Density
Grade 8
Density, Mass and Volume
You have probably heard the terms
mass and volume before in Natural
Sciences and Mathematics. But what
about density? Have you ever used this
word before? Perhaps you have heard
someone describe a cake as very
dense? What does this mean?
This section introduces us to physical quantities that are important when we study science.
Two of these quantities, namely mass and volume, are fundamental properties of matter.
We are going to discuss them first, then we will introduce density. Density is another
property of matter that is very closely related to the first two.
Mass
• The mass of an object or a substance
tells us how much matter it consists of.
The greater the mass of an object, the
more matter it contains.
• Mass is measured in kilograms (kg).
When we measure the mass of small
objects or small amounts of matter we
often measure in grams (g) or even
milligrams (mg).
• 1kg = 1000g
• 1g = 1000mg
Volume
• The amount of space that an object occupies
is called its volume.
• Volume is measured in litres and is calculated
by multiplying the length, width and height of
an object.
• A litre is the space inside a cube that is 10 cm
wide, 10 cm long and 10 cm deep.
When calculating volume, 1 cm x 1 cm x 1 cm = 1 cm3. This is the same as 1
ml. That means that 10 cm x 10 cm x 10 cm = 1000 cm3 which equals 1000 ml
or 1 litre.
What is the volume of milk?
What is the volume of mango juice?
Density
• Density is a measure of how much mass of a
material fits into a given volume.
• We say density is the ratio of mass to volume.
• We can write a mathematical relationship to
show this ratio as follows: density =
mass/volume
m
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