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What is happening? Why?
Why do these float?
Density
What is density?
Density is a ratio of how much
matter there is in a certain amount
of space.
 A measure of how many particles
are packed into a certain area.

More dense = more particles in a space
Less dense = less particles in a space
How do I find density?

I need to find out how much stuff (mass) is in
a certain amount of space (volume)
What instruments do I need?

To find the mass of
an object
 Triple Beam
Balance
 Units are g

To find the volume
of the object


Ruler or graduated
cylinder
Units are cm3 or mL
How do I calculate density?

Density = mass
OR
volume
mass ÷ volume.

Units for density:
or
g
cm3
g
ml
ALWAYS
REMEMBER
UNITS!
Does the sample size affect the
density of an object?


In other words, if I
break off a piece of
this cube, will it have
a different density
than the whole
piece?
NO!!!
Density is based on total mass
divided by total volume.
 When one changes, the other also
changes, so the density (which is
a ratio) stays the same!!!

Which one is more dense?

Which table group is most dense in the
classroom?

How about this: Which square is more dense?
Density of Water



Water has a density of 1g/mL
If an object has a density greater than 1g/mL, it
will sink in water
If an object has a density of less than 1g/mL, it
will float in water.
What do we know about the
density of diet coke vs. coke vs.
water?
Do liquids have different
densities?






Yes! So what happens when you mix
them?
They form layers with the highest density
falling to the bottom.
Alcohol = .80 g/ml
Vegetable Oil = .90 g/ml
Water = 1.0 g/ml
Salt Water = 1.2 g/ml
The density of the liquid
affects how you float too!


Denser liquids help you float more easily.
That is why it is easier to float in the
ocean, than in a freshwater lake.
Illustrating Density
Metals have different densities



Lead 11.3 g/cm3
Aluminum 2.7 g/cm3
These are all over 1.0 g/ml and most ships
are made of metal. So how do boats float?
Explain why one bowling ball
floats and one sinks
http://www.youtube.com/watch?v=NqNGW0oOXE4
Density affects many of Earth’s
processes
Density helps create ocean currents
Density helps move melted rocks
under Earth’s crust
crust
mantle
core

Hot material rises, cooler material sinks,
creating a current, called a Convection
Current
Solid Land has different densities


Continental Plates – lighter, thicker, made of
granite
Oceanic Plates – heavier, thinner, made of
basalt
Convergent Boundary

Plates move toward each other
The more dense oceanic plate subducts under the
less dense continental plate
Normal and Low bone densities

Low density bones break more easily.
Temperature can affect
density


Remember. . . Warm air rises.
So this means warm air is less dense than
cold air and it rises
Density causes your attic to be hot in
the summer