# Density

## Mass

Mass is the measurement of the amount of matter (or stuff) in an object. Mass is measured in Kilograms (kg). kg is the Basic SI unti for mass.

There are 3 states of matter:

See the below illustration for more examples:

## Volume

Volume is the measurement of the amount of space an object takes up. It is measured in cubic meters (m^{3}).

### Exercise

Question: The image below shows 1kg of feathers and 1kg of rocks. Answer the two questions based on the image below: 1) Which one has a greater volume? 2) Which one has a greater mass? Answer: 1) Rocks, because it covers more volume than the feathers. 2) The rocks and the feathers have the same mass because they both are 1kg of mass.

## Density

Density is defined as mass per unit volume.

Question: There are two identical boxes. Each box has a number of metal balls inside them. Which box is the most dense (highest density)?

#### How to find the density

- Find the mass of the object (M)
- Find the volume of the object (V)
- Density = Mass (g) / Volume (cm
^{3})
- Summary: D = M / V

### Exercise

Assume the mass of an object is 45 grams and it takes up 9 cm^{3} of space, calculate the density.
Solution: **
Density = D = M / V = 45 g / 9 cm**^{3} = 5 g/cm^{3}

### Exercises

### Ways to Affect Density

The equation D = M/V shows that Density is proportional to the Mass (D ∝ M) and is inversely proporptional to the Volume (D ∝ 1/V). In addition, Mass is proportional to the Volume (M ∝ V). Therefore:
- Increase in mass → Increase in density. Decrease in mass → Decrease in density (D ∝ M)
- Increase in volume → Decrease in density. Decrease in volume → Increase in density (D ∝ 1/V).
- Increase in mass → Increase in volume. Decrease in mass → Decrease in volume (M ∝ V).

*Practice: Here is an exercise about density*

*Check your answers here.*

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Date of last modification: 2024