8.8 and 8.9 Density

• Science
• Middelbare school
• vmbo lwoo, vwo
• Leerjaar 2

Learning objectives 

• Describe the concept of density in your own words

• Name the formula for density

• Explain what each quanitity in the formula and their units mean

• Be able to do density calculations, including being able to reaarange the formula

  

As you can see in this picture the copper atoms are smaller than the Aluminium atoms. Therefor more Copper atoms fit in the cube than Aluminium atoms. Copper atoms are also heavier than Aluminium. The combination of more and heavier atoms makes copper more dense than aluminium. We call this density.

As you can see on the picture both objects, the cube of Copper and the cube of Aluminium have the same shape/volume but a different mass.

Density is the mass per unit of volume — the amount of kilograms (kg) per cubic meter (m3) of a material

It can be measured in several ways. The most accurate way to calculate the density of any solid, liquid or gas is to divide its mass in kilograms by its volume in cubic metres.

Units of density

The SI unit of density is kilogram per cubic meter (kg/m3). It is also frequently represented in unit of grams per cubic centimeter (g/cm3).

Volume of cube

Measuring volume of an irregular object

1 volume of the water without the object : V1.

2. Carefully place the object in the water, using a thread.

3. Measure  volume of water with object:V2.

4. Volume of the object = V2 – V1

 The density of water is approximately 1000 kg/m3 and the density of air is approximately 1.2 kg/m3.

·· If objects are placed in water and they sink, they have a density greater than that of water (1000 kg/m3).

· If objects are placed in water and they float, they have a density lesser than that of water (1000 kg/m3).

· If several liquids that don’t mix (immiscible) are placed in the same container the least dense one will rise to the top and the densest one will sink to the bottom.

· This last point also goes for gases, but that’s often harder to see because gases tend to mix with each other very easily.

Converting units

kg/m3 = 0.001 g/cm3 

For example, if you have a density of 3 kg/m³:

3 kg/m³ = 3/1000 = 0.003 g/cm3