Water can be ice, which is a solid. It can be liquid water. It can be steam, which is a gas. Solid, liquid and gas are the three states of matter found most often on Earth. Plasma is a fourth state of matter. The Sun is a ball of plasma. A solid, like an ice cube, keeps its shape.
In a solid, the tiny particles are packed tightly together. In a liquid, they are close together. They can slide past one another. In a gas, they are far apart. They move around on their own. A gas is easy to squeeze into a smaller space. Liquids and solids hardly change their size when squeezed.
Gases can be turned into liquids by cooling them. Liquids can be turned into solids by cooling them more. Melting is a solid changing into a liquid. Freezing is a liquid changing into a solid. At normal air pressure, water freezes at 0 degrees Celsius. It boils at 100 degrees Celsius. Heat liquid water enough. It turns into a gas called steam.
Evaporation is liquid water changing into water vapor, a gas. Condensation is water vapor turning back into liquid water. Drops of water form on the outside of a glass of ice water. This is because water vapor in the air gets cold. Clouds form when water vapor, an invisible gas, turns into liquid water droplets.
Ice is a solid. Ice floats because it is less dense than liquid water. In most other substances, the solid is denser than the liquid. Water expands when it freezes. So ice takes up more room than the liquid water it came from. Dry ice is frozen carbon dioxide. It turns straight into a gas instead of melting.
Matter is anything that has mass and takes up space. Air is a mixture of gases. It is mostly nitrogen, about 78 percent, and oxygen, about 21 percent. Air, the gas around us, is matter. Gases take up space. That is why a balloon inflates when it is filled. Air has mass, and because of gravity on Earth it also has weight.
Words to know
- particles: tiny bits
- condensation: gas to liquid
- evaporation: liquid to gas
- plasma: fourth state
The short version
Solids, liquids and gases are the three states of matter commonly found on Earth. A solid keeps its shape, a liquid takes the shape of its container, and a gas spreads out to fill the whole container. Heating or cooling can change a substance from one state to another.
Quick facts
- Water can be ice (a solid), liquid water, or steam (a gas).
- At normal air pressure, water freezes at 0 degrees Celsius and boils at 100 degrees Celsius.
- Dry ice is frozen carbon dioxide, and it turns straight into a gas instead of melting.
- Ice floats because it is less dense than liquid water.
- Plasma is a fourth state of matter, and the Sun is made of it.
What are the states of matter?
Solids, liquids and gases are the three states of matter commonly found on Earth. In a solid, the tiny particles are packed tightly together. In a liquid, they are close together. They can slide past one another. In a gas, they are far apart. They move around on their own. Plasma is a fourth state of matter, and the Sun is made of super-hot, electrically charged gas called plasma.
How does matter change state?
Gases can be turned into liquids by cooling them, and liquids into solids by cooling them more. Melting is a solid changing into a liquid, and freezing is a liquid changing into a solid. When liquid water is heated enough, it turns into a gas called steam. Condensation is water vapor, a gas, turning back into liquid water.
Why does ice float on water?
Ice floats because it is less dense than liquid water. Water expands when it freezes, so ice takes up more room than the liquid water it came from. In most other substances, the solid is denser than the liquid.
