Section 3

Looking at liquids

Introduction

Learning Outcomes

By the end of this section, you will have:
  • used ‘big picture’ mind maps to see what pupils already know when starting a new topic;
  • undertaken practical classroom demonstrations to challenge pupils’ thinking;
  • planned different sorts of activities including investigations and drama to develop pupils’ understanding of the role of water.

Whatever age you work with, it is always valuable to start a new topic with a thoughtful session where you build up a good picture of what the pupils already know. This can be recorded in the form of a mind map (see Key Resource: Using mind maps and brainstorming to explore ideas). Encourage pupils to share any questions and concerns they have. Knowing your pupils’ learning needs will really help you plan in a meaningful way. What sort of things must be planned? (See Key Resource: Planning and preparing your lessons.) In this section we guide you through using a mind map and planning a series of activities around liquids and their properties.

Page 1

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.

Page 2

Some people are predicting that future wars will be fought over water – an alarming thought. Water is our most precious resource. How do we ensure that pupils appreciate water and value using it wisely? The amount of water found on Earth is about 1,400 million million litres. Most of it is found in three places:
    • oceans and seas (97%);
    • frozen, as ice (2%);
    • underground (1%).
There is also some water in lakes and rivers, in the atmosphere and in living things. Case Study 2 shows an interesting way of combining science and language in a drama activity about water supply. It is important to use a range of different types of activity in science as each pupil will have a preferred learning style – some will learn best through doing, some through seeing and some pupils will be happiest listening. In Activity 2, you plan and carry out a demonstration that shows how to extract clean drinking water from salt water or dirty water. As with all demonstrations, we suggest you try this out before the lesson and think carefully about the questions you will ask the pupils during the demonstration.

Case Study 2: Thank you for a drink of water

Kholiswa Somyo integrates her pupils’ learning whenever possible. With ‘water’ she linked science to language by making a ‘big book’ with her class. She prepared everything carefully beforehand so that the combined lesson ran smoothly. She started by involving one of the shyer pupils and developed a little classroom drama. She got Sipho to come to the front and said to him: ‘Nantsi ikomityi yamanzi.’ (Here is a cup of water for you.) Of course, the polite boy said: ‘eNkosi M’am, for the drink of water.’ To which, she surprisingly replied: ‘Don’t thank me! I only gave you the water. Thank the … ’ (and she pointed to the ikomityi). So Sipho thanked the cup. ‘Don’t thank me,’ said the cup, ‘I only held the water. Thank the … ‘(‘Tap!’ a few children in the class said). ‘That’s right,’ said Kholiswa and got Thembinkosi to come and be the tap. So Sipho went to thank the tap. ‘Don’t thank me,’ said the tap (Thembinkosi), ‘I only poured the water. Thank the … ’ (‘Pipes!’ called out many pupils). And so the lesson went on, building up the story of the local water supply, but in reverse; pipes, reservoir, pump-house, and so on. (Read a more detailed description of this lesson with advice in Resource 4: Making a big book.)

Activity 2: Getting clean water

It is possible to make clean drinking water from dirty or salt water. Ask your pupils: How can we do this? Listen to everyone’s ideas and note them down on the wall or chalkboard. Show your pupils how you can make salty dirty water drinkable. Heat a small quantity of water in a suitable container. Above the container place a piece of glass at an angle leading to another container. When the water boils it will turn to steam. The steam will condense on the piece of glass and drip into the second container. Explain these steps to your pupils. You will need to do this several times and put the important words on the board. Ask the class to look at the new water and describe it. What is left in the first container? This process is called distillation. Now ask your pupils to work in groups to do a design for a large-scale version of this experiment. How could they get enough clean water for their home? Ask them to present their ideas and as a class discuss the different proposals. (See Resource 1 for ideas.)

Page 3

For the final part of this section, we build on the ideas in the first two sections to ask pupils to solve the problem in the Key Activity (read this now). This activity uses investigative skills – predicting, planning, recording and presenting findings. Does this kind of activity keep your pupils interested? Can you think of other topics in the science curriculum where you could use this? Share your ideas with your colleagues. Perhaps you could start a journal of investigations in your school. Often, in science, the unexpected happens. In Case Study 2, one teacher uses a demonstration to challenge his pupils’ thinking – he shows that a metal needle floats. How is that explained? This type of activity gives you an opportunity to assess pupils’ understanding and to add to your original class mind map.

Case Study 3: A needle floats – exploring surface tension

Barnabas Ngcume had always been delighted by surprises as a child. In his science teaching he enjoyed finding unexpected ways to demonstrate the facts found in textbooks. This short demonstration certainly surprised his pupils and made them think carefully about the nature of water. He gathered together an open glass bowl, two-thirds full of water, a few ordinary steel sewing needles, scissors and a double-ply sheet of toilet paper/tissue. First, he asked the pupils to predict what would happen if you placed a needle on the surface of the water. They were all confident that it would sink. Barnabas let one of them try it – their prediction was right. Next, he took another needle and cut a small rectangle of tissue slightly longer than the needle and about 2 cm wide. He peeled apart the two layers and rested the needle on one of the rectangles. Carefully he lay both on the water. ‘See! It floats,’ he told his class. They all said he was cheating. But then, as they watched, the tissue became waterlogged and sank, leaving the needle floating on the thin skin of the surface. Barnabas didn’t give any explanation. He asked his pupils to discuss their thinking and questions in small groups. Then he asked them to suggest explanations for what they had observed and he shared some ideas about surface tension. At the end of the lesson, some of his pupils added the new information to their original mind map about water. (Resource 5: Surface tension gives background information for you, the teacher.)

Key Activity: What is the best way to dry a cloth?

  • Organise your pupils into groups of four.
  • Give each group a piece of cloth or paper towel to wet and then cut up. Now ask them to think of the best way to dry the pieces of cloth. Should the cloth be crumpled up? Folded up? Spread out? In the sun? In the shade? In a draught?
  • Each group should make a prediction and plan their experiment. What equipment will they need? What will they measure? How will they present their results?
  • Discuss with your pupils the need to keep everything the same except the one thing they are investigating – here, this is their method of drying. So they will need to make sure that each piece of cloth is the same size and have the same amount of water on it at the start.
  • When groups have their plan and their equipment, let them try their investigation.
  • Each group should present their findings to the class; they should include the best way to dry the cloth and things that went wrong in their investigation.

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