Everything around us is made up of matter. All solids, liquids and gases in the universe are matter. Matter takes up space and has mass, this means we can weigh matter. When we use one kind of matter to make something such as a wooden or plastic chair we say the material used was wood or plastic.
Materials are all around us. Some materials are solids, some are liquids and some are gases. A material will always be one of these three things. But what exactly are solids, liquids and gases?!
The word "property" has different meanings. We say this house is the property of Mr Mabusa (he is the owner of the house). When we use the word "property" in science we look at what makes that kind of matter special; how does it behave differently from other kinds of matter. For example when you shift a chair to another place, it will still have the same shape. This is because the chair is solid. So we can say that all solids keep their shape. We say that keeping its shape is a property of a solid. Let's look at some of the properties of solids.
So, we have learned that a substance in a solid form will have a fixed shape and takes up a definite space. Let's now look at liquids.
There are liquids all around you and you use them in your everyday lives. Some examples are water, paraffin, baby oil, fruit juice, petrol or methylated spirits. What are the common properties of liquids?
When a scientist wants to know more about something they set up questions and then they try to answer the questions by doing experiments.
After doing this activity where we investigated the properties of liquids, we can say that a liquid:
This is different to a solid. Remember a solid has a fixed shape and you cannot pour a solid!
When we breathe, we are taking in and giving out gases. But we cannot see the gas!
Gases are a bit more difficult to understand as we usually cannot see gases. We can see places where gases are used and the containers that a gas is kept in.
Can you name any gases? What about the gas used in a stove to cook food? Have you seen the gas coming out of the exhaust of a motor car? In hospitals, there are cylinders filled with oxygen gas for patients with breathing problems. The air you breathe in has oxygen gas. The air you breathe out has more carbon dioxide gas.
This is different to a solid. Remember a solid has a fixed shape and you cannot pour a solid!
We know that matter can be in the solid, liquid or gas state. Let's use water as an example.
So what have we learned from Mashadu's experience with the ice lollies? The ice lollies were frozen and cold. When they were placed in the sun, they started to warm up. This heat caused a state change to take place. The ice changed to a liquid. This is called melting.
When Mashadu and the Thunderbolt Kids went to get new ice lollies from the tuckshop, these ice lollies were frozen, but they were made from a liquid. The liquid was poured into the shape of an ice lolly and then they were cooled. As heat was removed, they froze. When a liquid changes to a solid, this is called solidifying.
Evaporation takes place when heat is added to the liquid. It means the water changes from the liquid to the gas state.
The steam that comes out of the kettle is extremely hot and you cannot see it. The steam quickly cools and forms tiny droplets in the air. These tiny droplets are visible and form the "cloud" that you see. When these tiny droplets hit the mirror they cool more and form the bigger droplets which you see forming on the mirror. We say the steam condensed to form water. The change of state from the gas state to the liquid state is called condensation, which takes place when heat is removed.
When you leave a glass filled with cold water on the table, small droplets form on the outside. This is because there is water vapour in the air which cools down when it is near the cold glass. The water vapour in the air around the glass condenses as it changes from a gas to a liquid and forms the tiny droplets you can see.
People say the Earth is the blue planet, because much of its surface is covered in water and the land forms a small part.
Did you know that the amount of water on Earth now is about the same as when the dinosaurs lived on our planet. How is that possible?
The answer is that invisible water vapour in the air cools and condenses to form drops of water. The reverse process takes place when water evaporates. When the water evaporates, it can not be seen anymore as it has become a gas called water vapour. This process of water always changing from a liquid to a gas and back again is an ongoing process. It is called the water cycle and this is why the amount of water on Earth stays the same.
In a cycle, a set of events (things that happen) keep on repeating in the same order.