 Buoyancy
is the tendency to rise or
float in water or air.
 Buoyancy causes objects to float in
liquid and gas environments.
 The
buoyancy of a fluid is related to a
fluid’s density.
 Density is the amount of mass in a
certain unit volume of a substance.
 Density
can be described as the
“crowdedness” of the particles that make
up matter.
 Remember when we, our class, acted as
particles in a solid, liquid and a gas?
Think about how packed together we
were. We were densely packed together
just like the particles in the three states of
matter.
 In
scientific terms density refers to the
amount of a substance that occupies a
particular space.
 According to the Particle Theory
different substances have different size
particles.
 Have
a look at pages 132 – 135.
 Pay close attention to when you read
about the relationship with the Particle
Theory and how we are expanding our
understanding of it.
 Take notes on these pages pertaining to
important information.
 The
density of water vapour is less than
the density of liquid water. Why?
 Solid objects can move easily through
liquids and gases.
 According to the particle theory, the fluid
properties of water and of air allow water
particles and air particles to move out of
the way for firmer, non-fluid states of
matter.
 On
page 136 answer questions 1, 2, 3 and
6.
 Be sure to answer your questions
according to the RMS Writing Standards.
 Attractive
forces in the particles of solids
are so strong that the particles cannot be
pushed or pulled apart.
 These same forces are not as strong in a
liquid and gas so they are easily pushed
apart and objects can move between
them.
 You
can push apart particles in a liquid
which explains why you cannot walk
across water.
 The attractive forces of particles in air are
even less dense then water which
explains why you can run faster on land
compared to running though water.
 To
determine a substance’s density you
need to know how much of that substance
occupies a certain space.
 To do this you first need to determine the
mass of the substance.
 Mass
is the amount of matter in a
substance.
 Volume is a measurement of the amount
of space occupied by the substance.
 The volume of a regular shape (cube,
sphere, pyramid...) can be determined
using mathematical formulas.
 How can you measure the volume of an
irregular shape? (hint. Think about using
water.)
 Look
at Figure 5.9B on page 137 in your
text book. This is one method of how to
measure the
Volume of an
Irregular shape.
 The
greatest amount of fluid that a
container can hold is called its capacity.
 Capacity is usually measured in litres or
millilitres.

 Mass
is NOT the same as weight.
 Weight is the force of gravity exerted on
an object.
 Force is a push or a pull, or anything that
causes a change in motion of an object.
 Gravity
is the natural force that causes an
object to move toward the centre of the
Earth.
 All forces, including weight, are
measured in newtons (N).
 On Earth, gravity’s pull is equal to 9.8 N.
So, a bag of sugar with a mass of 2.26 kg
weighs 22.1 N on Earth.
 Using
page 138-139 in the text prepare a
lab report.
 Purpose: To determine the density of a
substance using mass and volume.
 Materials: 500ml beaker, balance, motor
oil, Murphy Oil, chocolate syrup, aloe
vera, water, molasses
 Hypothesis: Predict how the substances
will rate according to density. “I predict
that...”
 Procedure:
complete 1(b) and copy 2, 3,
4, 5, 6 into your notebook. Complete 7 in
your chart.
 Observation: see chart
 Conclusion: Complete questions 2, 3, 9,
10, and 11 from page 140.
 Density
(D) = Mass (m)
Volume (V)
 Density
of solids is usually given in
g/cm³.
 Density of liquids and gases is usually
given in g/L or g/ml.

















Material Density
Air
Aluminum
Blood
Concrete
Copper
Ethanol
Gold
Ice
Iron
Lead
Mercury
Seawater (Saltwater)
Silver
Steel
Water (Freshwater)
White dwarf star
(g/m3)
0.0012
2.7
1.6
2.0
8.9
0.81
19.3
0.92
7.8
11.3
13.6
1.03
10.5
7.8
1.0
1010
 As
long as temperature and pressure stay
the same, the mass-to-volume ratio, or
density, of any pure substance is a
constant, which means it does not
change.
 Read
pages 137 – 143 and complete
questions 1, 2, 3, 4 and 5(in pairs).
 What
is easier? A handstand on land or a
handstand underwater.
 Water
exerts an upward force that helps
support your body.
 Buoyancy
refers to the ability of a fluid to
support an object floating in or on the
fluid.
 The
particles of a fluid exert a force in a
direction opposite to the force of gravity.
 The
force of gravity pulls down while the
force of buoyancy pushes up.
 Buoyant
force is measured in newtons(N).
 Floating
occurs when an object does not
fall in air or sink in a fluid, but remains
suspended in the fluid.
 Why
do you think fluids can support
certain objects? (Hint: Think about when we combined
the oil, water and aloe vera.)
 Density Tower
Lab