Density

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Density
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Density

• We know that matter is anything
• that occupies a space and has
• mass.

Density is the amount of matter there is in a
given space.
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Examples

• Metal vs. Wood
• Metal
• Wood

• Water vs. Oil
• Water
• Oil

The amount of particles there are in the metal
and water that occupies the space provided is a
lot more than the amount of particles present in
the oil and wood in the same amount of
space. Water and metal are more dense.
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What do we use density for?

• The space that matter takes up is also known as
  the volume.
• The amount of particle is also known as the mass.

• Density is one of the basic ways to measure and
  compare the physical properties of different
  matter

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Which one is more dense?

• People in a square (popular place vs. not popular
  place)
• How about this Which square is more dense?

A
B

• Do they occupy the same volume?
• Do the have the same amount of particles?

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Which one is more dense?

• Now which one is more dense?

• Do they occupy the same volume?
• Do the have the same amount of particles?

B
A
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• A is more dense because for the small volume it
  holds, it has more matter.
• Even though they have the same amount of
  particles, if A was the same size as B, A would
  have 4 times as much particles.

B
A
A
A
A
A
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What is density?

• To find density, the amount of mass (a
  measurement if the particles present) is divided
  by the volume of the substance.
• Density mass OR mass volume.
• volume

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• Mass is measure in grams and kilograms.
• Volume is measure in cubic centimeters or cubic
  milliliters.
• Mass
• Grams is represented as a g
• Kilograms is represented as a kg
• Volume
• Cubic centimeters cm, solid
• Cubic milliliters mL, liquid
• 1mL3 1cm3
• So if Density mass , Density g or g

ALWAYS REMEMBER UNITS!
3
3
volume
cm3 mL3
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SI Units International System of UnitsModern
metric system, measurements
ALWAYS REMEMBER UNITS!

• Mass
• Grams g
• Kilograms kg
• Length
• Meter m
• Millimeter mm
• Liquid
• Liters L
• Milliliter mL

• Time
• Seconds s
• Milliseconds ms
• Conversions
• Milli m __
• centi c __
• Kilo k __

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Lets try a density problem together

• Frank has a paper clip. It has a mass of 9g and a
  volume of 3cm3. What is its density?

ALWAYS REMEMBER UNITS!
? 9 g 3cm3
D m/V 9g/3cm3 3g/cm3
3g/cm3
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• Frank also has an eraser. It has a mass of 4g,
  and a volume of 2cm3. What is its density?

ALWAYS REMEMBER UNITS!
D ? m 4 g V 2cm3
D m/v 4g/2cm3 2g/cm3
2g/cm3
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Work on these problems with your neighbor.

• Jack has a rock. The rock has a mass of 6g and a
  volume of 3cm3. What is the density of the rock?
• Jill has a gel pen. The gel pen has a mass of 8g
  with a volume of 4cm3. What is the density of the
  rock?

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Now, try these on your own.

• Alicia has a watch. It has a mass of 4g and a
  volume of 2cm3. What is the density of the watch?
• Mia has a wallet. It has a mass of 15g and a
  volume of 5cm3. What is the density of the wallet?

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• To actually calculate density we need measuring
  instruments.
• To measure the mass, we need to use a balance.
• If we use a scale, we measure the weight of the
  object. The weight is the force due to gravity
  pulling down.
• You weigh less on the moon because gravity is
  less. But the amount of particles you are made of
  doesnt change.

• Only mass is measured by the balance because the
  objects mass counteract with the weights on the
  balance.

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Measuring the volume of an object can be very
tricky as well. Most objects are not regular
shapes that we have formulas for to calculate the
volume.
r
Cylinder
Cube or Cubic rectangle
h
h
w
l
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• Frank measured another eraser. He used a balance
  to measure the mass at 4g. However Frank is
  having trouble finding the volume. Can you help
  him?

h 2 cm
w 1cm
l 5cm
ALWAYS REMEMBER UNITS!
V 5cm x 1cm x 2cm 10 cm3
L 5 cm w 1 cm h 2 cm
10 cm3
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• Frank has a cup for soda. He wants to know how
  much soda the cup could hold so he measures the
  volume of the cup. What is the volume?

d
h 10 cm
ALWAYS REMEMBER UNITS!
Before we attempt this problem here are some
clarification
d 4 cm

• p has a numerical value of 3.14.
• The Formula can be written V 3.14 x r 2 x h

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• Whats the area of a circle?
• A p x r 2
• p x r x r
• The volume is just the area of the base times
  the height.
• V p x r 2 x h
• d is twice the radius so d 2 x r
• r d/2

d 4 cm
h 10 cm
d
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• Frank has a cup for soda. He wants to know how
  much soda the cup could hold so he measures the
  volume of the cup. What is the volume?

d
3.14 x r 2 x h d 2 x r, r d/2 r2 r x r
h 10 cm
ALWAYS REMEMBER UNITS!
d 4 cm
r 4 cm/2 2 cm V 3.14 x (2cm)2x 10 cm
3.14x (2cm) x (2cm) x 10 cm 3.14 x 40 cm3
125.6637 cm3 125.66 cm3
V ? r ? Cm d 4 cm h 10 cm
V 3.14 x r 2 x h r d/2
125.66 cm3
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In real life, most objects only resemble these
shapes. Most objects are odd shaped. It is almost
impossible to accurately calculate the volume of
most objects.
Thats where volume by displacement comes into
play. When you think of displacement, what do you
think of?
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In volume by displacement, the displacement of
water or any other liquid is involved. In a
graduated cylinder, we measure the initial volume
of water. V1 Then we drop our object in.
The object takes a certain amount of space. The
water particles rises to a new final volume. VF
The difference in the water levels from before
and after will give you the volume of the object.

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The equation for volume of displacement Volume of
the object Volume of water after Volume
of water before Vo Vf-Vi
What is the volume of this object? Vo ? Vf
Vi Vo
9 mL 7 mL 9mL 7mL 2mL
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Measuring Accuracy

• There many type of errors
• Instrumental The balance is not calibrated right
• Human Error mathematical, looking at the ticks
  on the instruments, eyes play trick on you.
• When measuring Volume of liquids
• Meniscus Bottom arch water of used for measuring
  volume.

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Liquid Layers

• If you pour together liquids that dont mix and
  have different densities, they will form liquid
  layers.
• When liquids dont mix that means theyre
• _____________
• The liquid with the highest density will be on
  the bottom.
• The liquid with the lowest density will be on the
  top.

insoluble
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Liquid Layers

• Which layer has the highest density?
• Which layer has the lowest density?
• Imagine that the liquids on the left have the
  following densities
• 10g/cm3. 3g/cm3.
• 6g/cm3. 5g/cm3.
• Which density would go with which layer?

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Liquid Layers Try with your neighbor

• Which liquid has the highest density?
• Which liquid has the lowest density?
• Which liquid has the middle density?

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Liquid Layers Try on your own!

• Imagine that the liquids on the right have the
  following densities
• 15g/cm3 10g/cm3
• 3g/cm3 9g/cm3
• 7g/cm3 12g/cm3
• Match the colors to the correct densities.

3g/cm3
7g/cm3
9g/cm3
10g/cm3
12g/cm3
15g/cm3
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Review

• What is the formula for density?
• What two methods can be used to measure volume?
• What is a meniscus?
• What happens if you pour together liquids that
  have different densities?
• Will the liquid on the top have the highest or
  lowest density?
• Will the liquid on the bottom have the highest or
  lowest density?

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Super Scientist Question of the Day

• Jake has a book, a ruler, and a balance.
• How can Jake find the density of the book with
  the tools he has?

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• Practice Volume by displacement and density at
• http//www.sciencejoywagon.com/explrsci/media/dens
  ity.htm
• Website is on the Homework page under Friday 6th.