Transcript Density

Density
Mrs. Reese
What is density?
1. Density is the measurement of the
compactness of an object.
2. Density is a physical property that is
determined by the ratio of a substance’s
mass to its volume.
3. Mass is how much matter is inside of an
object.
4. Volume is how much space something
takes up.
Density
All substances (solids, liquids, or gases)
have unique densities.
Density is a GREAT way to indentify
unknown substances!
Which one is more dense?
Demonstration: People in a square
How about this: Which square is more
dense?
Which one is more dense?
Now which one is more dense?
What is density?
Density = mass OR
volume
Units for density: g
mass ÷ volume.
OR
cm3
ALWAYS
REMEMBER
UNITS!
g
ml
.
How can density be affected?
There are some factors such as change in
temperature or state of matter that can
affect the density of matter.
As a GENERAL RULE, solids tend to be
more dense than liquids or gases because
their atoms are more compacted within
equal volume.
EX: Liquid gold has a density of 17.3 g/ml while
solid gold has a density of 19.3 g/cm3.
There is ALWAYS an exception!
There is ALWAYS an exception…
When you freeze water, the density of the
ice is LESS than the density of water
(even though they are both the same
substance). When you freeze ice, it
crystallizes and leaves more gaps which
increases the volume (by about 9%) and
therefore the density goes down.
THUS, ICE CAN FLOAT IN WATER!
Water vs. Ice
How can density be affected?
Example: Hot air balloon
When you heat a gas, it expands
(increasing its volume) and therefore
decreasing its density. Warmer air rises
because its density is less than the
surrounding air.
CAREFUL! What Won’t Affect Density?
Cutting an object into pieces WILL NOT
change its density. You have not changed
the particle compaction in any way!
Example: If the density of a piece of
American red oak wood is .74 g/cm3. If
you cut the piece of would in half, the
density would NOT decrease by two, IT
WOULD STAY THE SAME!
What can float on water?
Density of water is 1.0 g/ml
If the density is greater than 1.0 g/ml, then
the object will sink in water.
If the density is less than 1.0 g/ml, then the
object will float in water.
Liquid Layers
If you pour together liquids that don’t mix
and have different densities, they will form
liquid layers.
The liquid with the highest density will be
on the bottom.
The liquid with the lowest density will be
on the top.
Liquid Layers
 Which layer has the highest
density?
 Which layer has the lowest
density?
 Imagine that the liquids have the
following densities:
10g/cm3
6g/cm3
3g/cm3
5g/cm3
 Which number would go with
which layer?
Liquid Layers – Try with your neighbor
 Which liquid has the
highest density?
 Which liquid has the
lowest density?
On your own…
 Your friends at your lunch table all have different
stuff in their lunch. Liquid A has a density of 1.07
g/ml, Liquid B has a density of 0.98 g/ml, Solid C has
a density of 1.12 g/cm3, and Mush D has a density of
1.03 g/cm3. You decide to make a gross combination
of the four in your water bottle. Which order will they
appear in, from bottom to top?




a) Solid C, Mush D, Liquid A, and Liquid B on top?
b) Solid C, Mush D, Liquid B, and Liquid A on top?
c) Solid C, Liquid A, Mush D, and Liquid B on top?
c) Liquid A, Liquid B, Solid C, and Mush D on top?
5 special steps-that’s all you need!
Let’s 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?
Frank also has an eraser in the shape of a
cube. It has a mass of 3g, and each side
of the eraser is 1.0 cm long. What is its
density?
Work on these problems with your neighbor.
Jack has a rock. The rock has a mass of
6g and the volume of the water level went
up from 50 ml to 53 ml when placed
inside. What is the density of the rock?
Jill has a gel pen. The gel pen has a mass
of 8g and a volume of 2cm3. What is the
density of the gel pen?
Al’Licia has a watch. It has a mass of 4g
and a volume of 2cm3. What is the density
of the watch?
Now, try these on your own. ON
CLEAN SHEET OF PAPER….
 A cube made of very old hard wood, has a mass
of 45g and measures 6cm a side, will it sink or
float?
 Mia has a wallet. It has a mass of 15g and a
volume of 5cm3. What is the density of the
wallet?
 A block has a mass of 20g and measures
2cmX4cmX2cm, will it sink or float?
Try these on your own…
From their density values, decide whether
each of the following substances will sink
or float when placed in sea water, which
has a density of 1.025 g/mL.
Gasoline 0.66 g/mL
Asphalt l.2 g/mL
Mercury 13.6 g/mL
Cork 0.26 g/mL