DENSITY
BUOYANCY
ARCHIMEDES’ PRINCIPLE
WHAT IS MATTER?
 Matter is anything that has mass
and volume.
 Matter is made of atoms and
molecules.
WHAT IS MASS?
Mass = the amount of matter (atoms) in
an object
We measure mass in grams, using a triple
beam balance!

WHAT IS VOLUME?


Volume is the amount of space an object
takes up.
We can find the volume of an object using:



Length x Width x Height= Centimeters Cubed
(solid objects)
A graduated cylinder for liquids. (liters or
milliliters)
Finding how much water is displaced in a
graduated cylinder for irregular shaped
objects. (Initial volume of water subtracted
from the final volume of water.)
WHAT IS WEIGHT?


Weight is the amount of gravitational
force pulling down on an object.
To find weight, we use the formula:

Mass (g) x Gravity (m/s²) = Weight (Newtons
or N)
HOW IS MASS DIFFERENT
FROM WEIGHT?




Mass is the amount of matter in an object
Weight is a force (push or pull). Earth
exerts a gravitational force on objects and
this gravitational force is called the object’s
weight.
The weight of an object changes,
depending on where it is in the universe, &
the amount of gravity acting on it.
The mass of an object does not change,
no matter where it is in the universe.
WHAT IS DENSITY?




Density is the amount of mass in a given
volume
Density is a ratio or comparison of mass
and volume
Density is how tightly packed the atoms
of an object are
DENSITY = MASS PER UNIT VOLUME
DENSITY FORMULA
Density = m
v
The units of density
are:
g/mL OR
3
g/cm
Density Examples
Bag of leaves
less
dense
less
dense
m 200 g
large volume
cork
Brass cylinder
m 200 g
small volume
rubber
smaller mass
larger mass
same volume
same volume
more
dense
more
dense
Density Examples
Aluminum foil
less
dense
Flat
same mass
larger volume
Crushed
same mass
smaller volume
more
dense
m
d
v
Use this triangle to help solve
density problems
WHAT IS THE DENSITY OF
WATER?

Density of water = 1.0 g/mL

Objects with a density above this will sink!
Objects with a density below will float!

Objects with less density
will float on fluids with
greater density.
Objects with more
density will sink in
fluids with less density.
Buoyancy
Buoyancy: the upward force of a fluid that
pushes an object up
Force: a push or pull
Fluid: a substance that flows, that has an
indefinite shape (takes the shape of its
container). Liquids & gases are fluids.
Buoyancy is why objects completely or
partly submerged in a liquid seem to weigh
less than they do in air.
Buoyancy / Density
Relationship
The denser the fluid is, the
more buoyant force it has.
Think about air and water… Both are fluids,
but water has a much greater buoyant force
than air, because it is more dense.
Archimedes’ Principle
"Any object, wholly or partly immersed in a
fluid, is buoyed up by a force equal to the
volume of the fluid displaced by the object.”
OR
 The volume
of an object in
water is equal
to the volume
of the
displaced
water.
 If the weight of the water displaced is less
than the weight of the object, the object will sink.
 Otherwise the object will float, with the weight
of the water displaced equal to or greater than
the weight of the object.
Archimedes' Principle explains why steel ships
float
Gravity vs. Buoyancy-which one wins?
Think of gravity & buoyancy as 2 opposing forces.
Gravity pulls down, buoyancy pushes up.
If weight (gravity) is greater than the displaced
water (buoyancy), the object will sink.
G
B
, object sinks
If the displaced water (buoyancy) is greater than
the weight (gravity), the object will float.
G B , object floats