DENSITY
GRADE 8
SCIENCE
Density, Volume and Mass
 Density is the relationship between an object’s
volume and its mass.
 Describes the crowdedness of atoms.
 The more squished together atoms are, the more
dense the substance will be.
 Unique for every substance!
Volume & Mass
 Volume is the amount of space the object occupies,
 Mass is the amount of matter in a substance, often
measured with a balance scale (sort of like weight)
 Weight is not the same as mass! Weight is the force
of gravity on an object
Density and Temperature
As a substance is heated, it’s particles spread
out therefore lowering its density.
Place each state in order from LEAST dense to
MOST dense: Solid Gas Liquid
LEAST DENSE
- Have more space between atoms;
- Are LESS dense than liquid
- The attractive forces between atoms is not strong
enough to stop solids from pushing them apart.
- LESS dense than solids, but MORE dense than liquids
MOST DENSE
- Do not have a lot of space between atoms;
- The most dense of all the sates
The equation for density
Density is the mass of a substance divided by its volume:
 Solids = grams/cubic centimeters
 Liquids = grams/milliliters
Formula to determine the volume of a rectangular solid:
Length x Width x Height
Volume and Density
Question:
What is the density of an object with a mass of 10 g
and volume of 2 cm3?
Answer:
Try It!
Complete the Density Worksheet 
DENSITY POP QUIZ
1. Calculate the density of a block of wood
measuring 5cm x 10cm x 12 cm. The mass
of this block is 45g. (/6)
2. Knowing that the density of water is
1 . 0 g / c m 3, w o u l d t h i s b l o c k o f w o o d s i n k o r
float in water? (/1)
(NOTE* POINTS ARE GIVEN FOR THE EQUATIONS USED TO
CALCULATE BOTH VOLUME & DENSITY, PLUS ANSWERS GIVEN
WITH CORRECT UNITS!!)
/7
Buoyancy
 Buoyancy is the
tendency for materials
to sink or float in a
liquid
 The upward force
exerted on objects in a
fluid is called buoyant
force.
Buoyancy Continued…
Floating occurs
when an object does
not fall or sink
 The atoms of the fluid
exert a force in the opposite
direction of gravity
Buoyancy Continued
The shape of an
object can create an
average density that
is less than the fluid it
is submerged in
What is AVERAGE DENSITY?
The total mass of an object
divided by its total volume
EXAMPLE:
A steel boat can float on
water even though steel is
more dense than water.
Buoyancy in Fish?
 The air bladder in fish
contains a mixture of air
and water
 The fish’s depth in the
water depends on how
much air is inside the sac.


The more water in the sac
the lower the fish sinks.
The more air in the sac
the higher the fish rises.
 This is how a submarine
works underwater!
Archimedes
http://ed.ted.com/lessons/mark-salata-how-taking-a-bath-led-to-archimedesprinciple
Archimedes
 Archimedes used water displacement to
determine the volume of the kings crown,
then he weighed it to find the mass.
 The volume of water displaced would be
equal to the volume of the crown.
Calculating the Density of Irregularly Shaped Objects
 If an object floats in water, we can
immediately conclude that it is less dense
than the water.
 If we measure the volume of water displaced
by the object when it is placed into the
container of water, we can calculate the
weight of the object, because its weight will
be equal to the weight of the water it
displaces.
Example
Mass = 25.5 g
25.5 g
Volume = 18 – 5 = 13 mL
Water
level =
5 mL
Water
level =
18 mL
Density = m / V
Density = ?
 YOUR CHALLENGE:
Using Archimedes Principle:
1. Calculate the density of a marble
2. Calculate the density of your pen or
pencil
Neutral Buoyancy
 He also found that if the mass of an object is lighter
than the volume of water it displaces then it will
float.
 When gravity = buoyancy, it is known as neutral
buoyancy.
Force of Gravity = Buoyant Force
1. I CAN write the formula for VOLUME (rectangular object):_________
2. I CAN write the formula for DENSITY:__________
3. I CAN give the units of measurement for density in a LIQUID:_____
4. I CAN give the units of measurement for density in a SOLID:_____
5. I CAN identify this force - the upward force exerted on objects
submerged in a fluid:________________
6. I CAN identify the following definition: this occurs when an object
does not fall in or sink in water, but remains suspended in the
fluid:________________
7. I CAN explain how objects that would otherwise sink (ex. Large
Ships), are able to float (1 sentence please)
8. I CAN rank Solids, Liquids and Gases in order of density from the
LEAST dense to the MOST dense: ________, ________, ________