.

      If you get the coloured ones for this I’d suggest getting some clear ones at the same time as they ‘disappear’ in water and provide a version of the test tube in glycerol experiment without needing much extra.

      I’ve got my beads in the past for the refraction stuff from these folks
      I make no claims about them as a company other than the fact that I have orderd twice and that they arrived quickly and worked a treat.

  4. IanH says:

    This is similar to one of my demos, pinched from ‘Nina and the Neurons’ of all places! I use hot water with red food colouring, and cold water with blue. You use two versions set up, one with the hot water above and one with cold. Only one mixes immediately to get purple.

    • Alessio Bernardelli says:

      Yes, that’s the first version I saw at the ASE Conference from Clare Thomson and I love doing the warm water on top, as they don’t mix. Being able to see the beads moving adds some more sparkles to the demo I thought and it makes particle movement a bit more real to the learners minds.

  5. […] demonstrate heat transfer in fluids using the two chimneys apparatus and a convection square, plus hot and cold water with food colouring in gas jars, which I first saw in ‘Nina and the Neurons’. By the third demo the kids can predict […]

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