Jugami › Physical Science › Matter
Everything you can touch is made of tiny moving particles.
Your desk, the water in your bottle, and the air you're breathing are all matter. Ice cubes melt, puddles dry up, and a cake rises in the oven. Why does a huge ship float while a small pebble sinks? On this page you'll learn what matter is made of, how it changes from solid to liquid to gas, how to measure density, and why matter never just vanishes.
Matter is anything that has mass and takes up space. A rock, a glass of juice, and the air in a balloon are all matter. Light, sound, and heat are not, because they are forms of energy.
Mass is how much matter something has, measured in grams (g) or kilograms (kg). Volume is how much space it takes up, measured in cubic centimeters (cm³) or milliliters (mL). One milliliter is the same as one cubic centimeter.
All matter is made of tiny particles called atoms, far too small to see even with an ordinary microscope. There are about 118 known kinds of atoms, called elements, such as oxygen, carbon, and gold.
Atoms can join together to make molecules. A water molecule (H₂O) is two hydrogen atoms joined to one oxygen atom.
In the simple particle model, the particles of matter are always moving, and the hotter something is, the faster they move.
Go further: meet all the elements on Marie's interactive periodic table.
| State | Shape and volume | Particles | Example |
|---|---|---|---|
| Solid | Keeps its own shape and volume | Packed tightly, vibrating in place | Ice, a pencil |
| Liquid | Takes the shape of its container; keeps its volume | Close together but sliding past each other | Water, milk |
| Gas | Spreads out to fill its whole container | Far apart, zooming around fast | Air, steam |
There is also a fourth state, plasma: a gas so hot that its atoms break apart into charged pieces. Plasma is found in stars like the Sun, in lightning, and in neon signs, where electricity energizes the gas until it glows.
Adding or removing heat can change matter from one state to another. The substance stays the same; only the way its particles are arranged and moving changes.
Change the temperature of some pure water at sea level and watch how its particles move.
At 20 °C, water is a liquid.
At exactly 0 °C or 100 °C, water can be a mix of two states while it changes.
Density is how much mass is packed into a certain volume. A brick and a sponge the same size have the same volume, but the brick has much more mass, so it is denser.
D = m ÷ V
With mass in grams and volume in cubic centimeters, density is in g/cm³. Water's density is about 1 g/cm³.
Anything denser than water sinks in it; anything less dense floats. A huge steel ship floats because its hull is full of air, so the ship as a whole is less dense than water. Ice floats because it is a little less dense than liquid water.
Worked examples (made-up numbers)
A metal cube: mass 60 g, volume 20 cm³. D = 60 g ÷ 20 cm³ = 3 g/cm³. That's more than 1, so it sinks.
A wooden block: mass 30 g, volume 50 cm³. D = 30 g ÷ 50 cm³ = 0.6 g/cm³. That's less than 1, so it floats.
Working backward: 200 cm³ of water has a mass of about 1 g/cm³ × 200 cm³ = 200 g.
A physical property is something you can observe without turning the substance into something else: color, mass, density, hardness, and melting point.
A chemical property describes how a substance can change into a new substance, such as whether it burns or rusts.
In a physical change, the substance stays the same stuff. Melting ice, tearing paper, and dissolving sugar in water are physical changes.
In a chemical change, new substances form. Clues include a new color, gas bubbles, light or heat, or a new smell. Examples: iron rusting, wood burning, baking soda fizzing in vinegar, and a cake baking.
A pure substance has only one kind of matter all the way through. It can be an element (like pure gold or oxygen) or a compound, two or more elements chemically joined (like water or table salt).
A mixture is two or more substances mixed but not chemically joined, so you can separate them again. Trail mix and salad are mixtures where you can see the parts. Salt water and air are mixtures where you can't, because they are blended evenly. You can get salt back from salt water by letting the water evaporate.
The law of conservation of mass says matter is not created or destroyed in physical or chemical changes. The atoms just rearrange. If nothing escapes or gets in, the total mass before equals the total mass after.
When wood burns, it seems to lose mass, but the "missing" matter has gone into the air as gases and smoke. Burning also uses oxygen from the air, so a fair check has to count the gases going in as well as out. In a sealed container, the total mass would stay the same. The French chemist Antoine Lavoisier showed this with careful measurements in the late 1700s.
Ask an adult before you start. Don't taste anything, wipe up spills right away, and wash your hands when you're done.
You need: a clear glass or jar, honey or corn syrup, water with a drop of food coloring, vegetable oil.
Slowly pour in the honey, then the water, then the oil, tipping the glass and pouring down the side. Drop in a grape and a small cork.
Why: The liquids stack by density: honey sinks to the bottom and oil floats on top. Each small object rests on the layer denser than it.
You need: three ice cubes of the same size, three plates, salt, sugar, a timer.
Sprinkle salt on one cube, sugar on another, and nothing on the third. Check every 5 minutes and record which melts fastest.
Why: Salt dissolves in the thin film of water on the ice, which lowers its freezing point, so the ice melts sooner. That's why roads are salted in winter. Sugar works much less well.
You need: a zip-top bag, an ice cube, a kitchen scale.
Seal the ice in the bag and weigh it. Let it melt completely, then weigh the sealed bag again.
Why: The ice changed state, but no matter got in or out, so the mass stays the same: conservation of mass.
You need: a dry glass, ice water, a paper towel.
Fill the glass with ice water, dry the outside, and wait 10 minutes. Wipe the outside with the towel.
Why: Water vapor in the air cools on the glass and condenses into drops. The water came from the air, not through the glass.
Credits: All illustrations on this page are original, hand-coded SVG by Galileo. The share image was drawn in code.
