The def of matter is one of the first definitions students meet in science, and it is also one of the most useful: matter is anything that has mass and takes up space. That short sentence covers an enormous range, from the air you breathe to the chair you sit on, from a drop of water to a distant star. If you are searching for the def of matter for homework, revision, or simple curiosity, this guide explains the definition in plain English, with clear examples, states of matter, and the difference between matter, mass, and weight.
Matter matters because everything you can touch, see, or measure in the physical world is made of it, or is a form of it. Scientists use the idea of matter to organise chemistry, physics, and biology, and to explain how substances change, combine, and move. Once you understand what matter is, topics such as atoms, molecules, density, and chemical reactions become much easier to follow.
This guide starts with the simple definition, then builds up step by step: what matter is made of, the main states of matter, how matter can change state, and how to tell matter apart from energy and empty space. It includes examples, a comparison table, and a FAQ section for quick revision.
Def of Matter: The Simple Definition
The def of matter in school science, the definition most students are asked for, is usually given as: matter is anything that has mass and occupies space, also called volume. Mass is a measure of how much matter an object contains, while volume is the amount of space it takes up. If something has both mass and volume, it counts as matter, even if it is invisible, like air, or extremely small, like a speck of dust.
Two common tests help students remember the def of matter. First, can it be weighed? If yes, it has mass. Second, does it take up room? If yes, it has volume. A book passes both tests, so it is matter. A litre of water passes both tests, so it is matter. Air in a balloon also passes both tests, even though it is hard to see, because the balloon becomes heavier and larger when filled.
Light and sound are often confused with matter, but they are forms of energy, not matter. Light does not have mass in the same way as a physical object, and it does not occupy space as a substance does. Heat is also energy, not matter, although heating matter can change how its particles move. Keeping matter and energy separate is an important step in science, because they behave in different ways.
What Is Matter Made Of?
All ordinary matter, the subject of the def of matter, is made of tiny particles called atoms. Atoms are the basic building blocks of elements such as oxygen, carbon, iron, and gold. Atoms can join together to form molecules, which are groups of two or more atoms bonded together. A water molecule, for example, is made of hydrogen and oxygen atoms joined together, and a sugar molecule contains carbon, hydrogen, and oxygen atoms in a specific arrangement.
Atoms themselves are made of even smaller particles, but for most school science, atoms and molecules are enough to explain how matter behaves. The way particles are arranged and how fast they move determines whether a substance is a solid, a liquid, or a gas, and how it reacts with other substances.
In a solid, particles are packed closely together and vibrate in fixed positions. That is why a solid keeps its shape. In a liquid, particles are still close but can slide past each other, so a liquid flows and takes the shape of its container. In a gas, particles are far apart and move freely, so a gas spreads out to fill its container. These differences in particle behaviour explain many everyday observations, from why ice is hard to why steam rises.
Elements, Compounds, and Mixtures
An element is a pure substance made of only one type of atom. Oxygen, iron, and aluminium are elements. A compound is a pure substance made of two or more elements chemically bonded together, such as water or salt. A mixture is a combination of substances that are not chemically bonded, such as air, which contains nitrogen, oxygen, and other gases, or a salad, which contains different foods mixed together.
The distinction matters because compounds have fixed properties, while mixtures can vary. Pure water always has the same composition, but air can contain different amounts of water vapour depending on the weather. Understanding this distinction helps students classify materials correctly in experiments and exams.
States of Matter Explained
The three most familiar states in the def of matter are solid, liquid, and gas. Solids have a fixed shape and a fixed volume. Liquids have a fixed volume but no fixed shape. Gases have neither a fixed shape nor a fixed volume. These definitions are simple to remember and cover most everyday examples.
There are also other states of matter that appear in more advanced science. Plasma, for example, is a state found in stars and in lightning, where gas particles become electrically charged. Bose-Einstein condensates occur at extremely low temperatures and are studied in advanced physics. For most school work, however, solid, liquid, and gas are the main states to know.
Matter can change from one state to another when it is heated or cooled. Melting is the change from solid to liquid, freezing is the change from liquid to solid, evaporation is the change from liquid to gas, condensation is the change from gas to liquid, and sublimation is the change from solid directly to gas. These changes are physical changes, because the substance itself does not become a different chemical, even though its form changes.
