Page 84 - Physics

Physics for Secondary Schools

and its volume leads to an important The relationship between the density, mass,
physical quantity called density. This and volume of a substance can easily be
quantity is the measure of how the remembered by the density-mass-volume
constituent particles of a substance are triangle, shown in Figure 4.3.
parked in a unit volume. If particles are
closely packed in a small volume of a
substance, the substance is said to have
high density and vice versa. Figure 4.2 m
shows high and low density substances.
÷

ρ ( ) x V

(a) High density (b) Low density
substance substance
(more packed) (less packed) Figure 4.3: The density-mass-volume
triangle
Figure 4.2: Concept of density

Thus, density is the extent to which the From the triangle, the horizontal line that
particles of a substance are closely packed separates mass (m) and the other variables
in a particular substance. The more represents division sign. So, whenever it
compact the particles are in a particular is required to fi nd density ρ ( ) or volume
substance, the higher the density of that (V), mass (m) is divide by either volume
substance. (V) or density ρ ( ) , respectively.

Density is the mass of a substance m m
divided by its volume. The symbol used That is, ρ = V and V = ρ .
ρ
for density is the Greek letter, (rho).
Mathematically, density is expressed On the other hand, the vertical line
as: that separates ρ and V represents the

mass (m) of substance multiplication. Therefore, whenever it is
Density, ρ =
volume (V ) of the same substance required to fi nd m, ρ and V are multiplied.

m Thus, m = ρ ×V. Density is an intrinsic
ρ = . property of matter since it is independent
V
of the number of particles contained in
The SI unit of density is kg/m . Another the materials. The densities of common
3
unit used for expressing density is g/cm .
3
substances are given in Table 4.1.
78
Student’s Book Form One

Physics Form 1 Final.indd 78 16/10/2024 20:56