1. Exploring prior knowledge through brainstorming and demonstrations
Because water is so important on Earth, we make it the emphasis when pupils learn about liquids. Case Study 1 tells how one teacher recorded pupils’ ideas about water on a mind map that would be added to throughout the topic. Could you use mind maps as a starting point for this topic? After making a mind map, or using another way to find out pupils’ understanding, practical demonstrations are important. These reinforce ideas and show how things work or happen.
In Activity 1 you undertake just one of the many possible teacher demonstrations that can be useful to show the properties of water – a waterwheel.
From ancient times people realised the power of flowing water. If water could be channelled to flow over or under the blades of a wheel, it makes the wheel spin. This can be used to drive other machines that do work like grinding meal or even generating electricity. If you do not have access to sufficient water for this demonstration, we suggest you try another demonstration such as ‘How would you show there is water vapour in the air in the desert?’ (Resource 1: Surviving in the desert outlines this activity.)
Case Study 1: Building the big picture and raising questions
Afua in Winneba, Ghana, always starts a new topic in a relaxed way, by gathering her Grade 4 pupils around her. She sits on a low stool, with a large blank paper on an improvised trestle behind her. She discusses the topic informally – in this case ‘water’.
Afua asks pupils what they know about water. She encourages them to listen carefully to each other and add to each other’s comments. She does not treat any idea as ‘wrong’ but asks the class to think about it before adding the idea to the mind map, and discussing where it will go.
She ensures there is a sense of logic to the mind map. When Dora mentions ‘floods’, all agree water can be dangerous, and the word gets written with other examples of dangers. When pollution and dissolved poisons get discussed, these too are linked to ‘dangers’. Later, they copy into their science notebooks the improved neater version Afua has made. While they do this they think about any gaps in their knowledge. Any questions are added to the mind map in a different colour. (See Resource 2: Sample mind map.)
Activity 1: Practical classroom demonstrations – waterwheels
This demonstration shows the power of flowing water to pupils in a dramatic, but simple way.Resource 3: Instructions for making a waterwheel shows you how modelling clay/prestik wrapped around a tube can hold blades of cardboard to represent a simple waterwheel. If the tube is free to revolve around a rod (axle) and a weighted string is fastened to the tube, then water poured over the blades will wind the string around the spinning tube and lift the weight.
We suggest you try this out before showing it to your pupils. Plan the questions you will ask them. These might include:
- Where have you seen this?
- What is the waterwheel doing?
- Where might this be useful?
You could extend the demonstration by finding out if altering the axle or the angle of the blades makes the wheel turn faster.
This demonstration integrates science and technology. When you stop pouring the water, there is a problem. The string will unwind. For technology, pupils might enjoy designing something to prevent the unwinding or using this device to do a job of work.