Examples of Each State
Solid examples include wood, metal, ice, rock, and glass. Liquid examples include water, milk, oil, and juice. Gas examples include oxygen, carbon dioxide, steam, and the air around us. Some substances can exist in all three states depending on temperature: water is ice when frozen, liquid water at room temperature, and steam when heated strongly.
It is also useful to notice that some materials do not fit neatly into one category at first glance. Jelly, for example, feels soft and wobbly but holds its shape, so it is often treated as a solid with liquid-like properties. Sand flows like a liquid when poured, but each grain is a solid. Science often deals with such borderline cases by looking closely at particle behaviour rather than appearance alone.
Def of Matter: Properties and Measurement
Scientists describing the def of matter use properties, which are features that can be observed or measured. Physical properties include colour, shape, density, melting point, boiling point, and whether a substance conducts heat or electricity. Chemical properties describe how a substance reacts with other substances, such as whether it burns, rusts, or reacts with acid.
Density is a particularly useful property. It is calculated by dividing mass by volume, and it explains why some objects float while others sink. A large piece of foam may weigh less than a small piece of metal, because foam has a lower density. Density also explains why oil floats on water: oil is less dense than water, so it stays on top.
Mass and weight are often confused, but they are not the same. Mass is the amount of matter in an object and does not change when you move to another planet. Weight is the force of gravity acting on that mass, so it can change: an object weighs less on the Moon than on Earth, even though its mass stays the same. In everyday language people often say “weight” when they mean mass, but in science the distinction is important.
Matter, Energy, and Empty Space
A vacuum, often raised when students ask for the def of matter, is often described as empty space, but even a vacuum is not quite nothing in advanced physics. In everyday science, however, a vacuum is treated as a region with very little matter in it. This helps explain why sound cannot travel through a vacuum: sound needs particles to carry it, and a vacuum has too few particles to do so.
Energy can change the def of matter in practice, by changing matter without being matter itself. Heating a solid makes its particles vibrate faster until it melts. Cooling a gas makes its particles slow down until it condenses. Chemical energy stored in fuel can be released as heat and light when the fuel burns, changing the substances involved. These examples show how matter and energy interact, even though they are different concepts.
Conservation of mass is another key idea linked to the def of matter: in a closed system, matter is not created or destroyed during a physical or chemical change, although it may change form. When wood burns, for example, the ash, smoke, and gases together contain the same total mass as the original wood plus the oxygen used, even though the wood itself seems to disappear. This principle helps scientists balance chemical equations and track materials through reactions.
States of Matter at a Glance
| State | Shape | Volume | Particle Behaviour | Examples |
|---|---|---|---|---|
| Solid | Fixed | Fixed | Packed closely, vibrate in place | Ice, wood, metal |
| Liquid | Takes container shape | Fixed | Close, slide past each other | Water, milk, oil |
| Gas | Fills container | Fills container | Far apart, move freely | Oxygen, steam, air |
| Plasma | Fills container | Fills container | Charged particles, high energy | Lightning, stars |
For more plain-English definitions, see related Dooekpo guides such as the explanation of what multimodal text means, the meaning of bildungsroman, and the guide to what simultaneously means.
Def of Matter: Frequently Asked Questions
Is air matter, under the def of matter?
Yes. Air has mass and takes up space, even though it is invisible. You can feel its pressure in a balloon or a tyre, and it can be compressed into a smaller volume.
Is light matter, under the def of matter?
No. Light is a form of energy. It travels through empty space and does not have mass or volume in the way that a solid, liquid, or gas does.
What is the difference between mass and weight?
Mass is how much matter an object contains and stays the same everywhere. Weight is the force of gravity on that mass and changes with gravity, so it is different on the Moon and on Earth.
Can matter be created or destroyed, under the def of matter?
In ordinary chemical and physical changes, matter is conserved in a closed system: it changes form but the total mass stays the same. Advanced physics deals with special cases, but conservation of mass is the rule for school science.
Why does matter change state, under the def of matter?
Matter changes state when heating or cooling changes how fast its particles move. Heating usually gives particles more energy to move apart, while cooling slows them down so they pack more closely together.
Conclusion
The def of matter is simple to state and powerful to use: matter is anything that has mass and takes up space. From atoms and molecules to solids, liquids, and gases, this one definition helps explain the physical world around us, from a glass of water to the air we breathe. By remembering the difference between matter and energy, between mass and weight, and between physical and chemical changes, students can approach science with greater confidence. Whenever you meet a new substance, ask the two basic questions — does it have mass, and does it take up space? If the answer to both is yes, you are looking at matter.
