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๐ฌ Think about it
Squeeze a balloon and the gas inside packs tighter. Pressure changes density — but mostly for gases. Solids and liquids barely budge. And here's a puzzle: why does ice float on water? Let's find out.
How does pressure affect density in different states?
- For gases, more pressure pushes particles closer.
- So a gas's volume drops and its density rises.
- Liquids are nearly incompressible, so the effect is small.
- Solids change least of all — usually negligible.
Gases
Liquids and solids
Pressure pushes particles closer.
Particles are already close.
Volume drops, density rises a lot.
Density changes very little or negligibly.
๐ก Ever heard of ...
- Ice floats because it is lighter than liquid water.
- Water's density is highest at 4°C.
- On freezing, water particles take up more space (expansion).
- The same mass in more volume means lower density, so ice floats.
๐ฌ Think like a scientist
- Place a raw egg in plain tap water — it sinks to the bottom.
- Think: what change would make the egg float instead?
- Density partly explains why some objects float and others sink.
Important Points
- Pressure mainly increases the density of gases.
- Liquids and solids change density very little under pressure.
- Ice floats because it is less dense than liquid water.
Important Definitions
- Effect of pressure on density — pressure raises the density of gases a lot, but barely affects liquids and solids.
- Expansion (of water on freezing) — water taking up more space as it freezes, making ice less dense than water.
โ Test Yourself
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How does pressure affect the density of a gas?
View Answer
More pressure pushes gas particles closer, so the volume drops and the density increases. -
Why does pressure barely change the density of liquids?
View Answer
Liquids are nearly incompressible, so their volume and density change very little under pressure. -
Why does ice float on water?
View Answer
On freezing, water expands and takes up more space, so ice is less dense than water and floats. -
At what temperature is water's density highest?
View Answer
At 4°C, water has its highest density. -
Why is floating ice important for aquatic animals?
View Answer
Floating ice forms a layer on top that keeps the water below warm enough for fish to survive in cold weather.
๐ NCERT Question 6 — You have a bottle
A 2-litre bottle has 500 mL of water poured in. How much more water can it hold?
View Answer →
