NOTES—WHAT IS DENSITY?

Density is the amount of mass per unit of
volume; it describes how much matter is
packed into a space.
NOTES—WHAT IS DENSITY?

Density is a characteristic property of matter

A characteristic property does not depend on size (it
will not change even if the amount of matter changes);
therefore density is not dependent on the shape or
amount of the substance
 1mL of water has a density of 1g/cm3
 1000 mL of water has a density of 1 g/cm3

It is used to identify one type of matter from another.

The density of a pure substance is constant (at same
temperature and pressure); it never changes.
CALCULATING DENSITY

You need to measure an object’s mass and
volume

Density is calculated using the formula:
D= m
v

Density = mass (g) ÷ Volume (mL or cm3)

The basic unit for density is g/mL (liquid) or
g/cm3 (solid or gas)
CALCULATING DENSITY

When solving math problems, always show
all work (even when using a calculator)

STEPS:



Rewrite the formula
Substitute measurements into formula
Solve, circle, and label units
Calculating density practice
MUST SHOW WORK
Mass (g)
Volume (cm3)
200
200 mL
500
10 cm3
700
1000 mL
Density (g/cm3
or g/mL)
SIZE AND DENSITY-- Does the
density of a substance change if the
amount changes?


The density of a pure substance does not
change if the size or amount changes
For example:
Find the density of a wooden block
if mass=8g and
volume= 10cm3
Density= ______
 If the block is cut in half
 Mass=
 Volume=
 Density =
Did the density change?
No, because the ratio of mass to volume is all relative



NOTES—WHAT IS DENSITY?
Most dense
least dense

The more space between the atoms, the less dense the
substance is.

In general,
 solids are more dense than liquids
 liquids are much more dense than
gases, but less dense than solids
 gases are the least dense of all
STATES OF MATTER AND
DENSITY
How can you tell if something will
float or sink in a liquid?

First, compare the density of the object/substance
to the liquid it is in.

If an object/substance is more dense than the
liquid, it will sink

If an object/substance is less dense than the
liquid, it will float

If an object/substance’s density is the same
as the liquid, it won’t sink or float to the top; it
will move toward the center of the liquid
How can you tell if something will
float or sink in a liquid?
The density of water is 1 g/mL.
Do you know why ice floats on water?
The density of ice is .92 g/cm3
For example:
•certain types of wood have a density of .8
g/cm3, so they will float in water.
•Steel has a density of 7.8 g/cm3, so it will sink
in water.
•See it in action:
http://www.teachersdomain.org/asset/phy03_vid_zoil/
•http://www.pbs.org/wgbh/nova/balloon/science/density/fillings
ans.html
Ships and boats are often
made of steel. Why do they
float on water?
http://adventure.howstuffworks.com/
cruise-ship.htm/printable
How is density of matter effected
by heat energy?


As temperature increases, so does the amount of energy
The more energy a substance has:
 The more space between its molecules
 The less dense it is

That’s why…

Solids are usually the most dense phase of matter

The molecules are tightly packed.

Solids maintain (keep) definite shape and volume.

The molecules don’t move around; they vibrate

Solids have little energy
How is density of matter effected
by heat energy?

Liquids are less dense than solids

There is more space between the molecules

Liquids do not have a definite shape, but do have
definite volume.

The molecules move slowly, sliding past one
another; liquids have more energy than solids

An exception to the rule: Ice is less dense than liquid
water. Do you know why?
How is density of matter effected
by heat energy?

Gases are the least dense phase of matter

There is a lot of space between molecules

Gases do not have definite shape or volume; they fill the
container they are in.

The molecules move very quickly; they have high energy.

As the molecules gain heat energy, they move faster and
will expand (spread apart)

As the molecules lose heat energy, they move slower and
will contract (move closer together)