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๐ฌ Think about it
Pour water from a bottle into a glass and it changes shape, but the amount stays the same. You can push your finger through it and it closes back up. Liquids are loose, not free. Let's see what makes a liquid flow.
Do liquids have a fixed shape and volume?
- Liquids take the shape of their container.
- So liquids do not have a fixed shape.
- Their particles are free to move within a limited space.
- But the volume stays the same, so liquids have a definite volume.
Example:
200 mL of water looks different in a bottle, a jug, and a glass, but it is still 200 mL.
In this Activity, we will pour the same water through differently shaped containers to test the shape and volume of a liquid.
Materials needed
Three clean, dry containers of different shapes (A, B, C), water, a marker or paper strip.
Procedure
1. Take three clean, dry containers of different shapes and label them A, B, and C.
2. Mark the 200 mL level in each container using a marker or paper strip.
3. Fill Container A with water up to the marked level.
4. Carefully transfer the water from A to B and observe its shape and level.
5. Now transfer the same water from B to C and observe again.
2. Mark the 200 mL level in each container using a marker or paper strip.
3. Fill Container A with water up to the marked level.
4. Carefully transfer the water from A to B and observe its shape and level.
5. Now transfer the same water from B to C and observe again.
Observation
The water takes the shape of each container, but the level stays at 200 mL in all three.
Explanation
Liquids have no fixed shape because their particles are free to move. The volume stays the same, so liquids have a definite volume. (If a container is not clean, a little water sticks to the walls and the next level may be slightly less than 200 mL.)
โ Summary
- Water poured around
- Shape keeps changing
- Volume stays 200 mL
- Liquids flow freely
How do interparticle attractions in liquids compare with solids?
- You can move a finger through water without cutting it.
- The water closes back as soon as you remove your finger.
- So attractions in liquids are slightly weaker than in solids.
- But they are still strong enough to keep particles close.
Solid
Liquid
Particles fixed; only vibrate.
Particles free to move in a limited space.
Definite shape and volume.
Definite volume but no fixed shape.
Very strong interparticle attractions.
Slightly weaker attractions than solids.
What is the boiling point of a liquid?
- On heating, a liquid reaches a stage where it boils.
- The boiling point is where a liquid turns to vapour at atmospheric pressure.
- Particles move so fast that they escape as gas.
- At boiling, vapour forms throughout the liquid as bubbles.
Example:
Water boils into steam at 100°C, with bubbles rising from inside the pot.
How is evaporation different from boiling?
- Evaporation happens at all temperatures, even below boiling.
- It is slow and happens only at the surface.
- Boiling is fast and happens throughout the liquid.
- Both liquids and gases flow, so they are called fluids.
Example:
Spilled water slowly dries up at room temperature — that is evaporation.
Important Points
- Liquids have a definite volume but no fixed shape.
- Boiling point is where a liquid turns to vapour at atmospheric pressure.
- Evaporation is slow surface vapour-forming; liquids and gases are fluids.
Important Definitions
- Boiling point — the temperature at which a liquid boils and turns into vapour at atmospheric pressure.
- Evaporation — the slow change of a liquid into vapour at its surface, at any temperature.
- Fluids — substances that flow and do not keep a fixed shape, namely liquids and gases.
๐ NCERT Question 5 — When spilled on the
Spilled milk flows and spreads, but the glass tumbler keeps its shape. Justify this.
View Answer →
๐ NCERT Question 10 — Grains of rice and
Rice grains and rice flour take the shape of the jar. Are they solids or liquids? Explain.
View Answer →
