7 - Density

Each substance consists of very small particles that together form the mass of the substance.
These small particles are called molecules.
In general you can say:

  In the case of a solid, the molecules are close to each other >> high density.

  With a liquid, the molecules are further apart from each other >> lower density.

  With a gas, the molecules are 'far' from each other >> lowest density.

Note: there are exceptions to this rule because molecules of different substances also have a different structure.


You can calculate density, mass and volume with the formula:

ρ = m / V         (ρ is a greek letter and you pronounce 'rho')

In this is:

ρ   the symbol for   density    the unit is:    g/cm3   or   kg/dm3
m  the symbol for   mass the unit is:    g   or     kg
V   the symbol for   volume the unit is:   cm3   or    dm3

 

Example 1:
Calculate the density if m = 40 g and V = 10 cm3.

F: ρ = m / V
i: ρ = 40 / 10
A: ρ = 4 g/cm3

 

Example 2:
Calculate the mass if ρ = 4 g / cm3 and V = 10 cm3.
F:                   ρ = m / V
i:                    4 = m / 10
A:          4 × 10 = m           
(/ 10 becomes × 10 at the bottom of the fraction. 'Divides' becomes 'times')
                     m = 40 g      

 

Example 3:
Calculate the volume if ρ = 4 g / cm3 and the mass = 40 g
F:                 ρ = m / V
i:                  4 = 40 / V
A:          4 × V = 40             
(/ V becomes × V at the bottom of the fraction. 'Divides' becomes 'times')
                    V = 40 / 4        (Leave greatness. 'Times 4' becomes 'divide by 4')
                    V = 10 cm3