Properties of Matter (Viscosity, Density, and Buoyancy) Notes
VISCOSITY
Viscosity: measure of a fluid’s resistance to flow
Fluid: a liquid or a gas
 This property is important in producing goods such as food and motor
oils.
 This is determined by the size and shape of its molecules.
 If molecules are large and have bumpy surfaces, a great deal of friction
is created as the molecules slide past one another which increases the
viscosity. A liquid with large molecules and bumpy surfaces flows at a
slower rate than a liquid made up of small molecules with a smoother surface.
Look at the oil molecule and water molecule.
Which type of molecule would be easier to pour from a
bottle? _____________ WHY? _____________________
Oil Molecule
Water
Molecule
______________________________________________
 As temperature of a LIQUID increases, its viscosity decreases.
Temperature
Viscosity
Temperature
Viscosity
o The additional kinetic energy allows the molecules
to slide past each other with greater ease.
 As the temperature of a GAS increases, its viscosity increases.
o Because gas molecules are far apart, they do not
have to slide over each other very often in order
to flow.
o Raising the temperature actually increases the number of collisions between the molecules,
resulting in an increase in friction and therefore, viscosity.
Examples:
Honey and syrup are both viscous liquids. They are slower
to pour out than water. But the viscosity can change
because of temperature.
If you heat up honey or syrup, it will pour out faster.
If you cool them down, it will pour out slower.
In other words...
Heat ‘em up, Speed ‘em up!!!
DENSITY
Density: the measure of how tightly packed the atoms of a substance are
 Mass per unit volume
Let’s Think:
 A ping pong ball and a golf ball are approximately the same size.
Which one is more dense? ______________________
The density of an object could be increased in two ways:
 if you cram more matter into a particular volume of space (increase mass) or
 if you cram the matter you have into a smaller volume of space (decrease volume—which you could do
with a gas).
Let’s do some math!!!
D = __M__
V
*Remember: To get full credit, you need to show your work!!*
EX:
a) Find the density of a 45 g object that has a volume of 15 mL?
b) If an object has a density of 2 g/mL and a mass of 20 g, what is the volume?
c) Find the mass of object that has a density of 5 g/mL and a volume of 10 mL?
What is the mass in kg?
Density of States of Matter
You already know about the three most common states of matter (solid, liquid, and gas). How does the
density of a substance change when it changes temperature or changes its state of matter?
Q: Which is more dense a liquid or a
solid?
Find the density of water:
A: We learned that the molecules in
solids are closer together. This is why
solids are more dense. Liquids slide
around and are less closely packed.
Liquids are less dense than solids.
Volume =
Mass =
Density =
***Not all solids are denser than liquids.
There is one great and important
exception. What is it?
Water is more dense as a
liquid than a solid. And
good thing, too! Many
forms of life depend on ice
being less dense.
Name one:
List the densities of 3 objects/substances
and record if they float or sink in water
based on their density.
Density: Sink or Float?
Wood block:
Penny:
Olive Oil:
Q: Which is more dense a liquid or a gas?
(Hint: think about how tightly packed the
molecules are.)
What did you find out about floating or
sinking substances and density?
Q: If an object has a density of 1.35 g/mL,
will it float or sink in water?
A:
A:
Density of Substance
Air
Some
Density
0.0013
Common
3
g/cm3
(g/cm )
Substances
Olive
Oil
Wood
(Oak)
Ice
Water
Salt
Water
Bricks
Penny
0.918
g/cm3
0.6 - 0.9
g/cm3
0.92
g/cm3
1.00
1.025
1.84
8.92
g/cm3
g/cm3
g/cm3
g/cm3
Specific Gravity
A concept related to density is the specific gravity (or, even more appropriate, relative density) of a
material, which is the ratio of the material's density to the density of water. An object with a specific
gravity less than 1 will float in water, while a specific gravity greater than 1 means it will sink.
Example - Use the Density to Identify the Material:
An unknown liquid substance has a mass of 18.5 g and occupies a volume of 23.4 mL.
What is the density of the unknown liquid?
D = __M__
V
If we look up densities of some common substances, we can find that ethyl alcohol, or ethanol, has a
density of 790 kg/m3. The liquid may be ethyl alcohol!
BUOYANCY
Buoyancy: the upward force of a fluid (liquid or gas) pushing on an object
 Buoyancy is why you feel lighter in water than on land.
 Buoyancy is why sea animals can grow to be so large. A blue whale is the
largest mammal to have ever lived: up to 100 feet long. The water supports
a whale’s body.
Archimedes Principle:
 Water pushes up on an object immersed in it. The amount of
buoyancy force it exerts on the object equals the amount of
water that is displaced.
 If the water displaced equals or exceeds the weight of the
object it will float.
 The weight of the wood block is equal to the amount of water
displaced, so the block floats.
Example:
An object that weighs 12 lbs is placed in the water. 15 lbs of water is displaced. Does this object sink or
float?
Answer:
This object floats. If the amount of liquid that is displaced is more than or equal to the weight of the object,
the object will float.
Practice: Use the information in problems 1and 2 to decide if the object is floating or sinking.
1. You place an object that weighs 63 lbs into fresh water, but it displaces 62.4 lbs of water. Does this
object float or sink? Why?
2. You place the same object as in problem 1 into salt water. It displaces 63 lbs of water. Does this
object float or sink? Why?
Now for something a little more complicated:
1. A 0.5 Kg toy submarine made of steel is able to float in
a bathtub. When it’s completely submerged, it
displaces 1 Kg of water. What could you do to the toy
sub to make it sink to the bottom?
2. A ping pong ball is dropped down a pipe sticking out of the road. What could you do
to get the ping pong ball back? (HINT: Ping pong balls are 0.01g and displace 0.005g
of water)