LESSON
24
hat is density?
Rocks are heavy. A small box of rocks has a large
mass. Yet a box of the
same size containing corks has a small mass.
How can objects that are the same size have diffe
rent masses? Scientists
explain it this way:
All matter is made up of atoms. All atoms have mass
. Some matter has
more massive atoms than others. The more massive
the atoms, the greater
the mass.
Matter has mass. It also takes up space. The amount
of space that matter
takes up is called volume.
The atoms of some kinds of matter are more tight
ly packed than the
atoms of other kinds. More atoms in a volume mea
n more mass in that
volume.
Two properties of matter are important in the pull
of gravity:
• the mass of each atom
• the number of atoms in a given volume
The mass of a given volume of matter is called its dens
ity.
It is the differences in densities that give objects of the
same size different
masses.
For example, gold is about twice as dense as copp
er. This means that if
a piece of copper has a mass of 50 grams, then a piece
of gold the same
size would have a mass of 100 grams.
How do you figure density? It is easy. Use this simp
le formula.
Density =
Mass
Volume
FIGURING VOLUME
r (cc).
n cubic unit is a cubic centimete
mo
com
e
On
its.
un
ic
cub
in
Volume is measured
three numbers:
can be found by multiplying
x
bo
a
e
lik
ped
sha
t
jec
ob
an
The volume of
length x width x height.
time ters
centimeters wide, and 2 cen
3
g,
lon
rs
ete
tim
cen
5
box
a
What is the volume of
Example:
high?
volume= 1xwxh
volume =5cm x3cm x2cm
(55x3x2=30)
rs
volume = 30 cubic centimete
t
length
5cm
M
Figure A
xes
0
centimeter bo
This means that 30 one-cubic
can fit inside this box.
Figure B
FIGURING DENSITY
s a mass of 120 grams. Let us
30 cubic centimeter box ha
Now let us say that this same
density.
I cm
mass
Density =
volume
Density =
120 grams (g)
30 cubic centimeters (cc)
(120 + 30 = 4)
timeter
Density = 4 grams per cubic cen
(4 g,' cc)
Another .v y of saying this is:
substance has a
Each cubic centimeter of this
mass of 4 grams.
Figure C
find its
COMPARING DENSITIES
Equal volumes of different substances have different
masses.
Each one of these cubes has a volume of on
:uhic c wcntimeter.
Each substance has a different mass.
Each substance has a different density.
2.7 grams
7.9 grams
i gram
19.3 grams
.5 grams
.9 grams
Figure D
Answer these questions.
1. Which substance has the greatest density?
2. Which substance has the lowest density?
3. Iron, aluminum, and gold are metals. Which of
the metals has the grea
test density?
4. Which of the metals has the lowest density?
5.
Anything that is Less dense than water will float. Whi
ch two substances will float on water?
UNDERSTANDING DENSITY
a solid aluminum cube,
Figure E shows a solid iron cube and
blanks.
Study the figure. Then fill in the
stuminurn
iron
-2 cm---
2 cm ---
Figure E
cubic centimeters.
iron is
1. The volume of the piece of
2.
The volume of the piece of alumin
cubic centimeters.
um is
the same,
3. The volumes
are, are not
have the same mass.
4.
They
5.
The
6.
Iron is
7.
Aluminum is
8.
Iron is
9.
Aluminum is
do, d
t
has a greater mass.
aluminum, iron
dense than aluminum.
more, less
dense than iron.
more, less
more dense than aluminum.
sometimes, always
less dense than iron.
sometimes, always
are more massive than things
10.
Things made of iron
made of aiuminum.
11.
Things made of aluminum
always, sometimes
than things made of iron.
have a greater mass
can, can never
These are
tricky, Think
before
answering!
UNDERSTANDING VOLUME AND
DENSITY
Figure F
1.
We know that iron is
dense than aluminum.
more, less
2. A volume of iron has
larger, smaller
mass than an equal volume of aluminum.
Vow look at Figure F.
3.
In Figure F the aluminum has a
larger, smaller
4.
This
does, does not
mass than the iron,
mean that aluminum is more dense
than iron.
5. The aluminum is more massive because
there is a
num than there is of iron.
larger, smaller
volume of alumi-
MATCHING
Match each term in Column A with its desc
ription in Column B. Write the correct lette
r in the space
provided.
Column A
-
1.
Column B
mass
ula for density
volume
b) the amount of matter in a substance
density
c) formula for volume
4. length x width x height
d) the mass of a given volume
5. mass
e) the amount of space matter takes up
vnlllrn^
FINDING DENSITIES
sity. The first one has been done
t, find the volume, Th i find the den
firs
w,
belo
ples
exam
the
of
each
For
-you.
aat mass
40 grams
total mass 24 grams
2 cm
length 4 cm
Figure H
Figure G
2.
Finding volume
Volume= Ixwxh
Volume =
Volume=4x2x 1
Volume =
Volume = 8 cubic centimeters (cc)
Finding density
Finding density
Density =
0
Finding volume
Volume= 1xwxh
Density =
mass
mass
volume
volume
24 grams
Density = 8 cubic centimeters
Density =
Density = 3 grams/ cubic centimeter
Density =
g
cc
grams/cc
71
total mass
24 grams
total mass
500 grams
5cm
1 cm, CE
3cm
5 cm
Figure J
Figure 1
3.
4.
Volume=lxwxh
Volume = I x w x h
Volume =
Volume =
Density =
mass
Density = -
volume
g
Density =
Density =
cc
Volume =
cc
Volume =
Density .^.
cc
g/cc
Density =
mass
volume
cc
o/ec
TRUE OR FALSE
In the space provided, write "true" if the sentence is true. Write "false" if the sentence i
All matter has mass and takes up space.
2.
All atoms have the same mass.
3.
An atom of iron is more massive than an atom of aluminum.
4.
A pile of feathers can be more massive than a pile of rocks.
5.
Density has to do only with mass.
6.
Volume tells us how massive matter is.
7.
Ice floats on water.
8.
Ice is more dense than water.
9.
Equal volumes always mean equal masses.
10.
A centimeter is a measure of volume.
REACHING OUT
A measuring cup or graduated cylinder measures liquid volume.
One measurement of volume is the cubic centimeter. Another is the milliliter.
One milliliter (ml) = one cubic centimeter.
1.
What is the total volume of the rock and liquid in this graduated cylinder?
2.
How can you use a graduated cylinder
filled with water to find the volume of an
odd-shaped object like a rock?
Figure K
atse.