General Physics I
Density
Density is the measurement of how tightly a material is packed together. It is defined as
the mass per unit volume. The density of a substance is the relationship between the mass of
the substance and how much space it takes up (volume). The mass of atoms, their size, and
how they are arranged determine the density of a substance.
Understanding density is important because it applies to many areas of life. What density
means in physics is something that determines which clouds will float high in the sky and which
will sink lower. Density determines the motions of gases in the atmosphere as one material
rises over another. It influences what sinks in a body of water and what floats. So what does
density mean? The meaning of density is a measure of how compact matter is. In simple terms,
how much "stuff" is squeezed into a space. The more "stuff," or matter, is squeezed into a
space, the denser it will be.
Do you know that when your family has consumed 1 cubic meter of water for the whole
month, that amount of water has a mass of 1000 kg (1 metric ton)? But nothing compares to
mercury as the densest liquid. One cubic meter of mercury in standard temperature and
pressure has a mass of 13,534 kg. Mercury is 13.5 times denser than water.
By knowing the density of different materials, you can have an idea on which of them will
float or sink in water. Mercury, iron and stone will sink at the bottom because they are denser
compared to water. Wood, oil and air certainly are less dense than water, that’s why they like
to stay at the top of the water. Materials of the same composition will always have the same
density.
Density (ρ) – the mass per unit volume of a material. The SI unit for density is kg/m3.
ρ = m/v
where ;
ρ – density of the material(kg/m³)
m – mass of the material(kg)
V – volume of the material(m3)
A pure gold ring and a gold necklace will have different shapes and sizes but it will always
have the same density regardless of their shape. All materials of the same type will have the
same value for density.
Examples :
Question 1:
Take two boxes that have the same volume. Fill the first box with x balls and the second box
with 6x balls. If the mass of each ball is the same, which box would weigh more?
Solution:
The box that has more balls has more mass per unit of volume. Here the first box contains x
number of balls and the second box contains a 6x number of balls. Since the number of balls in
the second box is 6 times the first box, the second box would weigh more. This property of
matter is called density.
Question 2:
Calculate the density of water if it has a mass of 1160 Kg and a volume of 1 m3?
Solution:
Given :
Mass = 1160 Kg
Volume = by by1 m3
Density is given by the formula: Density = Mass/Volume
ρ = 1160/1 = 1160 kg/m3
Questions 3:
