## Electricity and Heat

Our final classes in this term exploring The Physical World.

We switched the activities around because I was waiting for a delivery of electrical components but both groups covered basically the same stuff.

# Heat

The children love playing the ‘solid-liquid-gas’ game where they pretend to be particles that move around more depending on how much they are heated up. We have done this since we first covered materials science and they often ask to play the game even if it does not relate to our current topic! Each time I introduce the game, I explain how they have to stand together in a fixed position to be a solid, start to jiggle around as the solid heats up, move around a bit more but stay near to each other for liquids, and run around in straight lines as gas particles. It translates the concepts into physical activity, and is wonderful for kinaesthetic learners, although I have to be careful to specify how much space the gas takes up, otherwise we have stray particles that disappear out of visual or aural range! We practice solid, liquid and gas a bit and then I shout out ‘melt’, ‘freeze’, ‘evaporate’ etc. and the children stand in position or move around accordingly.  It also provides an opportunity to talk about sublimation, a less well-known phase transition directly between solid and gas, e.g. for carbon dioxide (dry ice) or iodine.

We had a discussion about heat sources and the children drew different heat sources on pieces of paper, e.g. the Earth’s core, the Sun, a hairdryer and even a phoenix (we didn’t discriminate against fantastical sources).

The solid-liquid-gas game was a great introduction to talking about conduction, and then other methods of heat transfer. We modelled conduction in a solid. The children stood in a line and I told them there was a heat source (like a fire or a hairdryer) at one end. The child closest to the heat source started to wobble, then the child next to them, and so on, like a Mexican wave. (It probably helped that they had done similar activities at the start of the term for transverse and longitudinal waves.) We didn’t really model convection or radiation but we talked about them and then went to look at a worksheet of different situations where heat is being transferred. (I don’t expect the children in my classes to do much reading or writing but we do have worksheets occasionally.)

# Electricity

There is very little about electricity in the NSW primary syllabus. Children in Stage 3 (Years 5 and 6) are expected to understand about sources of electricity and how scientific knowledge can inform the decisions that we need to make about methods of electricity generation and the impact these have on the environment. We covered this part of the syllabus by playing Energy Trumps (pdf) (from the Centre for Alternative Technology in the UK) and, outside of class time, I recommended that children try the Electrocity game online.

In the class I set up various simple DC (direct current) electrical circuits and provided the children with circuit diagrams and a key to the symbols used. The children enjoyed identifying which circuit was which, quickly identified the ones which would not work (due to an incomplete circuit or lack of a power supply) and went on to create their own circuits with simple components.

There is no substitute for letting children actually work hands-on with scientific equipment. I think I am not exaggerating to say that every child enjoyed this class and could have carried on for longer. Maybe another year we will make simple devices for them to take home with them.

## The Material World class 2: more gases, and properties of materials

Our second class about The Material World went very well. Everyone was attentive and came up with great ideas about the topic.

The younger group (roughly KS1 or ages 5-7) repeated several of the activities from last week, to introduce ideas of different states of matter, and to reinforce these ideas for those who had already learned about them. They seemed to all have plenty of fun running around being gas particles.

I then introduced a few other activities to get them to think about gases and their properties: blowing bubbles, blowing up balloons and using a home-made balance to show that a blown up balloon does weigh more than an empty balloon. The exhaled air is not ‘nothing’ or ‘weightless’ as children often think. One of the children provided a great answer to why we don’t feel the pressure of air pressing down on us – we are used to it!

We talked about all matter being made up of particles. I arranged some ping pong balls on a metal grating in a regular pattern, and used a borrowed hairdryer to blow them around on two different speeds. This was based on an exhibit in the Science Museum in London which I always thought was a great way to show the kinetic theory of gases. Our hairdryer couldn’t get the balls moving at great speed so I also showed them a video a friend of mine had taken of the actual exhibit.

With the older group (KS2 or 8-10) I went through the same or similar activities, and then moved on to considering the properties of different materials.

– How can we tell that an object is one material and not another, for example plastic instead of wood, or metal?

– What different properties do they have that make them appropriate or not for certain uses?

The boys closed their eyes and tried to guess what some objects were and what they were made of. I think if I do this again I will prepare some more fun objects with very different textures, densities and other properties. I might have to raid my little girl’s ‘treasure basket’ for these.

We wrote a list of different properties of materials which included colour, transparency, strength, electrical conductivity and thermal conductivity. The children were very good at coming up with ideas.

We had a great time testing materials for magnetism and for electrical conductivity. I was surprised to see that our Sydney tap-water conducts electricity pretty well even without anything else added, although our buzzer circuit was louder once we poured in some vinegar.

The boys then started designing some objects and deciding what materials to use them for and why. I asked them to design one sensible version and one silly version. They will continue with this next week, which will give us more opportunity to discuss how designers choose the most appropriate material for their objects. We will then move on to using magnifying glasses to look at the structure of different materials.

As I said earlier, I was very pleased with this week’s class and I feel the groups are working well.