Density

When looking at density, it is important to first understand the states of matter. The three common states of matter are solidsliquids and gases

Understanding Density

The density of an object is its mass for a given volume. For example, let’s compare two blocks with the same volume.

An illustrative diagram of a seesaw, balanced on a triangular fulcrum. On the left end of the seesaw is a transparent cube with few blue spheres inside, labelled 'Low density'. On the right end, closer to the ground due to its weight, is a similar cube packed with many more blue spheres, labelled 'High density'. The depiction suggests the heavier weight of the high-density cube in comparison to the low-density one.

  • The high-density block has a lot of mass packed into its volume
  • The low-density block has a lower mass packed into the same volume

Calculating Density

To calculate the density of an object, we need:

  • The mass of the object
  • The volume of the object

The mass of the object can be measured using a balance and a measuring cylinder can be used to measure the volume of a liquid.

To measure the volume of a solid, measure, submerge it in a graduated cylinder filled with a known amount of water and see how much the water level rises. This rise in water level indicates the volume of the solid. For solids with regular shapes like cubes or rectangles, simply multiply the length by the width by the height.

The equation to calculate density is:

A formula representing the concept of density. The word 'Density' is equated to a fraction with 'Mass' as the numerator and 'Volume' as the denominator.

An equation depicting the formula for density. The symbol 'ρ' represents density, which is equal to 'M' (mass) divided by 'V' (volume).

  • ρ = Density in grams per centimetre cubed (g/cm³)
  • M = Mass in grams (g)
  • V = Volume in centimetres cubed (cm³)

Example

A rock has a mass of 15 kg and a volume of 1 m³. Calculate the density in g/cm³.

Given:

Mass (m) = 15 kg = 15,000 g (since 1 kg = 1,000 g)

Volume (V) = 1 m³ = 1,000,000 cm³

Since:
(1 m)³ = (100 cm)³

1 m³ = 100 x 100 x 100 cm³

1 m³ = 1,000,000 cm³

Now, plug the values into the density formula:

Density (g/cm³) = Mass (g) ÷ Volume (cm³)

So, density = 15,000 g ÷ 1,000,000 cm³

= 0.015 g/cm³

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