# 3. Using models to explain scientific ideas

The activities in this section will have begun to give the pupils some sense of what is called ‘the particulate nature of matter’. If you watch the way a sheet of paper cuts its way through the air as it falls, you can almost imagine the invisible particles getting in its way. Paulina mentioned particles when explaining the low pressure above the wing of an airplane.

It’s difficult to show pupils the particles in air – they are far too small to see even with a microscope, so we need to use models to help our pupils build a picture of what air is like. In the Key Activity, you use the pupils to be particles in the air. Many pupils enjoy learning by touching and doing, they enjoy being active and find it easier to remember what they have actually experienced.

In Case Study 3, one teacher builds a model to show how air is made up of a mixture of different particles and follows this up with investigations around breathing. Both types of approach give you the opportunity to assess your pupils’ learning.

## Case Study 3: A model for air

Mrs Mufaya really enjoyed science at high school, and she was enthusiastic about her pupils learning science in an active way.

Her class had been looking at air and talking about how it was made up of different gases and how people breathe in oxygen and breathe out carbon dioxide. Justina wanted to show that this isn’t right. You breathe in a mixture of gases and breathe out a mixture. It’s just that there is more oxygen in the air you breathe in and more carbon dioxide in the air you breathe out. How could she show this? The particles of each gas are invisible. To make it clearer, Mrs Mufaya demonstrated with a model.

She used everyday granular solids (salt, pepper, sugar, sand) to represent the separate parts of air and then very clearly mixed them together. She was then able to show that it wasn’t possible to just inhale oxygen. Rather, all the gases go into our lungs but only the oxygen moves into the bloodstream. (Resource 5: Finding out more about air gives more detail about Mrs Mufaya’s lesson plan.)

She followed this with two questions to her pupils:

• How many times do you breathe out in a minute?
• How much air do you breathe out in a normal breath?

She was delighted with their results. The class produced a lot of data. Together, they looked at the data and tried to answer questions such as: Who breathes faster, boys or girls? Older or younger pupils? and so on. They displayed their findings in charts on the wall using large sheets of newsprint.

## Key Activity: What is air?

First, squirt a small amount of an air freshener into the air in one corner of your classroom. Tell pupils to put up their hands when they can smell it.

Ask: How has it got to your nose? Guide their discussion to ideas of particles; air is made up of very small particles, which are moving round all the time.

• Now tell your class that they will be air particles.
• Take them outside to a suitable space.
• Tell them they must freeze when you call ‘stop’.
• Ask them to run around.
• After a minute call ‘stop’.
• Ask: Where are you all? How are you arranged?
• Select five pupils to stand near you and give them each a hat.
• Now ask everyone to resume running.
• Call ‘stop’ after a minute.
• Ask: Where are the pupils with the hats? Have they spread out?

Gather your pupils round you and talk about this model. Who were the pupils with the hats? How will they move if the gas is hotter? colder?

Take your class inside and ask them to use these ideas to work in groups to draw a poster to show how cooking smells spread through a house.

2. Exploring the properties of air

Resource 1: An introductory ‘air’ lesson