Matter
Chapter Twelve: The Physical
Properties of Matter
• 12.1 Density
• 12.2 Buoyancy
• 12.3 Properties of Materials
12.3 Pressure
• A fluid is a form of matter that flows when
any force is applied, no matter how small.
• Liquids are one kind of fluid, gases are
another.
12.3 Pressure
• A force applied to a fluid creates
pressure.
• Pressure acts in all directions, not just
the direction of the applied force.
12.3 Pressure
• Forces in fluids are more complicated than
forces in solids because fluids can change
shape.
12.3 Pressure
• The units of pressure
are force divided by
area.
• One pascal (unit of
force) is one newton of
force per square meter
of area (N/m2).
12.3 Pressure
• The pressure inside
your tire is what
holds your car up.
Which units are normally seen on car tires?
12.3 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.
12.3 Pressure
• In a car engine high pressure is created by an
exploding gasoline-air mixture.
• This pressure pushes the cylinders of the engine
down, doing work that moves the car.
12.3 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.
12.3 Energy conservation and
Bernoulli’s Principle
• Bernoulli’s principle says the three
variables of height, pressure, and speed
are related by energy conservation.
12.3 Energy conservation 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.
12.3 Energy conservation and
Bernoulli’s Principle
• One of the most important
applications of Bernoulli’s
principle is the airfoil shape of
wings on a plane.
• When a plane is moving, the
pressure on the top surface
of the wings is lower than the
pressure beneath the wings.
• The difference in pressure is
what creates the lift force that
supports the plane in the air.
12.3 Mechanical properties
• When you apply a force to an object, the
object may change its size, shape, or both.
12.3 Mechanical properties
• “Strength” describes the ability of a solid
object to maintain its shape even when
force is applied.
12.3 Mechanical properties
• Elasticity describes a
solid’s ability to be
stretched and then return
to its original size.
• Brittleness is defined as
the tendency of a solid to
crack or break before
stretching very much.
12.3 Mechanical properties
• A ductile material can be
bent a relatively large
amount without breaking.
• Steel’s high ductility
means steel can be
formed into useful shapes
by pounding, rolling, and
bending.
12.3 The arrangement of atoms
and molecules in solids
• If the atoms are in an
orderly, repeating pattern,
the solid is crystalline.
• Examples of crystalline
solids include salts,
minerals, and metals.
12.3 Amorphous solids
• Rubber, wax and glass are
examples of amorphous solids.
• The word amorphous comes
from the Greek for “without
shape.”
• Unlike crystalline solids,
amorphous solids do not have a
repeating pattern of molecules or
atoms.
• Plastics are useful and important
amorphous solids.
Chemistry Connection
Silly Putty
In 1943, James Wright, a
researcher for General Electric,
dropped some boric acid into
silicone oil, creating a gooey
compound.
• He named the compound “Silly Putty” after the
main ingredient, silicone.
• Scientists who study how matter have another
term for Silly Putty: it’s a viscoelastic liquid.
Activity
Make your own viscoelastic liquid
• The exact recipe for
Silly Putty is kept
secret, but you can
make your own
viscoelastic liquid with
ingredients you may
have around the house.