Posts Tagged ‘Heat’

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.

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In the video below I show a great animation on convection currents in a room heated by a radiator that you can find on our website here. However, I don’t just give a tour of the animation, but I show how you can use it to encourage your students to talk about Physics in a creative way. It is a role play where you introduce the animation as a talk show of the life of the “Particles” family, which is your class. Well, the rest is in the video and I don’t want to spoil it for you, but I believe this approach is an interesting way to develop Communication and Literacy skills in your pupils in a fun way!

As always, I really value your feedback, so spend 10 seconds to leave a comment, please!

Here is a lovely classroom demonstration that I saw at the ASE Conference 2010 in Nottingham. The demo was part of the Physics Education Lecture, which displayed the best of the PhysEd magazine. I really learned a lot and was well impressed by the quality and creativity of the demonstrations, activities and workshops proposed by the Institute of Physics. As one of the IoP Network Coordinators I was very proud to be part of the Institute and see how many outstanding workshops and lectures they put together for the event. Apparently, the IoP did the majority of workshops and they were all free of charge, although the conference was organised by the ASE.

Anyway, coming back to our demonstration. At the lecture it was shown using two small glasses, so when I went back to my lab I thought; “What would happen, if I use two very tall columns of water? And this was the result!

Why don't the two liquids mix?

So, why won’t the two liquids mix?

I put cold water in the bottom column with some blue food colouring and boiling hot water in the top column with some red food colouring. The tricky bit is how to turn the top column upside down, as it is really hot and heavy, but it was well worth it! So, I put a sheet of paper on the top and then carefully turned it upside down (you might need a helper to do this). Then, I placed the top column on bottom one and as you can see, and unlike what the kids would expect, the red and blue water don’t mix. They actually stay unmixed for a very long time (over an hour at least).

But how do we explain such an effective phenomenon? Well, the hot water is less dense than the cold water at the bottom, as its particles have more kinetic energy, hence moving further apart from each other. The result is that we have two liquids of different density, with the less dense one at the top, which therefore will float on top of the denser cold water. It is a bit like having oil and water, you can tell your students!

This is a really nice demonstration that will really help your pupils to understand that hot liquid rises and cold liquid falls. It’s not only very memorable, but it also shows quite clearly that in heat convection currents it’s not the “heat” that rises, but the hot liquid, or gas.