Density Dive
Why does steel sink and a balloon float? Dive into density and the particle model: calculate mass ÷ volume, picture the particles in each state, and track what happens when matter changes state.
Revise this, the fun way
Play it interactively, earn XP and build a streak, free.
Start revising freeWhat you'll cover
Density Dive 🌊
**Density** is how much mass is packed into a given space. It explains why a small lump of lead feels heavy while a big bag of feathers feels light. Behind it lies the **particle model** — how tightly the particles are packed. Dive in.
Density = mass ÷ volume 🧊
**Density = mass ÷ volume** (the symbol is ρ, said 'rho'). Common units are **g/cm³** and **kg/m³**. A block with a mass of 60 g and a volume of 20 cm³ has density 60 ÷ 20 = **3 g/cm³**. The same equation rearranges to mass = density × volume.
Work out the density
An interactive activity.
The particle model 🔬
Everything is made of particles, arranged differently in each state: • **Solid** — packed in a fixed, regular pattern; particles vibrate in place. • **Liquid** — close together but free to move around each other. • **Gas** — far apart, moving quickly in all directions.
Which box is the gas?
An interactive activity.
Match each change of state
- Melting
- Freezing
- Boiling
- Condensing
- Solid → liquid
- Liquid → solid
- Liquid → gas
- Gas → liquid
Spacing sets the density 📉
The particle model **explains** density. In a solid the particles are packed tightly, so a lot of mass fits in a small volume — **high** density. In a gas the particles are spread far apart, so the same volume holds far less mass — **low** density. Same particles, very different packing.
Why so light?
Why does a gas have a much LOWER density than the same substance as a solid?
- Its particles are spread far apart, so less mass sits in the same volume
- Its particles become much heavier
- Its particles grow bigger
- It loses some of its particles
Measuring density 📏
For a **regular** solid, measure the sides to get the volume, and weigh it for the mass. For an **irregular** solid you cannot use a ruler, so you use **displacement**: lower it into water and measure how much the water level rises. That rise IS the volume of the object.
Order the method
An interactive activity.
Changes of state ♻️
Heating or cooling can change the state — melting, freezing, boiling, condensing. These are **physical** changes: only the arrangement of the particles changes, and they can be **reversed**. Crucially, **no particles are created or destroyed**, so the **total mass stays the same**.
Changes of state facts
Pick the TWO statements that are correct about changes of state.
- The total mass stays the same
- They are physical changes and can be reversed
- A brand-new substance is created
- The substance gains mass as it melts
The dive rules
Density is mass divided by _____. In a gas the particles are _____ apart, which gives it a low density. A change of state is a physical change, so the total _____ stays the same.