PROPERTIES OF MATTER 12.2
Chapter Twelve: Properties of
Matter
12.1 Properties of Solids
12.2 Properties of Fluids
12.3 Buoyancy
Chapter 12.2 Learning Goals
Explain how pressure is created in
fluids.
Discuss differences between the
density of solids and fluids.
Apply Bernoulli’s principle to explain
how energy is conserved in fluids.
12.2 Properties of Fluids
 A fluid is defined
as any matter that
flows when force
is applied.
 Liquids like water
or silver are kinds
of fluid.
12.2 Pressure
A force applied to a fluid creates
pressure.
Pressure acts in all directions, not
just the direction of the applied
force.
12.2 Forces in fluids
Forces in fluids are more complicated
than forces in solids because fluids
can change shape.
12.2 Units of pressure
The units of
pressure are force
divided by area.
One psi is one
pound per square
inch.
12.2 Units of pressure
The S.I. unit of
force is the pascal.
One pascal (unit
of force) is one
newton of force
per square meter
of area (N/m2).
12.2 Pressure
If your car tires are
inflated to 35 pounds
per square inch (35
psi), then a force of 35
pounds acts on every
square inch of area
inside the tire.
What might happen if you over-inflate a tire?
12.2 Pressure
On the microscopic
level, pressure comes
from collisions
between atoms.
Every surface can
experience a force
from the constant
impact of trillions of
atoms.
This force is what we
measure as pressure.
12.2 Pressure
In a car engine high pressure is created by
an exploding gasoline-air mixture.
12.2 Energy conservation
and Bernoulli’s Principle
Streamlines are
imaginary lines drawn
to show the flow of
fluid.
Bernoulli’s principle
tells us that the energy
of any sample of fluid
moving along a
streamline is constant.
12.2 Bernoulli’s Principle
Bernoulli’s principle says the three
variables of height, pressure, and
speed are related by energy
conservation.
12.2 Three Variables and
Bernoulli’s Principle
If one variable increases along a streamline,
at least one of the other two must decrease.
For example, if speed goes up, pressure
goes down.
12.2 The air foil
One of the most important
The
difference
in
applications
of Bernoulli’s
principle
is is
thewhat
airfoil
pressure
shape of wings on a plane.
creates the lift force
When
a plane is moving,
that supports
the plane
the pressure on the top
in the of
air.the wings is
surface
lower than the pressure
beneath the wings.
12.2 Hydraulics and Pascal’s
Principle
Hydraulic lifts and other hydraulic devices
use pressure to multiply forces and do
work.
The word hydraulic refers to anything that
is operated by a fluid under pressure.
Hydraulic devices operate on the basis of
Pascal’s principle, named after Blaise Pascal.
12.2 Hydraulics and Pascal’s
Principle
Pascal’s principle states that the
pressure applied to an incompressible
fluid in a closed container is
transmitted equally in all parts of the
fluid.
An incompressible fluid does not
decrease in volume when pressure is
increased.
12.2 Hydraulics and Pascal’s
Principle
A small force exerted over a large
distance is traded for a large force
over a small distance.
12.2 Pressure
Pressure is force divided by area.
12.2 Force
You can calculate the force exerted if
you know the pressure and area.
Solving Problems
On a hydraulic lift,
5 N of force is
applied over an
area of 0.125 m2.
What is the output
force if the area of
the larger cylinder
is 5.0 m2?
Solving Problems
1. Looking for:
 …output force
2. Given
 …input force = 5 N; input area = .125 m2
; output area = 5 m2
3. Relationships:
 Pressure = Force Force = P x A
Area
Solving Problems
4. Solution
 Solve for pressure using input force.
 Pressure =
5N
.125m2
= 40 N/m2
 Use Pascal’s law principle and use
equivalent pressure to solve for output
force.
 Force = 40 N x 5 m2 =
m2
200 N
12.2 Viscosity
Viscosity is the property of fluids that
causes friction.
Viscosity is determined in large part
by the shape and size of the particles
in a liquid.
12.2 Viscosity and
temperature
As the temperature of a
liquid increases, the
viscosity of a liquid
decreases.
Increasing the kinetic
energy of the substance
allows the particles to
slide past one another
more easily.
Investigation 12C
Density of Fluids
Key Question:
What is the maximum load a boat can hold before
sinking?
How is the maximum load affected by the density
of the water in which the boat floats?