Science Knowledge and Understanding

What is a scientist?

Describe what a scientist looks like. Then write what a scientist does. Underneath this, draw a picture of a scientist.


Scientists classify things

You need to know that scientists classify things to show that some things have similar properties.

 1. You will need to be able to classify things based on properties such as size, shape, texture, hardness, flexibility, strength, and colour.

[Ideas for writing explanations and getting students to think about the properties of different materials]

2. You will need to be able to classify things as natural or processed.

[Lesson Ideas for Teachers: Pipes and/or Supermarket Bags Activity]

3. You will need to be able to classify matter as either a solid, a liquid or a gas based on what you observe. You will also need to explain why some things are difficult to classify.

[Lesson Ideas for Teachers]


What is matter?

Matter is everything that you can see, touch/feel or smell (Fire, light and heat are not matter). Matter can be invisible or so small that you can’t see it.  Most matter can be classified as either a solid, a liquid or a gas.

Solids are usually hard. They can hold their own shape. They can be broken, cut, ripped, smashed, squashed, eroded, etc.

Liquids can be poured and easily change shape to match the shape of their container. They flow to form a flat surface and fill all the space at the bottom of the container. Solids that pour don’t form a flat surface, but make a low hill as the bits stack up on each other. 

[Is it a liquid? Procedure and Explanation]

[Sand pours! Is it a liquid? Procedure and Explanation]

Gases are mostly invisible. They flow or spread out in every direction to fill the entire container. The container needs to have a lid or the gas will escape. Like solids and liquids, all gases have weight. Some examples of gases are air, water vapour, helium and oxygen. Smoke, fog and smog are not coloured gases. These things are just air mixed with lots of small bits of solid.

 [Lesson Ideas for Teachers]

[How to prove that air is there: Procedure and Explanation]

[Gases are heavy: Procedure and Explanation]

[The Magic Towel Trick: Procedure and Explanation]

Solids, liquids and gases give us a simple way of classifying the state of matter. However, some things are difficult to classify this way. These things include hair gel, grease, mayonnaise, foam, and Oobleck (created from a mixture of corn starch and water).


Matter can change state. A change of state can be reversible.

Matter can change state with a change in temperature. These changes are often reversible. In other words, you can get back what you started with.


  • Heating some solids will melt them, turning them into a liquid.

  • Heating liquids will boil them, turning them into a gas.

  • Cooling liquids will freeze them, turning them into a solid.

  • Cooling gases will condense them, turning them into a liquid.

[Make water from thin air: Procedure and Explanation]

[Experiment: How quickly does ice melt?]

There are other types of reversible changes.

1. Dissolving solids

You can dissolve some solids in liquid. This change is reversible because we can get the solid back.  The solids dissolve, but they do not disappear. They just break into very, very small bits that become part of the liquid.  Using small bits helps solids dissolve faster. Stirring and heating also helps this happen.

Disolving solids in liquids is reversible because you can get the solid back by boiling the liquid or letting it evaporate. A good example is dissolving salt in water to make salty water. This change is reversible because when the water evaporates we are left with the salt that we started with.

Did you know that the salt you put on your dinner comes from the sea. The sea water is trapped and the water is left to evaporate. Once this has happened, the salt is cleaned and packaged. There is a company that does this in Corio Bay in Geelong.

It is important to understand that dissolving is not the same as melting.

2. Mixtures

Some mixtures can be separated by filtering the mixture. Dirty water is a good example. You can mix dirt with clean water to get dirty water. This change is reversible because we can filter the dirty water to make it clean again. The dirt gets collected in the filter. 

Be careful though: Some changes that you think are completely reversible may not be. For example, melted butter can be cooled so that it turns back into a solid, but it will not be the same as the butter that you started with. (And your mum will have to throw it in the bin. So don’t leave it out on a hot day!)



Irreversible Changes

Some changes to things are irreversible. With these changes, you cannot get back what you started with because you have made completely new materials. 


The signs of an irreversible change include a change in colour, bubbles, heat, a bright light, flames or an explosion. Some everyday examples include wood that has burnt and nails that have rusted.

It is important to know that some clever scientists can reverse some changes that we think are irreversible.


Science at Work

This term we are going to start working like scientists. You will need to:

  • watch demonstrations and ask questions;

  •  do experiments with your teacher and classmates to answer these questions;

  • plan, design and report on these experiments with the help of your teacher and classmates;

  • select and use simple measuring equipment when doing experiments;

  • draw and write what you observe from these experiments and comment on what you discover;

  • describe what a fair test is and say what things need to be kept the same when we are doing experiments so that the tests are fair; and

  • describe how to do experiments safely.


There are a number of suggested follow-up experiments for each demonstration that you could do as a class or in small groups. Click on ‘Experiments’ to find the following useful demonstrations that can be used:

  • Make a Film Canister Rocket

  • Fantastic Foamy Fountain

  • Make Your Own Rock Candy

  • Build a Fizz-Inflator

  • How to Make Slime – Method 1

  • How to Make Slime – Method 2

  • Make Plastic Milk

  • Build You Own Volcano

  • The Exploding Lunch Bag


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