Density, Mass & Volume / Pressure

Spec reference: Ratio, proportion and rates of change
Key idea: Apply formulae for density, mass, volume and pressure.

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Density

$$\text{Density}=\frac{\text{Mass}}{\text{Volume}}\text{Mass}=\text{Density}\times \text{Volume}\text{Volume}=\frac{\text{Mass}}{\text{Density}}$$

• Units: g/cm³ or kg/m³

Example

A metal block has mass 360 g and volume 45 cm³. Find its density.

$$\text{Density}=\frac{360}{45}=\boxed{{\displaystyle 8{\text{ g/cm}}^3}}$$

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Pressure

$$\text{Pressure}=\frac{\text{Force}}{\text{Area}}\text{Force}=\text{Pressure}\times \text{Area}\text{Area}=\frac{\text{Force}}{\text{Pressure}}$$

• Units: N/m² (Pascals, Pa)

Example

A force of 240 N acts on an area of 0.8 m². Find the pressure.

$$\text{Pressure}=\frac{240}{0.8}=\boxed{{\displaystyle 300\text{ Pa}}}$$

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Test Yourself

Question 1 of 5

Mass 500g, volume 100cm³. Find density.