Density

• Units: grams per cubic centimetre (g/cm³)
• Formula: Density = Mass ÷ Volume

Solids, liquids and gases

1. Solids

Example: A block of lead has a density of 11.34g/cm³, while a block of wood has a density of 0.6g/cm³.

• Lead sinks in water because it is much denser.
• Wood floats on water because it is less dense.

2. Liquids

The same rules apply to liquids.

• Example: Water's density is 1g/cm³, and honey's density is about 1.42g/cm³.
• Honey sinks in water because it is denser than water.

3. Gases

Example: The density of carbon dioxide is 0.0018g/cm³, and the density of nitrogen is 0.0012g/cm³.

• Nitrogen floats in carbon dioxide because it is less dense.

4. Floatation

Heavy objects don't always sink and light objects don't always float; density determines this.

• Example: A coin sinks in water, but a 12-tonne ship floats. Water has a density of 1g/cm³.

• Objects with a density less than 1g/cm³ will float.

• Objects with a density greater than 1g/cm³ will sink.

5. Importance of Density

• Density is crucial for understanding why objects float or sink.
• It also helps explain phenomena in different states of matter (solids, liquids, gases).
• In engineering, density is important for designing ships, submarines, and airships.

6. Measuring Density

$$Density = \frac{Mass}{volume}$$

1. Regular solids: Measure mass using a balance and volume by calculating dimensions.
2. Irregular solids: Use the displacement method with a graduated cylinder.
3. Liquids: Measure mass by weighing and volume using a graduated cylinder.

$$Mass = Density x Volume$$ $$Volume = Mass/Density$$