Density, Mass & Volume
Why do you think ice floats in water?
Lets explore why!
Archimedes
287 B.C. – 212 B.C.
A little history…
King Hieron II of Syracuse had given the goldsmith a particular amount of
gold to melt down and make into a crown. When the crown was made and
returned to the King, the King was suspicious that the goldsmith had stolen
some of the gold and replaced it with an equal weight of silver.
The king turned to Archimedes for help…
Legend says that Archimedes discovered the
principle of displacement while stepping into a
full bath. He realized that the water that ran over
equaled in volume the submerged part of his
body. The legends goes further and tells that
Archimedes was so excited with his discovery
that he hopped out of the bath, and rushed naked
into the street yelling triumphantly, "Eureka!"
"Eureka!" (Greek word for 'I have found it!).
Mass
Mass is the amount of matter, or stuff, that something
is made of.
***Mass is always measured in grams (g)
Volume
Volume is the amount of space that something
occupies or the amount of space that
something contains.
***Volume is always measured milliliters (mL) or cm3
Volume of Regular
Shapes
Volume = Length x Width x Height
Volume of Irregular
Shapes
Use displacement (the amount of water
that is raised when a solid object is
placed in the water)
How do you calculate water
displacement for irregular objects?
23mL – 20mL = 3mL
Amount you end with – Amount you start with = Volume of the object
Volume of the object is 3 cm
3
Density
Density is the amount of matter (mass) in a given
space (volume)
***Density is always measured in g/cm³
How do you
calculate density?
To find density of an object you
must know the volume and the
mass of that object.
To find the density
1- Find the mass of
the object
2- Find the volume of
the object
3- Divide
Density =
Mass
Volume
Problem 1
The mass of a silver bracelet is 48g, it
occupies a volume of 4cm3, what is its
density?
Problem 2
A 9g sample of a substance occupies a
volume of 3cm³. What is its density?
Problem 3
A rectangular block of Lead (Pb)
measures 2.0 cm X 3.0 cm X 4.0 cm. If
the mass of the Pb block is 48g, find its
density.
Problem 4
A cube of gold (Au), which has all equal
sides, has a side length of 2.0cm. If the
sample is found to have a mass of 88.0 g,
find the density of Au.
Have you wondered why hot air balloons rise?
When the air is heated, it becomes less dense until
the balloon's total density is less than that of the
atmosphere; A hot air balloon is literally floating on
the denser, colder air.
Why is cold air denser than hot air?
Do you know why volcanoes erupt?
The main reason that magma rises to the
surface to erupt at volcanoes is because it is
less dense than the rocks that surround it.
A ship floating on water is a great illustration of the difference
between mass and density. A ship must have a density of less
than 1.0 g/cm3 (the density of water), or it will sink. Ships have
a large mass, because they are made of steel, but because
they have a large volume, their density is less than 1.0 g/cm3. If
enough mass is added to them such that their density goes
above 1.0 g/cm3, they will sink.