Everything you can see around you is matter. It is built up from atoms into bigger and more complex units, such as molecules (collections of atoms), and the cells that make up living things. There are even smaller bits of matter inside atoms, such as protons and neutrons - and there are even smaller bits of matter inside those.
We think of the Earth as land (solid) with air (gas) and oceans (liquid) drifting around us, and space as mostly emptiness with stars and planets dotted around. In fact, only a tiny amount of the Universe is ordinary matter - most is contained in two mysterious forms called dark matter and dark energy.
Unlike matter that we can see around us, dark matter is invisible. We can only tell it is there from the effect it has on ordinary matter. Astronomers first suggested dark matter as a way of explaining why some stars and galaxies seem to have less mass than expected.
The theory of dark energy was suggested to explain why the Universe is expanding faster than expected. It is believed to be a force that is fighting gravity and making the Universe expand rapidly. Although there is evidence of this, not all scientists are convinced dark energy exists.
Everything around us is either matter or energy. Every day we use thousands of different materials. We can define all these things as either living or nonliving matter. Although both are built from atoms, they work in different ways. Living matter constantly renews itself, while nonliving matter only changes when things around it force it to change.
Living matter: Living things grow and change by absorbing energy and matter from the environment. They are powered by sunlight, which enables plants to grow, providing food for animals too.
Nonliving matter: Earth is mostly rock, containing dozens of chemical elements that people have used in many ways. Nonliving matter is the power behind everyday products and inventions.
Energy: Albert Einstein discovered that tiny amounts of matter can be turned into vast quantities of energy. This process powers the Sun, producing the light energy that supports life on Earth.
All matter on Earth is built from about 100 different elements, each of which is made up of atoms. Atoms can join together to form larger structures called molecules. Compounds are substances formed when atoms from different elements combine. We can understand almost everything on Earth by inspecting what it’s made of.
Living things are ever changing, while nonliving things always seem the same - there are rocks on Earth that are hundreds of millions of years old. When living things die, they can turn into other living things (such as dead leaves that fertilize the tree they fell from). Often, living things are reborn as nonliving ones. Oil forms under the sea when dead microscopic plants decay over millions of years.
Types of change
There is always a scientific logic behind the changes that occur in our world. We can understand this by looking at the living or nonliving things present before and after a change, and seeing whether there was a physical, chemical, or biological change.
Physical changes: When ice changes to water or steam, it is still the same substance, but a physical change occurs.
Chemical changes: Fusing hydrogen and oxygen gases forms water, changing the original substances.
Biological changes: Plants convert water into new growth. In this change, the original substance disappears.
Everyday decisions often involve comparing one material to another. You might eat eggs for breakfast instead of toast, because they fill you up more. That is a choice between two materials based on how much energy each one contains. Depending on the weather, you might wear a thick wool sweater or a thin cotton shirt. That is a choice of materials based on their physical properties - how well they insulate your body heat. When you wash, you might use a bar of soap or a shower gel. That is a third choice based on chemical properties - how well they break down dirt.
Properties of Materials
Every material is good for some things and bad for others because of its properties (how it behaves). The physical properties of a material include how strong or hard it is, how easy it is to work into shape, and how it is affected by heat, electricity, and light. A material’s chemical properties include the ways in which it changes when it comes into contact with substances such as acid or water.