What is DensityWhat is Density

What does it mean to be What does it mean to be dense?dense?

Example: Think about Population Density.

• Two Countries have the same number of people living them.–Which one is more densely populated?

Country “A” vs. Country “B”Country “A” vs. Country “B”

“B”“A”

What does it mean to be What does it mean to be dense?dense?

Example:

• Two Countries are the exact same size.

–Which one is more densely populated?

Country “A” vs. Country “B”Country “A” vs. Country “B”

“B”

“A”

Population Density vs. DensityPopulation Density vs. Density

Population Density is a measure of the amount of people in an amount of land.

Density is a measure of the amount of matter in an amount of space.

Density is a Derived UnitDensity is a Derived UnitWhich means it is:Which means it is:

• The amount of matter in an object, which is called MASS.

• The Amount of Space occupied by an object, which is called VOLUME.

A Calculated measurement (NOT a Pure measurement) that depends on…

So what is density?So what is density?• A material's density is defined

as its mass per unit volume.

• It is, essentially, a measurement of how much mass would be in EACHEACH cm3 or ml of the object.

The object to the below has a

MASS of 8.25 ouncesThe object to the right has a VOLUME

of 11 BlocksThat means the DENSITY of

the object is 0.75 ounces per block Now remove the

RED block from the object.

What’s the MASS of the RED block?

0.75 ounces

What if we took a BLUE one instead? What would be the MASS of the BLUE block?

0.75 ounces

• Every object around us is made of Molecules.

• Different types of molecules can have different masses and different sizes

• There is little or no space between the molecules of objects. (The molecules are always touching)

• By changing the number or type of molecules in an object you can change the density of the object.

• Imagine that a Beach ball represents a molecule. The size of the beach ball can change depending on how much force is applied to it.

• To understand what is happening inside an object: imagine that we fill the entire classroom with beach balls (from wall to wall – floor to ceiling)

• Is it possible to make this “object” more dense by adding another beach ball?

• Is there another way to make this more dense?

• YES. Since the walls give a little, we can force one or two more beach balls into the same space. This is also true of molecules

To calculate Density:To calculate Density:

MASS of the Object

D =Volume of the Object

To calculate Density:To calculate Density:• Example:

– 1) Mass = 4.50 g

– 2) Volume = 80.0 ml

• STEP 1 = Mass

VolumeStep 2 =

80.0 ml4.50 g

=0.056 g/ml

Notice that neither label will cancel

out. So both must be kept.

Density’s LabelDensity’s Label• Mass is always measured in grams• Volume of LiquidsLiquids and GasesGases are

measured in Milliliters

• Volume of Solids are measured in cm3

• This means:

1 ml of Liquid will fit into a cube 1cm x 1cm x 1cm (1 ml = 1 cm3)

Density’s LabelDensity’s Label• Density of Liquids or Gases:

– g/ml

• Density of Solids:

– g/cm3

How to measure Mass?

•Use the Scale– For Liquids and Gases you will need to

subtract the mass of the container

How to measure Volume?• Liquids:

–Use the GRADUATED CYLINDER.

• Solids:–Use Displacement (Direct or Overflow)

–Use volume formulas

Cubes: V = L x W x H

Cylinders: V = x r2 x Hπ

Example 1Example 1• What is the Density of the

following Solid Object?

L = 2.45 cmL = 2.45 cm

W = 2.00 cmW = 2.00 cm

H = 2.75H = 2.75

cmcm

MASSMASS

150.00 g150.00 g

Answer (Example #1)Answer (Example #1)• Mass = 150.00 g• Volume = L x W x H

V =V = (2.45 cm) x(2.45 cm) x (2.75 cm)(2.75 cm)(2.00 cm) x(2.00 cm) x

V = 13.48 cmV = 13.48 cm33

d =d =13.48 cm13.48 cm33

150.00 g150.00 g= = 11.13 11.13 g/cmg/cm33

STEP ONE

STEP TWO

STEP THREE

MV

=

Example 2Example 2• What is the Density of the

following Solid Object?

r = ½ of Dr = ½ of D H = 8.00H = 8.00

cmcm

MASSMASS

175 g175 g

D = 6.00 cmD = 6.00 cm

Answer (Example #2)Answer (Example #2)• Mass = 175 g• Volume = π x r2 x H

V =V = (3.14)x(3.14)x (8.00) (8.00) cmcm

(3.00) x (3.00) x cm cm

V = 226.08 cmV = 226.08 cm33

d =d =226.08 cm226.08 cm33

175 g175 g= = 0.774 0.774 g/cmg/cm33

STEP ONE

STEP TWO

STEP THREE

MV

=

(3.00) x (3.00) x cmcm

Example 3Example 3• What is the Density of the

following Irregular Object?

Volume of Volume of Overflowed Overflowed HH22O = 22.7 mlO = 22.7 ml

MASS of Object = 54.00 gMASS of Object = 54.00 g

Answer (Example #3)Answer (Example #3)Mass = 54.00 g

Volume = Volume of Overflowed H2O

V = 22.7 cmV = 22.7 cm33

d =d =22.7 cm22.7 cm33

54.00 g54.00 g= = 2.38 2.38 g/cmg/cm33

Since the OBJECT is SOLID use this Label

MV

=

One ml = One cm3

Example 4Example 4• What is the Density of the

following Irregular Object?

Volume of Volume of Displaced HDisplaced H22O O

= 5.0 ml= 5.0 ml

MASS of Object = 8.25 gMASS of Object = 8.25 g

Volume Before =

7.5 mlVolume After =

12.5 ml

Answer (Example #4)Answer (Example #4)Mass = 8.25 g

Volume = Volume of Displaced H2O

V = 5.0 cmV = 5.0 cm33

d =d =5.0 cm5.0 cm33

8.25 g8.25 g= = 1.65 1.65 g/cmg/cm33

Since the OBJECT is SOLID use this Label

MV

=

One ml = One cm3