States of Matter — Class 3 Science (Samacheer Kalvi)
TN State Board (Samacheer Kalvi) Class 3 Science. Solids, liquids, gases and the changes between them.
1. What matter is
Matter is anything that has mass and occupies space. A stone is matter. So is water, and so is the air in a balloon.
Gases count too. A filled gas cylinder is heavier than an empty one, and the difference is the weight of the gas inside. Anything you can weigh has mass, even when you cannot see it.
2. The three states
| State | Shape | Volume | Examples |
|---|---|---|---|
| Solid | Fixed | Fixed | Stone, ice, wood, pencil |
| Liquid | Takes the container's shape | Fixed | Water, milk, oil, honey |
| Gas | No fixed shape | No fixed volume | Air, steam, cooking gas |
A solid keeps its own shape wherever you put it. Its particles are packed tightly and cannot move past one another.
A liquid keeps the same amount but changes shape to fit the vessel. Pour a glass of water into a bowl and you still have a glassful, spread differently.
A gas fills whatever space it is given. Open a bottle of scent in one corner and the smell reaches the whole room.
3. Liquids are not all alike
It is easy to assume every liquid behaves like water. They do not.
Honey pours slowly and oil more slowly than water. Milk is thicker than water and thinner than honey. What they share is a fixed volume and no fixed shape, and that is what makes them all liquids.
4. Changing state
Heating and cooling move a substance between states.
| Change | Direction | Example |
|---|---|---|
| Melting | Solid to liquid, on heating | Ice becomes water |
| Freezing | Liquid to solid, on cooling | Water becomes ice |
| Evaporation | Liquid to gas | A puddle dries up |
| Condensation | Gas to liquid, on cooling | Drops form on a cold glass |
Water melts at 0 degrees Celsius and boils at 100 degrees Celsius.
Evaporation and boiling are not the same. Boiling happens throughout the liquid at one particular temperature. Evaporation happens slowly from the surface at any temperature, which is why wet clothes dry on a line without ever being heated.
5. The substance stays the same
All of these are physical changes. Ice, water and steam are the same substance in three different states, and freezing steam back would return you to ice.
Nothing new is made, and the change can be reversed.
6. Worked examples
Example 1. Water is poured from a tall glass into a wide bowl. What changes and what does not?
The shape changes to match the bowl. The volume does not change: it is the same amount of water.
Example 2. Why is a filled gas cylinder heavier than an empty one?
Because the gas inside is matter and has mass. Gases weigh less than solids or liquids of the same size, but they are not weightless.
Example 3. Wet clothes dry on a line on a day when the temperature is nowhere near 100 degrees. Which process is this?
Evaporation. It happens from the surface at any temperature, unlike boiling.
Example 4. Drops of water appear on the outside of a cold bottle. Where did they come from?
From water vapour already in the air. The cold surface cooled it, and it condensed into liquid drops.
7. Practice
- Define matter.
- Give three examples each of a solid, a liquid and a gas.
- Which state has a fixed volume but no fixed shape?
- Name the change from solid to liquid, and the change from liquid to solid.
- State one difference between evaporation and boiling.
- At what temperatures does water freeze and boil?
- Why is melting ice called a physical change?
8. Answers
- Anything that has mass and occupies space.
- Solids: stone, wood, ice. Liquids: water, milk, oil. Gases: air, steam, cooking gas.
- A liquid.
- Melting, and freezing.
- Boiling happens throughout the liquid at one temperature; evaporation happens from the surface at any temperature.
- It freezes at 0 degrees Celsius and boils at 100 degrees Celsius.
- Because the substance is still water throughout, and the change can be reversed by cooling.
9. Summary
- Matter is anything with mass that occupies space, and gases are matter too.
- Solids have fixed shape and volume; liquids have fixed volume only; gases have neither.
- Liquids differ widely in how easily they flow, but all share fixed volume and no fixed shape.
- Melting and freezing swap solid and liquid; evaporation and condensation swap liquid and gas.
- Water melts at 0 degrees Celsius and boils at 100 degrees Celsius.
- Boiling is throughout and at one temperature; evaporation is from the surface at any temperature.
- These are physical changes: the substance stays the same and the change reverses.
