Mass in each cm³
Two jars are the same size. One holds sand. One holds cotton. The sand jar feels heavier. Why?
Mass is the amount of matter in a thing. Volume is the space it takes. One cm³ is the space of a 1 cm cube. One mL is the same space as 1 cm³.
- A balance shows the mass of a stone: 36 g.
- A measuring cylinder holds water at 40 mL.
- The stone goes in. The level rises to 52 mL. The rise is 12 mL.
- 12 mL is 12 cm³. Density = 36 ÷ 12 = 3 g/cm³.
Sand has more mass in each cm³ than cotton does. That is why its jar feels heavier.
New words
- Density — the mass in each unit of volume.
- Displacement — a solid pushes water aside. The rise in level is its volume.
The rule
Rule: Density is mass divided by volume. Water has a density of about 1 g in each cm³.
The unit is g/cm³. It means grams in each cm³. One g/cm³ equals 1,000 kg/m³. That is kilograms in each cubic metre. A solid with an irregular shape has no easy volume to measure. So find its volume from the rise in water level.
| Sample | Mass | Volume | Density |
|---|---|---|---|
| Wood piece | 24 g | 40 cm³ | 0.6 g/cm³ |
| Water | 50 g | 50 cm³ | 1 g/cm³ |
| Stone | 36 g | 12 cm³ | 3 g/cm³ |
| Metal block | 156 g | 20 cm³ | 7.8 g/cm³ |
Watch out!
Cut a block in half. Its mass halves and its volume halves. The density stays the same.
Slide the volume. Match the density.
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